diff options
Diffstat (limited to 'library/core/src/num/dec2flt/common.rs')
| -rw-r--r-- | library/core/src/num/dec2flt/common.rs | 198 |
1 files changed, 198 insertions, 0 deletions
diff --git a/library/core/src/num/dec2flt/common.rs b/library/core/src/num/dec2flt/common.rs new file mode 100644 index 000000000..17957d7e7 --- /dev/null +++ b/library/core/src/num/dec2flt/common.rs @@ -0,0 +1,198 @@ +//! Common utilities, for internal use only. + +use crate::ptr; + +/// Helper methods to process immutable bytes. +pub(crate) trait ByteSlice: AsRef<[u8]> { + unsafe fn first_unchecked(&self) -> u8 { + debug_assert!(!self.is_empty()); + // SAFETY: safe as long as self is not empty + unsafe { *self.as_ref().get_unchecked(0) } + } + + /// Get if the slice contains no elements. + fn is_empty(&self) -> bool { + self.as_ref().is_empty() + } + + /// Check if the slice at least `n` length. + fn check_len(&self, n: usize) -> bool { + n <= self.as_ref().len() + } + + /// Check if the first character in the slice is equal to c. + fn first_is(&self, c: u8) -> bool { + self.as_ref().first() == Some(&c) + } + + /// Check if the first character in the slice is equal to c1 or c2. + fn first_is2(&self, c1: u8, c2: u8) -> bool { + if let Some(&c) = self.as_ref().first() { c == c1 || c == c2 } else { false } + } + + /// Bounds-checked test if the first character in the slice is a digit. + fn first_isdigit(&self) -> bool { + if let Some(&c) = self.as_ref().first() { c.is_ascii_digit() } else { false } + } + + /// Check if self starts with u with a case-insensitive comparison. + fn starts_with_ignore_case(&self, u: &[u8]) -> bool { + debug_assert!(self.as_ref().len() >= u.len()); + let iter = self.as_ref().iter().zip(u.iter()); + let d = iter.fold(0, |i, (&x, &y)| i | (x ^ y)); + d == 0 || d == 32 + } + + /// Get the remaining slice after the first N elements. + fn advance(&self, n: usize) -> &[u8] { + &self.as_ref()[n..] + } + + /// Get the slice after skipping all leading characters equal c. + fn skip_chars(&self, c: u8) -> &[u8] { + let mut s = self.as_ref(); + while s.first_is(c) { + s = s.advance(1); + } + s + } + + /// Get the slice after skipping all leading characters equal c1 or c2. + fn skip_chars2(&self, c1: u8, c2: u8) -> &[u8] { + let mut s = self.as_ref(); + while s.first_is2(c1, c2) { + s = s.advance(1); + } + s + } + + /// Read 8 bytes as a 64-bit integer in little-endian order. + unsafe fn read_u64_unchecked(&self) -> u64 { + debug_assert!(self.check_len(8)); + let src = self.as_ref().as_ptr() as *const u64; + // SAFETY: safe as long as self is at least 8 bytes + u64::from_le(unsafe { ptr::read_unaligned(src) }) + } + + /// Try to read the next 8 bytes from the slice. + fn read_u64(&self) -> Option<u64> { + if self.check_len(8) { + // SAFETY: self must be at least 8 bytes. + Some(unsafe { self.read_u64_unchecked() }) + } else { + None + } + } + + /// Calculate the offset of slice from another. + fn offset_from(&self, other: &Self) -> isize { + other.as_ref().len() as isize - self.as_ref().len() as isize + } +} + +impl ByteSlice for [u8] {} + +/// Helper methods to process mutable bytes. +pub(crate) trait ByteSliceMut: AsMut<[u8]> { + /// Write a 64-bit integer as 8 bytes in little-endian order. + unsafe fn write_u64_unchecked(&mut self, value: u64) { + debug_assert!(self.as_mut().len() >= 8); + let dst = self.as_mut().as_mut_ptr() as *mut u64; + // NOTE: we must use `write_unaligned`, since dst is not + // guaranteed to be properly aligned. Miri will warn us + // if we use `write` instead of `write_unaligned`, as expected. + // SAFETY: safe as long as self is at least 8 bytes + unsafe { + ptr::write_unaligned(dst, u64::to_le(value)); + } + } +} + +impl ByteSliceMut for [u8] {} + +/// Bytes wrapper with specialized methods for ASCII characters. +#[derive(Debug, Clone, Copy, PartialEq, Eq)] +pub(crate) struct AsciiStr<'a> { + slc: &'a [u8], +} + +impl<'a> AsciiStr<'a> { + pub fn new(slc: &'a [u8]) -> Self { + Self { slc } + } + + /// Advance the view by n, advancing it in-place to (n..). + pub unsafe fn step_by(&mut self, n: usize) -> &mut Self { + // SAFETY: safe as long n is less than the buffer length + self.slc = unsafe { self.slc.get_unchecked(n..) }; + self + } + + /// Advance the view by n, advancing it in-place to (1..). + pub unsafe fn step(&mut self) -> &mut Self { + // SAFETY: safe as long as self is not empty + unsafe { self.step_by(1) } + } + + /// Iteratively parse and consume digits from bytes. + pub fn parse_digits(&mut self, mut func: impl FnMut(u8)) { + while let Some(&c) = self.as_ref().first() { + let c = c.wrapping_sub(b'0'); + if c < 10 { + func(c); + // SAFETY: self cannot be empty + unsafe { + self.step(); + } + } else { + break; + } + } + } +} + +impl<'a> AsRef<[u8]> for AsciiStr<'a> { + #[inline] + fn as_ref(&self) -> &[u8] { + self.slc + } +} + +impl<'a> ByteSlice for AsciiStr<'a> {} + +/// Determine if 8 bytes are all decimal digits. +/// This does not care about the order in which the bytes were loaded. +pub(crate) fn is_8digits(v: u64) -> bool { + let a = v.wrapping_add(0x4646_4646_4646_4646); + let b = v.wrapping_sub(0x3030_3030_3030_3030); + (a | b) & 0x8080_8080_8080_8080 == 0 +} + +/// Iteratively parse and consume digits from bytes. +pub(crate) fn parse_digits(s: &mut &[u8], mut f: impl FnMut(u8)) { + while let Some(&c) = s.get(0) { + let c = c.wrapping_sub(b'0'); + if c < 10 { + f(c); + *s = s.advance(1); + } else { + break; + } + } +} + +/// A custom 64-bit floating point type, representing `f * 2^e`. +/// e is biased, so it be directly shifted into the exponent bits. +#[derive(Debug, Copy, Clone, PartialEq, Eq, Default)] +pub struct BiasedFp { + /// The significant digits. + pub f: u64, + /// The biased, binary exponent. + pub e: i32, +} + +impl BiasedFp { + pub const fn zero_pow2(e: i32) -> Self { + Self { f: 0, e } + } +} |