From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 19 Apr 2024 02:47:55 +0200 Subject: Adding upstream version 124.0.1. Signed-off-by: Daniel Baumann --- third_party/rust/hashbrown/src/raw/generic.rs | 154 ++++++++++++++++++++++++++ 1 file changed, 154 insertions(+) create mode 100644 third_party/rust/hashbrown/src/raw/generic.rs (limited to 'third_party/rust/hashbrown/src/raw/generic.rs') diff --git a/third_party/rust/hashbrown/src/raw/generic.rs b/third_party/rust/hashbrown/src/raw/generic.rs new file mode 100644 index 0000000000..b4d31e62c2 --- /dev/null +++ b/third_party/rust/hashbrown/src/raw/generic.rs @@ -0,0 +1,154 @@ +use super::bitmask::BitMask; +use super::EMPTY; +use core::{mem, ptr}; + +// Use the native word size as the group size. Using a 64-bit group size on +// a 32-bit architecture will just end up being more expensive because +// shifts and multiplies will need to be emulated. +#[cfg(any( + target_pointer_width = "64", + target_arch = "aarch64", + target_arch = "x86_64", + target_arch = "wasm32", +))] +type GroupWord = u64; +#[cfg(all( + target_pointer_width = "32", + not(target_arch = "aarch64"), + not(target_arch = "x86_64"), + not(target_arch = "wasm32"), +))] +type GroupWord = u32; + +pub type BitMaskWord = GroupWord; +pub const BITMASK_STRIDE: usize = 8; +// We only care about the highest bit of each byte for the mask. +#[allow(clippy::cast_possible_truncation, clippy::unnecessary_cast)] +pub const BITMASK_MASK: BitMaskWord = 0x8080_8080_8080_8080_u64 as GroupWord; + +/// Helper function to replicate a byte across a `GroupWord`. +#[inline] +fn repeat(byte: u8) -> GroupWord { + GroupWord::from_ne_bytes([byte; Group::WIDTH]) +} + +/// Abstraction over a group of control bytes which can be scanned in +/// parallel. +/// +/// This implementation uses a word-sized integer. +#[derive(Copy, Clone)] +pub struct Group(GroupWord); + +// We perform all operations in the native endianness, and convert to +// little-endian just before creating a BitMask. The can potentially +// enable the compiler to eliminate unnecessary byte swaps if we are +// only checking whether a BitMask is empty. +#[allow(clippy::use_self)] +impl Group { + /// Number of bytes in the group. + pub const WIDTH: usize = mem::size_of::(); + + /// Returns a full group of empty bytes, suitable for use as the initial + /// value for an empty hash table. + /// + /// This is guaranteed to be aligned to the group size. + #[inline] + pub const fn static_empty() -> &'static [u8; Group::WIDTH] { + #[repr(C)] + struct AlignedBytes { + _align: [Group; 0], + bytes: [u8; Group::WIDTH], + } + const ALIGNED_BYTES: AlignedBytes = AlignedBytes { + _align: [], + bytes: [EMPTY; Group::WIDTH], + }; + &ALIGNED_BYTES.bytes + } + + /// Loads a group of bytes starting at the given address. + #[inline] + #[allow(clippy::cast_ptr_alignment)] // unaligned load + pub unsafe fn load(ptr: *const u8) -> Self { + Group(ptr::read_unaligned(ptr.cast())) + } + + /// Loads a group of bytes starting at the given address, which must be + /// aligned to `mem::align_of::()`. + #[inline] + #[allow(clippy::cast_ptr_alignment)] + pub unsafe fn load_aligned(ptr: *const u8) -> Self { + // FIXME: use align_offset once it stabilizes + debug_assert_eq!(ptr as usize & (mem::align_of::() - 1), 0); + Group(ptr::read(ptr.cast())) + } + + /// Stores the group of bytes to the given address, which must be + /// aligned to `mem::align_of::()`. + #[inline] + #[allow(clippy::cast_ptr_alignment)] + pub unsafe fn store_aligned(self, ptr: *mut u8) { + // FIXME: use align_offset once it stabilizes + debug_assert_eq!(ptr as usize & (mem::align_of::() - 1), 0); + ptr::write(ptr.cast(), self.0); + } + + /// Returns a `BitMask` indicating all bytes in the group which *may* + /// have the given value. + /// + /// This function may return a false positive in certain cases where + /// the byte in the group differs from the searched value only in its + /// lowest bit. This is fine because: + /// - This never happens for `EMPTY` and `DELETED`, only full entries. + /// - The check for key equality will catch these. + /// - This only happens if there is at least 1 true match. + /// - The chance of this happening is very low (< 1% chance per byte). + #[inline] + pub fn match_byte(self, byte: u8) -> BitMask { + // This algorithm is derived from + // https://graphics.stanford.edu/~seander/bithacks.html##ValueInWord + let cmp = self.0 ^ repeat(byte); + BitMask((cmp.wrapping_sub(repeat(0x01)) & !cmp & repeat(0x80)).to_le()) + } + + /// Returns a `BitMask` indicating all bytes in the group which are + /// `EMPTY`. + #[inline] + pub fn match_empty(self) -> BitMask { + // If the high bit is set, then the byte must be either: + // 1111_1111 (EMPTY) or 1000_0000 (DELETED). + // So we can just check if the top two bits are 1 by ANDing them. + BitMask((self.0 & (self.0 << 1) & repeat(0x80)).to_le()) + } + + /// Returns a `BitMask` indicating all bytes in the group which are + /// `EMPTY` or `DELETED`. + #[inline] + pub fn match_empty_or_deleted(self) -> BitMask { + // A byte is EMPTY or DELETED iff the high bit is set + BitMask((self.0 & repeat(0x80)).to_le()) + } + + /// Returns a `BitMask` indicating all bytes in the group which are full. + #[inline] + pub fn match_full(self) -> BitMask { + self.match_empty_or_deleted().invert() + } + + /// Performs the following transformation on all bytes in the group: + /// - `EMPTY => EMPTY` + /// - `DELETED => EMPTY` + /// - `FULL => DELETED` + #[inline] + pub fn convert_special_to_empty_and_full_to_deleted(self) -> Self { + // Map high_bit = 1 (EMPTY or DELETED) to 1111_1111 + // and high_bit = 0 (FULL) to 1000_0000 + // + // Here's this logic expanded to concrete values: + // let full = 1000_0000 (true) or 0000_0000 (false) + // !1000_0000 + 1 = 0111_1111 + 1 = 1000_0000 (no carry) + // !0000_0000 + 0 = 1111_1111 + 0 = 1111_1111 (no carry) + let full = !self.0 & repeat(0x80); + Group(!full + (full >> 7)) + } +} -- cgit v1.2.3