Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1969 insertions, 0 deletions

diff --git a/third_party/rust/encoding_rs/src/handles.rs b/third_party/rust/encoding_rs/src/handles.rs
new file mode 100644
index 0000000000..b5404c01d9
--- /dev/null
+++ b/third_party/rust/encoding_rs/src/handles.rs
@@ -0,0 +1,1969 @@
+// Copyright Mozilla Foundation. See the COPYRIGHT
+// file at the top-level directory of this distribution.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! This module provides structs that use lifetimes to couple bounds checking
+//! and space availability checking and detaching those from actual slice
+//! reading/writing.
+//!
+//! At present, the internals of the implementation are safe code, so the
+//! bound checks currently also happen on read/write. Once this code works,
+//! the plan is to replace the internals with unsafe code that omits the
+//! bound check at the read/write time.
+
+#[cfg(all(
+    feature = "simd-accel",
+    any(
+        target_feature = "sse2",
+        all(target_endian = "little", target_arch = "aarch64"),
+        all(target_endian = "little", target_feature = "neon")
+    )
+))]
+use crate::simd_funcs::*;
+
+#[cfg(all(
+    feature = "simd-accel",
+    any(
+        target_feature = "sse2",
+        all(target_endian = "little", target_arch = "aarch64"),
+        all(target_endian = "little", target_feature = "neon")
+    )
+))]
+use packed_simd::u16x8;
+
+use super::DecoderResult;
+use super::EncoderResult;
+use crate::ascii::*;
+use crate::utf_8::convert_utf8_to_utf16_up_to_invalid;
+use crate::utf_8::utf8_valid_up_to;
+
+pub enum Space<T> {
+    Available(T),
+    Full(usize),
+}
+
+pub enum CopyAsciiResult<T, U> {
+    Stop(T),
+    GoOn(U),
+}
+
+pub enum NonAscii {
+    BmpExclAscii(u16),
+    Astral(char),
+}
+
+pub enum Unicode {
+    Ascii(u8),
+    NonAscii(NonAscii),
+}
+
+// Start UTF-16LE/BE fast path
+
+pub trait Endian {
+    const OPPOSITE_ENDIAN: bool;
+}
+
+pub struct BigEndian;
+
+impl Endian for BigEndian {
+    #[cfg(target_endian = "little")]
+    const OPPOSITE_ENDIAN: bool = true;
+
+    #[cfg(target_endian = "big")]
+    const OPPOSITE_ENDIAN: bool = false;
+}
+
+pub struct LittleEndian;
+
+impl Endian for LittleEndian {
+    #[cfg(target_endian = "little")]
+    const OPPOSITE_ENDIAN: bool = false;
+
+    #[cfg(target_endian = "big")]
+    const OPPOSITE_ENDIAN: bool = true;
+}
+
+#[derive(Debug, Copy, Clone)]
+struct UnalignedU16Slice {
+    ptr: *const u8,
+    len: usize,
+}
+
+impl UnalignedU16Slice {
+    #[inline(always)]
+    pub unsafe fn new(ptr: *const u8, len: usize) -> UnalignedU16Slice {
+        UnalignedU16Slice { ptr, len }
+    }
+
+    #[inline(always)]
+    pub fn trim_last(&mut self) {
+        assert!(self.len > 0);
+        self.len -= 1;
+    }
+
+    #[inline(always)]
+    pub fn at(&self, i: usize) -> u16 {
+        use core::mem::MaybeUninit;
+
+        assert!(i < self.len);
+        unsafe {
+            let mut u: MaybeUninit<u16> = MaybeUninit::uninit();
+            ::core::ptr::copy_nonoverlapping(self.ptr.add(i * 2), u.as_mut_ptr() as *mut u8, 2);
+            u.assume_init()
+        }
+    }
+
+    #[cfg(feature = "simd-accel")]
+    #[inline(always)]
+    pub fn simd_at(&self, i: usize) -> u16x8 {
+        assert!(i + SIMD_STRIDE_SIZE / 2 <= self.len);
+        let byte_index = i * 2;
+        unsafe { to_u16_lanes(load16_unaligned(self.ptr.add(byte_index))) }
+    }
+
+    #[inline(always)]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    #[inline(always)]
+    pub fn tail(&self, from: usize) -> UnalignedU16Slice {
+        // XXX the return value should be restricted not to
+        // outlive self.
+        assert!(from <= self.len);
+        unsafe { UnalignedU16Slice::new(self.ptr.add(from * 2), self.len - from) }
+    }
+
+    #[cfg(feature = "simd-accel")]
+    #[inline(always)]
+    pub fn copy_bmp_to<E: Endian>(&self, other: &mut [u16]) -> Option<(u16, usize)> {
+        assert!(self.len <= other.len());
+        let mut offset = 0;
+        if SIMD_STRIDE_SIZE / 2 <= self.len {
+            let len_minus_stride = self.len - SIMD_STRIDE_SIZE / 2;
+            loop {
+                let mut simd = self.simd_at(offset);
+                if E::OPPOSITE_ENDIAN {
+                    simd = simd_byte_swap(simd);
+                }
+                unsafe {
+                    store8_unaligned(other.as_mut_ptr().add(offset), simd);
+                }
+                if contains_surrogates(simd) {
+                    break;
+                }
+                offset += SIMD_STRIDE_SIZE / 2;
+                if offset > len_minus_stride {
+                    break;
+                }
+            }
+        }
+        while offset < self.len {
+            let unit = swap_if_opposite_endian::<E>(self.at(offset));
+            other[offset] = unit;
+            if super::in_range16(unit, 0xD800, 0xE000) {
+                return Some((unit, offset));
+            }
+            offset += 1;
+        }
+        None
+    }
+
+    #[cfg(not(feature = "simd-accel"))]
+    #[inline(always)]
+    fn copy_bmp_to<E: Endian>(&self, other: &mut [u16]) -> Option<(u16, usize)> {
+        assert!(self.len <= other.len());
+        for (i, target) in other.iter_mut().enumerate().take(self.len) {
+            let unit = swap_if_opposite_endian::<E>(self.at(i));
+            *target = unit;
+            if super::in_range16(unit, 0xD800, 0xE000) {
+                return Some((unit, i));
+            }
+        }
+        None
+    }
+}
+
+#[inline(always)]
+fn copy_unaligned_basic_latin_to_ascii_alu<E: Endian>(
+    src: UnalignedU16Slice,
+    dst: &mut [u8],
+    offset: usize,
+) -> CopyAsciiResult<usize, (u16, usize)> {
+    let len = ::core::cmp::min(src.len(), dst.len());
+    let mut i = 0usize;
+    loop {
+        if i == len {
+            return CopyAsciiResult::Stop(i + offset);
+        }
+        let unit = swap_if_opposite_endian::<E>(src.at(i));
+        if unit > 0x7F {
+            return CopyAsciiResult::GoOn((unit, i + offset));
+        }
+        dst[i] = unit as u8;
+        i += 1;
+    }
+}
+
+#[inline(always)]
+fn swap_if_opposite_endian<E: Endian>(unit: u16) -> u16 {
+    if E::OPPOSITE_ENDIAN {
+        unit.swap_bytes()
+    } else {
+        unit
+    }
+}
+
+#[cfg(not(feature = "simd-accel"))]
+#[inline(always)]
+fn copy_unaligned_basic_latin_to_ascii<E: Endian>(
+    src: UnalignedU16Slice,
+    dst: &mut [u8],
+) -> CopyAsciiResult<usize, (u16, usize)> {
+    copy_unaligned_basic_latin_to_ascii_alu::<E>(src, dst, 0)
+}
+
+#[cfg(feature = "simd-accel")]
+#[inline(always)]
+fn copy_unaligned_basic_latin_to_ascii<E: Endian>(
+    src: UnalignedU16Slice,
+    dst: &mut [u8],
+) -> CopyAsciiResult<usize, (u16, usize)> {
+    let len = ::core::cmp::min(src.len(), dst.len());
+    let mut offset = 0;
+    if SIMD_STRIDE_SIZE <= len {
+        let len_minus_stride = len - SIMD_STRIDE_SIZE;
+        loop {
+            let mut first = src.simd_at(offset);
+            let mut second = src.simd_at(offset + (SIMD_STRIDE_SIZE / 2));
+            if E::OPPOSITE_ENDIAN {
+                first = simd_byte_swap(first);
+                second = simd_byte_swap(second);
+            }
+            if !simd_is_basic_latin(first | second) {
+                break;
+            }
+            let packed = simd_pack(first, second);
+            unsafe {
+                store16_unaligned(dst.as_mut_ptr().add(offset), packed);
+            }
+            offset += SIMD_STRIDE_SIZE;
+            if offset > len_minus_stride {
+                break;
+            }
+        }
+    }
+    copy_unaligned_basic_latin_to_ascii_alu::<E>(src.tail(offset), &mut dst[offset..], offset)
+}
+
+#[inline(always)]
+fn convert_unaligned_utf16_to_utf8<E: Endian>(
+    src: UnalignedU16Slice,
+    dst: &mut [u8],
+) -> (usize, usize, bool) {
+    if dst.len() < 4 {
+        return (0, 0, false);
+    }
+    let mut src_pos = 0usize;
+    let mut dst_pos = 0usize;
+    let src_len = src.len();
+    let dst_len_minus_three = dst.len() - 3;
+    'outer: loop {
+        let mut non_ascii = match copy_unaligned_basic_latin_to_ascii::<E>(
+            src.tail(src_pos),
+            &mut dst[dst_pos..],
+        ) {
+            CopyAsciiResult::GoOn((unit, read_written)) => {
+                src_pos += read_written;
+                dst_pos += read_written;
+                unit
+            }
+            CopyAsciiResult::Stop(read_written) => {
+                return (src_pos + read_written, dst_pos + read_written, false);
+            }
+        };
+        if dst_pos >= dst_len_minus_three {
+            break 'outer;
+        }
+        // We have enough destination space to commit to
+        // having read `non_ascii`.
+        src_pos += 1;
+        'inner: loop {
+            let non_ascii_minus_surrogate_start = non_ascii.wrapping_sub(0xD800);
+            if non_ascii_minus_surrogate_start > (0xDFFF - 0xD800) {
+                if non_ascii < 0x800 {
+                    dst[dst_pos] = ((non_ascii >> 6) | 0xC0) as u8;
+                    dst_pos += 1;
+                    dst[dst_pos] = ((non_ascii & 0x3F) | 0x80) as u8;
+                    dst_pos += 1;
+                } else {
+                    dst[dst_pos] = ((non_ascii >> 12) | 0xE0) as u8;
+                    dst_pos += 1;
+                    dst[dst_pos] = (((non_ascii & 0xFC0) >> 6) | 0x80) as u8;
+                    dst_pos += 1;
+                    dst[dst_pos] = ((non_ascii & 0x3F) | 0x80) as u8;
+                    dst_pos += 1;
+                }
+            } else if non_ascii_minus_surrogate_start <= (0xDBFF - 0xD800) {
+                // high surrogate
+                if src_pos < src_len {
+                    let second = swap_if_opposite_endian::<E>(src.at(src_pos));
+                    let second_minus_low_surrogate_start = second.wrapping_sub(0xDC00);
+                    if second_minus_low_surrogate_start <= (0xDFFF - 0xDC00) {
+                        // The next code unit is a low surrogate. Advance position.
+                        src_pos += 1;
+                        let point = (u32::from(non_ascii) << 10) + u32::from(second)
+                            - (((0xD800u32 << 10) - 0x10000u32) + 0xDC00u32);
+
+                        dst[dst_pos] = ((point >> 18) | 0xF0u32) as u8;
+                        dst_pos += 1;
+                        dst[dst_pos] = (((point & 0x3F000u32) >> 12) | 0x80u32) as u8;
+                        dst_pos += 1;
+                        dst[dst_pos] = (((point & 0xFC0u32) >> 6) | 0x80u32) as u8;
+                        dst_pos += 1;
+                        dst[dst_pos] = ((point & 0x3Fu32) | 0x80u32) as u8;
+                        dst_pos += 1;
+                    } else {
+                        // The next code unit is not a low surrogate. Don't advance
+                        // position and treat the high surrogate as unpaired.
+                        return (src_pos, dst_pos, true);
+                    }
+                } else {
+                    // Unpaired surrogate at the end of buffer
+                    return (src_pos, dst_pos, true);
+                }
+            } else {
+                // Unpaired low surrogate
+                return (src_pos, dst_pos, true);
+            }
+            if dst_pos >= dst_len_minus_three || src_pos == src_len {
+                break 'outer;
+            }
+            let unit = swap_if_opposite_endian::<E>(src.at(src_pos));
+            src_pos += 1;
+            if unit > 0x7F {
+                non_ascii = unit;
+                continue 'inner;
+            }
+            dst[dst_pos] = unit as u8;
+            dst_pos += 1;
+            continue 'outer;
+        }
+    }
+    (src_pos, dst_pos, false)
+}
+
+// Byte source
+
+pub struct ByteSource<'a> {
+    slice: &'a [u8],
+    pos: usize,
+}
+
+impl<'a> ByteSource<'a> {
+    #[inline(always)]
+    pub fn new(src: &[u8]) -> ByteSource {
+        ByteSource { slice: src, pos: 0 }
+    }
+    #[inline(always)]
+    pub fn check_available<'b>(&'b mut self) -> Space<ByteReadHandle<'b, 'a>> {
+        if self.pos < self.slice.len() {
+            Space::Available(ByteReadHandle::new(self))
+        } else {
+            Space::Full(self.consumed())
+        }
+    }
+    #[inline(always)]
+    fn read(&mut self) -> u8 {
+        let ret = self.slice[self.pos];
+        self.pos += 1;
+        ret
+    }
+    #[inline(always)]
+    fn unread(&mut self) -> usize {
+        self.pos -= 1;
+        self.pos
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.pos
+    }
+}
+
+pub struct ByteReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut ByteSource<'b>,
+}
+
+impl<'a, 'b> ByteReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut ByteSource<'b>) -> ByteReadHandle<'a, 'b> {
+        ByteReadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn read(self) -> (u8, ByteUnreadHandle<'a, 'b>) {
+        let byte = self.source.read();
+        let handle = ByteUnreadHandle::new(self.source);
+        (byte, handle)
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+}
+
+pub struct ByteUnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut ByteSource<'b>,
+}
+
+impl<'a, 'b> ByteUnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut ByteSource<'b>) -> ByteUnreadHandle<'a, 'b> {
+        ByteUnreadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn unread(self) -> usize {
+        self.source.unread()
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut ByteSource<'b> {
+        self.source
+    }
+}
+
+// UTF-16 destination
+
+pub struct Utf16BmpHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut Utf16Destination<'b>,
+}
+
+impl<'a, 'b> Utf16BmpHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut Utf16Destination<'b>) -> Utf16BmpHandle<'a, 'b> {
+        Utf16BmpHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_ascii(self, ascii: u8) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_ascii(ascii);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp_excl_ascii(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_bmp_excl_ascii(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_mid_bmp(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_mid_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_upper_bmp(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_upper_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf16Destination<'b> {
+        self.dest
+    }
+}
+
+pub struct Utf16AstralHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut Utf16Destination<'b>,
+}
+
+impl<'a, 'b> Utf16AstralHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut Utf16Destination<'b>) -> Utf16AstralHandle<'a, 'b> {
+        Utf16AstralHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_ascii(self, ascii: u8) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_ascii(ascii);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp_excl_ascii(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_bmp_excl_ascii(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_upper_bmp(self, bmp: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_upper_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_astral(self, astral: u32) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_astral(astral);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_surrogate_pair(self, high: u16, low: u16) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_surrogate_pair(high, low);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_big5_combination(
+        self,
+        combined: u16,
+        combining: u16,
+    ) -> &'a mut Utf16Destination<'b> {
+        self.dest.write_big5_combination(combined, combining);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf16Destination<'b> {
+        self.dest
+    }
+}
+
+pub struct Utf16Destination<'a> {
+    slice: &'a mut [u16],
+    pos: usize,
+}
+
+impl<'a> Utf16Destination<'a> {
+    #[inline(always)]
+    pub fn new(dst: &mut [u16]) -> Utf16Destination {
+        Utf16Destination { slice: dst, pos: 0 }
+    }
+    #[inline(always)]
+    pub fn check_space_bmp<'b>(&'b mut self) -> Space<Utf16BmpHandle<'b, 'a>> {
+        if self.pos < self.slice.len() {
+            Space::Available(Utf16BmpHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn check_space_astral<'b>(&'b mut self) -> Space<Utf16AstralHandle<'b, 'a>> {
+        if self.pos + 1 < self.slice.len() {
+            Space::Available(Utf16AstralHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.pos
+    }
+    #[inline(always)]
+    fn write_code_unit(&mut self, u: u16) {
+        unsafe {
+            // OK, because we checked before handing out a handle.
+            *(self.slice.get_unchecked_mut(self.pos)) = u;
+        }
+        self.pos += 1;
+    }
+    #[inline(always)]
+    fn write_ascii(&mut self, ascii: u8) {
+        debug_assert!(ascii < 0x80);
+        self.write_code_unit(u16::from(ascii));
+    }
+    #[inline(always)]
+    fn write_bmp(&mut self, bmp: u16) {
+        self.write_code_unit(bmp);
+    }
+    #[inline(always)]
+    fn write_bmp_excl_ascii(&mut self, bmp: u16) {
+        debug_assert!(bmp >= 0x80);
+        self.write_code_unit(bmp);
+    }
+    #[inline(always)]
+    fn write_mid_bmp(&mut self, bmp: u16) {
+        debug_assert!(bmp >= 0x80); // XXX
+        self.write_code_unit(bmp);
+    }
+    #[inline(always)]
+    fn write_upper_bmp(&mut self, bmp: u16) {
+        debug_assert!(bmp >= 0x80);
+        self.write_code_unit(bmp);
+    }
+    #[inline(always)]
+    fn write_astral(&mut self, astral: u32) {
+        debug_assert!(astral > 0xFFFF);
+        debug_assert!(astral <= 0x10_FFFF);
+        self.write_code_unit((0xD7C0 + (astral >> 10)) as u16);
+        self.write_code_unit((0xDC00 + (astral & 0x3FF)) as u16);
+    }
+    #[inline(always)]
+    pub fn write_surrogate_pair(&mut self, high: u16, low: u16) {
+        self.write_code_unit(high);
+        self.write_code_unit(low);
+    }
+    #[inline(always)]
+    fn write_big5_combination(&mut self, combined: u16, combining: u16) {
+        self.write_bmp_excl_ascii(combined);
+        self.write_bmp_excl_ascii(combining);
+    }
+    #[inline(always)]
+    pub fn copy_ascii_from_check_space_bmp<'b>(
+        &'b mut self,
+        source: &mut ByteSource,
+    ) -> CopyAsciiResult<(DecoderResult, usize, usize), (u8, Utf16BmpHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let src_remaining = &source.slice[source.pos..];
+            let dst_remaining = &mut self.slice[self.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (DecoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (DecoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_basic_latin(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    source.pos += length;
+                    self.pos += length;
+                    return CopyAsciiResult::Stop((pending, source.pos, self.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    source.pos += consumed;
+                    self.pos += consumed;
+                    source.pos += 1; // +1 for non_ascii
+                    non_ascii
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, Utf16BmpHandle::new(self)))
+    }
+    #[inline(always)]
+    pub fn copy_ascii_from_check_space_astral<'b>(
+        &'b mut self,
+        source: &mut ByteSource,
+    ) -> CopyAsciiResult<(DecoderResult, usize, usize), (u8, Utf16AstralHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = self.slice.len();
+            let src_remaining = &source.slice[source.pos..];
+            let dst_remaining = &mut self.slice[self.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (DecoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (DecoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_basic_latin(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    source.pos += length;
+                    self.pos += length;
+                    return CopyAsciiResult::Stop((pending, source.pos, self.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    source.pos += consumed;
+                    self.pos += consumed;
+                    if self.pos + 1 < dst_len {
+                        source.pos += 1; // +1 for non_ascii
+                        non_ascii
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            DecoderResult::OutputFull,
+                            source.pos,
+                            self.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, Utf16AstralHandle::new(self)))
+    }
+    #[inline(always)]
+    pub fn copy_utf8_up_to_invalid_from(&mut self, source: &mut ByteSource) {
+        let src_remaining = &source.slice[source.pos..];
+        let dst_remaining = &mut self.slice[self.pos..];
+        let (read, written) = convert_utf8_to_utf16_up_to_invalid(src_remaining, dst_remaining);
+        source.pos += read;
+        self.pos += written;
+    }
+    #[inline(always)]
+    pub fn copy_utf16_from<E: Endian>(
+        &mut self,
+        source: &mut ByteSource,
+    ) -> Option<(usize, usize)> {
+        let src_remaining = &source.slice[source.pos..];
+        let dst_remaining = &mut self.slice[self.pos..];
+
+        let mut src_unaligned = unsafe {
+            UnalignedU16Slice::new(
+                src_remaining.as_ptr(),
+                ::core::cmp::min(src_remaining.len() / 2, dst_remaining.len()),
+            )
+        };
+        if src_unaligned.len() == 0 {
+            return None;
+        }
+        let last_unit = swap_if_opposite_endian::<E>(src_unaligned.at(src_unaligned.len() - 1));
+        if super::in_range16(last_unit, 0xD800, 0xDC00) {
+            // Last code unit is a high surrogate. It might
+            // legitimately form a pair later, so let's not
+            // include it.
+            src_unaligned.trim_last();
+        }
+        let mut offset = 0usize;
+        loop {
+            if let Some((surrogate, bmp_len)) = {
+                let src_left = src_unaligned.tail(offset);
+                let dst_left = &mut dst_remaining[offset..src_unaligned.len()];
+                src_left.copy_bmp_to::<E>(dst_left)
+            } {
+                offset += bmp_len; // surrogate has not been consumed yet
+                let second_pos = offset + 1;
+                if surrogate > 0xDBFF || second_pos == src_unaligned.len() {
+                    // Unpaired surrogate
+                    source.pos += second_pos * 2;
+                    self.pos += offset;
+                    return Some((source.pos, self.pos));
+                }
+                let second = swap_if_opposite_endian::<E>(src_unaligned.at(second_pos));
+                if !super::in_range16(second, 0xDC00, 0xE000) {
+                    // Unpaired surrogate
+                    source.pos += second_pos * 2;
+                    self.pos += offset;
+                    return Some((source.pos, self.pos));
+                }
+                // `surrogate` was already speculatively written
+                dst_remaining[second_pos] = second;
+                offset += 2;
+                continue;
+            } else {
+                source.pos += src_unaligned.len() * 2;
+                self.pos += src_unaligned.len();
+                return None;
+            }
+        }
+    }
+}
+
+// UTF-8 destination
+
+pub struct Utf8BmpHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut Utf8Destination<'b>,
+}
+
+impl<'a, 'b> Utf8BmpHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut Utf8Destination<'b>) -> Utf8BmpHandle<'a, 'b> {
+        Utf8BmpHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_ascii(self, ascii: u8) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_ascii(ascii);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp_excl_ascii(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_bmp_excl_ascii(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_mid_bmp(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_mid_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_upper_bmp(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_upper_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf8Destination<'b> {
+        self.dest
+    }
+}
+
+pub struct Utf8AstralHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut Utf8Destination<'b>,
+}
+
+impl<'a, 'b> Utf8AstralHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut Utf8Destination<'b>) -> Utf8AstralHandle<'a, 'b> {
+        Utf8AstralHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_ascii(self, ascii: u8) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_ascii(ascii);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_bmp_excl_ascii(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_bmp_excl_ascii(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_upper_bmp(self, bmp: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_upper_bmp(bmp);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_astral(self, astral: u32) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_astral(astral);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_surrogate_pair(self, high: u16, low: u16) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_surrogate_pair(high, low);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_big5_combination(
+        self,
+        combined: u16,
+        combining: u16,
+    ) -> &'a mut Utf8Destination<'b> {
+        self.dest.write_big5_combination(combined, combining);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf8Destination<'b> {
+        self.dest
+    }
+}
+
+pub struct Utf8Destination<'a> {
+    slice: &'a mut [u8],
+    pos: usize,
+}
+
+impl<'a> Utf8Destination<'a> {
+    #[inline(always)]
+    pub fn new(dst: &mut [u8]) -> Utf8Destination {
+        Utf8Destination { slice: dst, pos: 0 }
+    }
+    #[inline(always)]
+    pub fn check_space_bmp<'b>(&'b mut self) -> Space<Utf8BmpHandle<'b, 'a>> {
+        if self.pos + 2 < self.slice.len() {
+            Space::Available(Utf8BmpHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn check_space_astral<'b>(&'b mut self) -> Space<Utf8AstralHandle<'b, 'a>> {
+        if self.pos + 3 < self.slice.len() {
+            Space::Available(Utf8AstralHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.pos
+    }
+    #[inline(always)]
+    fn write_code_unit(&mut self, u: u8) {
+        unsafe {
+            // OK, because we checked before handing out a handle.
+            *(self.slice.get_unchecked_mut(self.pos)) = u;
+        }
+        self.pos += 1;
+    }
+    #[inline(always)]
+    fn write_ascii(&mut self, ascii: u8) {
+        debug_assert!(ascii < 0x80);
+        self.write_code_unit(ascii);
+    }
+    #[inline(always)]
+    fn write_bmp(&mut self, bmp: u16) {
+        if bmp < 0x80u16 {
+            self.write_ascii(bmp as u8);
+        } else if bmp < 0x800u16 {
+            self.write_mid_bmp(bmp);
+        } else {
+            self.write_upper_bmp(bmp);
+        }
+    }
+    #[inline(always)]
+    fn write_mid_bmp(&mut self, mid_bmp: u16) {
+        debug_assert!(mid_bmp >= 0x80);
+        debug_assert!(mid_bmp < 0x800);
+        self.write_code_unit(((mid_bmp >> 6) | 0xC0) as u8);
+        self.write_code_unit(((mid_bmp & 0x3F) | 0x80) as u8);
+    }
+    #[inline(always)]
+    fn write_upper_bmp(&mut self, upper_bmp: u16) {
+        debug_assert!(upper_bmp >= 0x800);
+        self.write_code_unit(((upper_bmp >> 12) | 0xE0) as u8);
+        self.write_code_unit((((upper_bmp & 0xFC0) >> 6) | 0x80) as u8);
+        self.write_code_unit(((upper_bmp & 0x3F) | 0x80) as u8);
+    }
+    #[inline(always)]
+    fn write_bmp_excl_ascii(&mut self, bmp: u16) {
+        if bmp < 0x800u16 {
+            self.write_mid_bmp(bmp);
+        } else {
+            self.write_upper_bmp(bmp);
+        }
+    }
+    #[inline(always)]
+    fn write_astral(&mut self, astral: u32) {
+        debug_assert!(astral > 0xFFFF);
+        debug_assert!(astral <= 0x10_FFFF);
+        self.write_code_unit(((astral >> 18) | 0xF0) as u8);
+        self.write_code_unit((((astral & 0x3F000) >> 12) | 0x80) as u8);
+        self.write_code_unit((((astral & 0xFC0) >> 6) | 0x80) as u8);
+        self.write_code_unit(((astral & 0x3F) | 0x80) as u8);
+    }
+    #[inline(always)]
+    pub fn write_surrogate_pair(&mut self, high: u16, low: u16) {
+        self.write_astral(
+            (u32::from(high) << 10) + u32::from(low)
+                - (((0xD800u32 << 10) - 0x10000u32) + 0xDC00u32),
+        );
+    }
+    #[inline(always)]
+    fn write_big5_combination(&mut self, combined: u16, combining: u16) {
+        self.write_mid_bmp(combined);
+        self.write_mid_bmp(combining);
+    }
+    #[inline(always)]
+    pub fn copy_ascii_from_check_space_bmp<'b>(
+        &'b mut self,
+        source: &mut ByteSource,
+    ) -> CopyAsciiResult<(DecoderResult, usize, usize), (u8, Utf8BmpHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = self.slice.len();
+            let src_remaining = &source.slice[source.pos..];
+            let dst_remaining = &mut self.slice[self.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (DecoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (DecoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    source.pos += length;
+                    self.pos += length;
+                    return CopyAsciiResult::Stop((pending, source.pos, self.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    source.pos += consumed;
+                    self.pos += consumed;
+                    if self.pos + 2 < dst_len {
+                        source.pos += 1; // +1 for non_ascii
+                        non_ascii
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            DecoderResult::OutputFull,
+                            source.pos,
+                            self.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, Utf8BmpHandle::new(self)))
+    }
+    #[inline(always)]
+    pub fn copy_ascii_from_check_space_astral<'b>(
+        &'b mut self,
+        source: &mut ByteSource,
+    ) -> CopyAsciiResult<(DecoderResult, usize, usize), (u8, Utf8AstralHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = self.slice.len();
+            let src_remaining = &source.slice[source.pos..];
+            let dst_remaining = &mut self.slice[self.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (DecoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (DecoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    source.pos += length;
+                    self.pos += length;
+                    return CopyAsciiResult::Stop((pending, source.pos, self.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    source.pos += consumed;
+                    self.pos += consumed;
+                    if self.pos + 3 < dst_len {
+                        source.pos += 1; // +1 for non_ascii
+                        non_ascii
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            DecoderResult::OutputFull,
+                            source.pos,
+                            self.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, Utf8AstralHandle::new(self)))
+    }
+    #[inline(always)]
+    pub fn copy_utf8_up_to_invalid_from(&mut self, source: &mut ByteSource) {
+        let src_remaining = &source.slice[source.pos..];
+        let dst_remaining = &mut self.slice[self.pos..];
+        let min_len = ::core::cmp::min(src_remaining.len(), dst_remaining.len());
+        // Validate first, then memcpy to let memcpy do its thing even for
+        // non-ASCII. (And potentially do something better than SSE2 for ASCII.)
+        let valid_len = utf8_valid_up_to(&src_remaining[..min_len]);
+        (&mut dst_remaining[..valid_len]).copy_from_slice(&src_remaining[..valid_len]);
+        source.pos += valid_len;
+        self.pos += valid_len;
+    }
+    #[inline(always)]
+    pub fn copy_utf16_from<E: Endian>(
+        &mut self,
+        source: &mut ByteSource,
+    ) -> Option<(usize, usize)> {
+        let src_remaining = &source.slice[source.pos..];
+        let dst_remaining = &mut self.slice[self.pos..];
+
+        let mut src_unaligned =
+            unsafe { UnalignedU16Slice::new(src_remaining.as_ptr(), src_remaining.len() / 2) };
+        if src_unaligned.len() == 0 {
+            return None;
+        }
+        let mut last_unit = src_unaligned.at(src_unaligned.len() - 1);
+        if E::OPPOSITE_ENDIAN {
+            last_unit = last_unit.swap_bytes();
+        }
+        if super::in_range16(last_unit, 0xD800, 0xDC00) {
+            // Last code unit is a high surrogate. It might
+            // legitimately form a pair later, so let's not
+            // include it.
+            src_unaligned.trim_last();
+        }
+        let (read, written, had_error) =
+            convert_unaligned_utf16_to_utf8::<E>(src_unaligned, dst_remaining);
+        source.pos += read * 2;
+        self.pos += written;
+        if had_error {
+            Some((source.pos, self.pos))
+        } else {
+            None
+        }
+    }
+}
+
+// UTF-16 source
+
+pub struct Utf16Source<'a> {
+    slice: &'a [u16],
+    pos: usize,
+    old_pos: usize,
+}
+
+impl<'a> Utf16Source<'a> {
+    #[inline(always)]
+    pub fn new(src: &[u16]) -> Utf16Source {
+        Utf16Source {
+            slice: src,
+            pos: 0,
+            old_pos: 0,
+        }
+    }
+    #[inline(always)]
+    pub fn check_available<'b>(&'b mut self) -> Space<Utf16ReadHandle<'b, 'a>> {
+        if self.pos < self.slice.len() {
+            Space::Available(Utf16ReadHandle::new(self))
+        } else {
+            Space::Full(self.consumed())
+        }
+    }
+    #[cfg_attr(feature = "cargo-clippy", allow(collapsible_if))]
+    #[inline(always)]
+    fn read(&mut self) -> char {
+        self.old_pos = self.pos;
+        let unit = self.slice[self.pos];
+        self.pos += 1;
+        let unit_minus_surrogate_start = unit.wrapping_sub(0xD800);
+        if unit_minus_surrogate_start > (0xDFFF - 0xD800) {
+            return unsafe { ::core::char::from_u32_unchecked(u32::from(unit)) };
+        }
+        if unit_minus_surrogate_start <= (0xDBFF - 0xD800) {
+            // high surrogate
+            if self.pos < self.slice.len() {
+                let second = self.slice[self.pos];
+                let second_minus_low_surrogate_start = second.wrapping_sub(0xDC00);
+                if second_minus_low_surrogate_start <= (0xDFFF - 0xDC00) {
+                    // The next code unit is a low surrogate. Advance position.
+                    self.pos += 1;
+                    return unsafe {
+                        ::core::char::from_u32_unchecked(
+                            (u32::from(unit) << 10) + u32::from(second)
+                                - (((0xD800u32 << 10) - 0x10000u32) + 0xDC00u32),
+                        )
+                    };
+                }
+                // The next code unit is not a low surrogate. Don't advance
+                // position and treat the high surrogate as unpaired.
+                // fall through
+            }
+            // Unpaired surrogate at the end of buffer, fall through
+        }
+        // Unpaired low surrogate
+        '\u{FFFD}'
+    }
+    #[cfg_attr(feature = "cargo-clippy", allow(collapsible_if))]
+    #[inline(always)]
+    fn read_enum(&mut self) -> Unicode {
+        self.old_pos = self.pos;
+        let unit = self.slice[self.pos];
+        self.pos += 1;
+        if unit < 0x80 {
+            return Unicode::Ascii(unit as u8);
+        }
+        let unit_minus_surrogate_start = unit.wrapping_sub(0xD800);
+        if unit_minus_surrogate_start > (0xDFFF - 0xD800) {
+            return Unicode::NonAscii(NonAscii::BmpExclAscii(unit));
+        }
+        if unit_minus_surrogate_start <= (0xDBFF - 0xD800) {
+            // high surrogate
+            if self.pos < self.slice.len() {
+                let second = self.slice[self.pos];
+                let second_minus_low_surrogate_start = second.wrapping_sub(0xDC00);
+                if second_minus_low_surrogate_start <= (0xDFFF - 0xDC00) {
+                    // The next code unit is a low surrogate. Advance position.
+                    self.pos += 1;
+                    return Unicode::NonAscii(NonAscii::Astral(unsafe {
+                        ::core::char::from_u32_unchecked(
+                            (u32::from(unit) << 10) + u32::from(second)
+                                - (((0xD800u32 << 10) - 0x10000u32) + 0xDC00u32),
+                        )
+                    }));
+                }
+                // The next code unit is not a low surrogate. Don't advance
+                // position and treat the high surrogate as unpaired.
+                // fall through
+            }
+            // Unpaired surrogate at the end of buffer, fall through
+        }
+        // Unpaired low surrogate
+        Unicode::NonAscii(NonAscii::BmpExclAscii(0xFFFDu16))
+    }
+    #[inline(always)]
+    fn unread(&mut self) -> usize {
+        self.pos = self.old_pos;
+        self.pos
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.pos
+    }
+    #[inline(always)]
+    pub fn copy_ascii_to_check_space_two<'b>(
+        &mut self,
+        dest: &'b mut ByteDestination<'a>,
+    ) -> CopyAsciiResult<(EncoderResult, usize, usize), (NonAscii, ByteTwoHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = dest.slice.len();
+            let src_remaining = &self.slice[self.pos..];
+            let dst_remaining = &mut dest.slice[dest.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (EncoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (EncoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                basic_latin_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    self.pos += length;
+                    dest.pos += length;
+                    return CopyAsciiResult::Stop((pending, self.pos, dest.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    self.pos += consumed;
+                    dest.pos += consumed;
+                    if dest.pos + 1 < dst_len {
+                        self.pos += 1; // commit to reading `non_ascii`
+                        let unit = non_ascii;
+                        let unit_minus_surrogate_start = unit.wrapping_sub(0xD800);
+                        if unit_minus_surrogate_start > (0xDFFF - 0xD800) {
+                            NonAscii::BmpExclAscii(unit)
+                        } else if unit_minus_surrogate_start <= (0xDBFF - 0xD800) {
+                            // high surrogate
+                            if self.pos < self.slice.len() {
+                                let second = self.slice[self.pos];
+                                let second_minus_low_surrogate_start = second.wrapping_sub(0xDC00);
+                                if second_minus_low_surrogate_start <= (0xDFFF - 0xDC00) {
+                                    // The next code unit is a low surrogate. Advance position.
+                                    self.pos += 1;
+                                    NonAscii::Astral(unsafe {
+                                        ::core::char::from_u32_unchecked(
+                                            (u32::from(unit) << 10) + u32::from(second)
+                                                - (((0xD800u32 << 10) - 0x10000u32) + 0xDC00u32),
+                                        )
+                                    })
+                                } else {
+                                    // The next code unit is not a low surrogate. Don't advance
+                                    // position and treat the high surrogate as unpaired.
+                                    NonAscii::BmpExclAscii(0xFFFDu16)
+                                }
+                            } else {
+                                // Unpaired surrogate at the end of the buffer.
+                                NonAscii::BmpExclAscii(0xFFFDu16)
+                            }
+                        } else {
+                            // Unpaired low surrogate
+                            NonAscii::BmpExclAscii(0xFFFDu16)
+                        }
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            EncoderResult::OutputFull,
+                            self.pos,
+                            dest.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, ByteTwoHandle::new(dest)))
+    }
+    #[inline(always)]
+    pub fn copy_ascii_to_check_space_four<'b>(
+        &mut self,
+        dest: &'b mut ByteDestination<'a>,
+    ) -> CopyAsciiResult<(EncoderResult, usize, usize), (NonAscii, ByteFourHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = dest.slice.len();
+            let src_remaining = &self.slice[self.pos..];
+            let dst_remaining = &mut dest.slice[dest.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (EncoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (EncoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                basic_latin_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    self.pos += length;
+                    dest.pos += length;
+                    return CopyAsciiResult::Stop((pending, self.pos, dest.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    self.pos += consumed;
+                    dest.pos += consumed;
+                    if dest.pos + 3 < dst_len {
+                        self.pos += 1; // commit to reading `non_ascii`
+                        let unit = non_ascii;
+                        let unit_minus_surrogate_start = unit.wrapping_sub(0xD800);
+                        if unit_minus_surrogate_start > (0xDFFF - 0xD800) {
+                            NonAscii::BmpExclAscii(unit)
+                        } else if unit_minus_surrogate_start <= (0xDBFF - 0xD800) {
+                            // high surrogate
+                            if self.pos == self.slice.len() {
+                                // Unpaired surrogate at the end of the buffer.
+                                NonAscii::BmpExclAscii(0xFFFDu16)
+                            } else {
+                                let second = self.slice[self.pos];
+                                let second_minus_low_surrogate_start = second.wrapping_sub(0xDC00);
+                                if second_minus_low_surrogate_start <= (0xDFFF - 0xDC00) {
+                                    // The next code unit is a low surrogate. Advance position.
+                                    self.pos += 1;
+                                    NonAscii::Astral(unsafe {
+                                        ::core::char::from_u32_unchecked(
+                                            (u32::from(unit) << 10) + u32::from(second)
+                                                - (((0xD800u32 << 10) - 0x1_0000u32) + 0xDC00u32),
+                                        )
+                                    })
+                                } else {
+                                    // The next code unit is not a low surrogate. Don't advance
+                                    // position and treat the high surrogate as unpaired.
+                                    NonAscii::BmpExclAscii(0xFFFDu16)
+                                }
+                            }
+                        } else {
+                            // Unpaired low surrogate
+                            NonAscii::BmpExclAscii(0xFFFDu16)
+                        }
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            EncoderResult::OutputFull,
+                            self.pos,
+                            dest.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, ByteFourHandle::new(dest)))
+    }
+}
+
+pub struct Utf16ReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut Utf16Source<'b>,
+}
+
+impl<'a, 'b> Utf16ReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut Utf16Source<'b>) -> Utf16ReadHandle<'a, 'b> {
+        Utf16ReadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn read(self) -> (char, Utf16UnreadHandle<'a, 'b>) {
+        let character = self.source.read();
+        let handle = Utf16UnreadHandle::new(self.source);
+        (character, handle)
+    }
+    #[inline(always)]
+    pub fn read_enum(self) -> (Unicode, Utf16UnreadHandle<'a, 'b>) {
+        let character = self.source.read_enum();
+        let handle = Utf16UnreadHandle::new(self.source);
+        (character, handle)
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+}
+
+pub struct Utf16UnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut Utf16Source<'b>,
+}
+
+impl<'a, 'b> Utf16UnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut Utf16Source<'b>) -> Utf16UnreadHandle<'a, 'b> {
+        Utf16UnreadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn unread(self) -> usize {
+        self.source.unread()
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf16Source<'b> {
+        self.source
+    }
+}
+
+// UTF-8 source
+
+pub struct Utf8Source<'a> {
+    slice: &'a [u8],
+    pos: usize,
+    old_pos: usize,
+}
+
+impl<'a> Utf8Source<'a> {
+    #[inline(always)]
+    pub fn new(src: &str) -> Utf8Source {
+        Utf8Source {
+            slice: src.as_bytes(),
+            pos: 0,
+            old_pos: 0,
+        }
+    }
+    #[inline(always)]
+    pub fn check_available<'b>(&'b mut self) -> Space<Utf8ReadHandle<'b, 'a>> {
+        if self.pos < self.slice.len() {
+            Space::Available(Utf8ReadHandle::new(self))
+        } else {
+            Space::Full(self.consumed())
+        }
+    }
+    #[inline(always)]
+    fn read(&mut self) -> char {
+        self.old_pos = self.pos;
+        let unit = self.slice[self.pos];
+        if unit < 0x80 {
+            self.pos += 1;
+            return char::from(unit);
+        }
+        if unit < 0xE0 {
+            let point =
+                ((u32::from(unit) & 0x1F) << 6) | (u32::from(self.slice[self.pos + 1]) & 0x3F);
+            self.pos += 2;
+            return unsafe { ::core::char::from_u32_unchecked(point) };
+        }
+        if unit < 0xF0 {
+            let point = ((u32::from(unit) & 0xF) << 12)
+                | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 6)
+                | (u32::from(self.slice[self.pos + 2]) & 0x3F);
+            self.pos += 3;
+            return unsafe { ::core::char::from_u32_unchecked(point) };
+        }
+        let point = ((u32::from(unit) & 0x7) << 18)
+            | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 12)
+            | ((u32::from(self.slice[self.pos + 2]) & 0x3F) << 6)
+            | (u32::from(self.slice[self.pos + 3]) & 0x3F);
+        self.pos += 4;
+        unsafe { ::core::char::from_u32_unchecked(point) }
+    }
+    #[inline(always)]
+    fn read_enum(&mut self) -> Unicode {
+        self.old_pos = self.pos;
+        let unit = self.slice[self.pos];
+        if unit < 0x80 {
+            self.pos += 1;
+            return Unicode::Ascii(unit);
+        }
+        if unit < 0xE0 {
+            let point =
+                ((u16::from(unit) & 0x1F) << 6) | (u16::from(self.slice[self.pos + 1]) & 0x3F);
+            self.pos += 2;
+            return Unicode::NonAscii(NonAscii::BmpExclAscii(point));
+        }
+        if unit < 0xF0 {
+            let point = ((u16::from(unit) & 0xF) << 12)
+                | ((u16::from(self.slice[self.pos + 1]) & 0x3F) << 6)
+                | (u16::from(self.slice[self.pos + 2]) & 0x3F);
+            self.pos += 3;
+            return Unicode::NonAscii(NonAscii::BmpExclAscii(point));
+        }
+        let point = ((u32::from(unit) & 0x7) << 18)
+            | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 12)
+            | ((u32::from(self.slice[self.pos + 2]) & 0x3F) << 6)
+            | (u32::from(self.slice[self.pos + 3]) & 0x3F);
+        self.pos += 4;
+        Unicode::NonAscii(NonAscii::Astral(unsafe {
+            ::core::char::from_u32_unchecked(point)
+        }))
+    }
+    #[inline(always)]
+    fn unread(&mut self) -> usize {
+        self.pos = self.old_pos;
+        self.pos
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.pos
+    }
+    #[inline(always)]
+    pub fn copy_ascii_to_check_space_one<'b>(
+        &mut self,
+        dest: &'b mut ByteDestination<'a>,
+    ) -> CopyAsciiResult<(EncoderResult, usize, usize), (NonAscii, ByteOneHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let src_remaining = &self.slice[self.pos..];
+            let dst_remaining = &mut dest.slice[dest.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (EncoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (EncoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    self.pos += length;
+                    dest.pos += length;
+                    return CopyAsciiResult::Stop((pending, self.pos, dest.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    self.pos += consumed;
+                    dest.pos += consumed;
+                    // We don't need to check space in destination, because
+                    // `ascii_to_ascii()` already did.
+                    if non_ascii < 0xE0 {
+                        let point = ((u16::from(non_ascii) & 0x1F) << 6)
+                            | (u16::from(self.slice[self.pos + 1]) & 0x3F);
+                        self.pos += 2;
+                        NonAscii::BmpExclAscii(point)
+                    } else if non_ascii < 0xF0 {
+                        let point = ((u16::from(non_ascii) & 0xF) << 12)
+                            | ((u16::from(self.slice[self.pos + 1]) & 0x3F) << 6)
+                            | (u16::from(self.slice[self.pos + 2]) & 0x3F);
+                        self.pos += 3;
+                        NonAscii::BmpExclAscii(point)
+                    } else {
+                        let point = ((u32::from(non_ascii) & 0x7) << 18)
+                            | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 12)
+                            | ((u32::from(self.slice[self.pos + 2]) & 0x3F) << 6)
+                            | (u32::from(self.slice[self.pos + 3]) & 0x3F);
+                        self.pos += 4;
+                        NonAscii::Astral(unsafe { ::core::char::from_u32_unchecked(point) })
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, ByteOneHandle::new(dest)))
+    }
+    #[inline(always)]
+    pub fn copy_ascii_to_check_space_two<'b>(
+        &mut self,
+        dest: &'b mut ByteDestination<'a>,
+    ) -> CopyAsciiResult<(EncoderResult, usize, usize), (NonAscii, ByteTwoHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = dest.slice.len();
+            let src_remaining = &self.slice[self.pos..];
+            let dst_remaining = &mut dest.slice[dest.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (EncoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (EncoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    self.pos += length;
+                    dest.pos += length;
+                    return CopyAsciiResult::Stop((pending, self.pos, dest.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    self.pos += consumed;
+                    dest.pos += consumed;
+                    if dest.pos + 1 < dst_len {
+                        if non_ascii < 0xE0 {
+                            let point = ((u16::from(non_ascii) & 0x1F) << 6)
+                                | (u16::from(self.slice[self.pos + 1]) & 0x3F);
+                            self.pos += 2;
+                            NonAscii::BmpExclAscii(point)
+                        } else if non_ascii < 0xF0 {
+                            let point = ((u16::from(non_ascii) & 0xF) << 12)
+                                | ((u16::from(self.slice[self.pos + 1]) & 0x3F) << 6)
+                                | (u16::from(self.slice[self.pos + 2]) & 0x3F);
+                            self.pos += 3;
+                            NonAscii::BmpExclAscii(point)
+                        } else {
+                            let point = ((u32::from(non_ascii) & 0x7) << 18)
+                                | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 12)
+                                | ((u32::from(self.slice[self.pos + 2]) & 0x3F) << 6)
+                                | (u32::from(self.slice[self.pos + 3]) & 0x3F);
+                            self.pos += 4;
+                            NonAscii::Astral(unsafe { ::core::char::from_u32_unchecked(point) })
+                        }
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            EncoderResult::OutputFull,
+                            self.pos,
+                            dest.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, ByteTwoHandle::new(dest)))
+    }
+    #[inline(always)]
+    pub fn copy_ascii_to_check_space_four<'b>(
+        &mut self,
+        dest: &'b mut ByteDestination<'a>,
+    ) -> CopyAsciiResult<(EncoderResult, usize, usize), (NonAscii, ByteFourHandle<'b, 'a>)> {
+        let non_ascii_ret = {
+            let dst_len = dest.slice.len();
+            let src_remaining = &self.slice[self.pos..];
+            let dst_remaining = &mut dest.slice[dest.pos..];
+            let (pending, length) = if dst_remaining.len() < src_remaining.len() {
+                (EncoderResult::OutputFull, dst_remaining.len())
+            } else {
+                (EncoderResult::InputEmpty, src_remaining.len())
+            };
+            match unsafe {
+                ascii_to_ascii(src_remaining.as_ptr(), dst_remaining.as_mut_ptr(), length)
+            } {
+                None => {
+                    self.pos += length;
+                    dest.pos += length;
+                    return CopyAsciiResult::Stop((pending, self.pos, dest.pos));
+                }
+                Some((non_ascii, consumed)) => {
+                    self.pos += consumed;
+                    dest.pos += consumed;
+                    if dest.pos + 3 < dst_len {
+                        if non_ascii < 0xE0 {
+                            let point = ((u16::from(non_ascii) & 0x1F) << 6)
+                                | (u16::from(self.slice[self.pos + 1]) & 0x3F);
+                            self.pos += 2;
+                            NonAscii::BmpExclAscii(point)
+                        } else if non_ascii < 0xF0 {
+                            let point = ((u16::from(non_ascii) & 0xF) << 12)
+                                | ((u16::from(self.slice[self.pos + 1]) & 0x3F) << 6)
+                                | (u16::from(self.slice[self.pos + 2]) & 0x3F);
+                            self.pos += 3;
+                            NonAscii::BmpExclAscii(point)
+                        } else {
+                            let point = ((u32::from(non_ascii) & 0x7) << 18)
+                                | ((u32::from(self.slice[self.pos + 1]) & 0x3F) << 12)
+                                | ((u32::from(self.slice[self.pos + 2]) & 0x3F) << 6)
+                                | (u32::from(self.slice[self.pos + 3]) & 0x3F);
+                            self.pos += 4;
+                            NonAscii::Astral(unsafe { ::core::char::from_u32_unchecked(point) })
+                        }
+                    } else {
+                        return CopyAsciiResult::Stop((
+                            EncoderResult::OutputFull,
+                            self.pos,
+                            dest.pos,
+                        ));
+                    }
+                }
+            }
+        };
+        CopyAsciiResult::GoOn((non_ascii_ret, ByteFourHandle::new(dest)))
+    }
+}
+
+pub struct Utf8ReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut Utf8Source<'b>,
+}
+
+impl<'a, 'b> Utf8ReadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut Utf8Source<'b>) -> Utf8ReadHandle<'a, 'b> {
+        Utf8ReadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn read(self) -> (char, Utf8UnreadHandle<'a, 'b>) {
+        let character = self.source.read();
+        let handle = Utf8UnreadHandle::new(self.source);
+        (character, handle)
+    }
+    #[inline(always)]
+    pub fn read_enum(self) -> (Unicode, Utf8UnreadHandle<'a, 'b>) {
+        let character = self.source.read_enum();
+        let handle = Utf8UnreadHandle::new(self.source);
+        (character, handle)
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+}
+
+pub struct Utf8UnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    source: &'a mut Utf8Source<'b>,
+}
+
+impl<'a, 'b> Utf8UnreadHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(src: &'a mut Utf8Source<'b>) -> Utf8UnreadHandle<'a, 'b> {
+        Utf8UnreadHandle { source: src }
+    }
+    #[inline(always)]
+    pub fn unread(self) -> usize {
+        self.source.unread()
+    }
+    #[inline(always)]
+    pub fn consumed(&self) -> usize {
+        self.source.consumed()
+    }
+    #[inline(always)]
+    pub fn commit(self) -> &'a mut Utf8Source<'b> {
+        self.source
+    }
+}
+
+// Byte destination
+
+pub struct ByteOneHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut ByteDestination<'b>,
+}
+
+impl<'a, 'b> ByteOneHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut ByteDestination<'b>) -> ByteOneHandle<'a, 'b> {
+        ByteOneHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_one(self, first: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_one(first);
+        self.dest
+    }
+}
+
+pub struct ByteTwoHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut ByteDestination<'b>,
+}
+
+impl<'a, 'b> ByteTwoHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut ByteDestination<'b>) -> ByteTwoHandle<'a, 'b> {
+        ByteTwoHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_one(self, first: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_one(first);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_two(self, first: u8, second: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_two(first, second);
+        self.dest
+    }
+}
+
+pub struct ByteThreeHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut ByteDestination<'b>,
+}
+
+impl<'a, 'b> ByteThreeHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut ByteDestination<'b>) -> ByteThreeHandle<'a, 'b> {
+        ByteThreeHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_one(self, first: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_one(first);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_two(self, first: u8, second: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_two(first, second);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_three(self, first: u8, second: u8, third: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_three(first, second, third);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_three_return_written(self, first: u8, second: u8, third: u8) -> usize {
+        self.dest.write_three(first, second, third);
+        self.dest.written()
+    }
+}
+
+pub struct ByteFourHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    dest: &'a mut ByteDestination<'b>,
+}
+
+impl<'a, 'b> ByteFourHandle<'a, 'b>
+where
+    'b: 'a,
+{
+    #[inline(always)]
+    fn new(dst: &'a mut ByteDestination<'b>) -> ByteFourHandle<'a, 'b> {
+        ByteFourHandle { dest: dst }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.dest.written()
+    }
+    #[inline(always)]
+    pub fn write_one(self, first: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_one(first);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_two(self, first: u8, second: u8) -> &'a mut ByteDestination<'b> {
+        self.dest.write_two(first, second);
+        self.dest
+    }
+    #[inline(always)]
+    pub fn write_four(
+        self,
+        first: u8,
+        second: u8,
+        third: u8,
+        fourth: u8,
+    ) -> &'a mut ByteDestination<'b> {
+        self.dest.write_four(first, second, third, fourth);
+        self.dest
+    }
+}
+
+pub struct ByteDestination<'a> {
+    slice: &'a mut [u8],
+    pos: usize,
+}
+
+impl<'a> ByteDestination<'a> {
+    #[inline(always)]
+    pub fn new(dst: &mut [u8]) -> ByteDestination {
+        ByteDestination { slice: dst, pos: 0 }
+    }
+    #[inline(always)]
+    pub fn check_space_one<'b>(&'b mut self) -> Space<ByteOneHandle<'b, 'a>> {
+        if self.pos < self.slice.len() {
+            Space::Available(ByteOneHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn check_space_two<'b>(&'b mut self) -> Space<ByteTwoHandle<'b, 'a>> {
+        if self.pos + 1 < self.slice.len() {
+            Space::Available(ByteTwoHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn check_space_three<'b>(&'b mut self) -> Space<ByteThreeHandle<'b, 'a>> {
+        if self.pos + 2 < self.slice.len() {
+            Space::Available(ByteThreeHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn check_space_four<'b>(&'b mut self) -> Space<ByteFourHandle<'b, 'a>> {
+        if self.pos + 3 < self.slice.len() {
+            Space::Available(ByteFourHandle::new(self))
+        } else {
+            Space::Full(self.written())
+        }
+    }
+    #[inline(always)]
+    pub fn written(&self) -> usize {
+        self.pos
+    }
+    #[inline(always)]
+    fn write_one(&mut self, first: u8) {
+        self.slice[self.pos] = first;
+        self.pos += 1;
+    }
+    #[inline(always)]
+    fn write_two(&mut self, first: u8, second: u8) {
+        self.slice[self.pos] = first;
+        self.slice[self.pos + 1] = second;
+        self.pos += 2;
+    }
+    #[inline(always)]
+    fn write_three(&mut self, first: u8, second: u8, third: u8) {
+        self.slice[self.pos] = first;
+        self.slice[self.pos + 1] = second;
+        self.slice[self.pos + 2] = third;
+        self.pos += 3;
+    }
+    #[inline(always)]
+    fn write_four(&mut self, first: u8, second: u8, third: u8, fourth: u8) {
+        self.slice[self.pos] = first;
+        self.slice[self.pos + 1] = second;
+        self.slice[self.pos + 2] = third;
+        self.slice[self.pos + 3] = fourth;
+        self.pos += 4;
+    }
+}