228 lines
6.9 KiB
Rust
228 lines
6.9 KiB
Rust
// Vendored from libstd:
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// https://github.com/rust-lang/rust/blob/1.57.0/library/core/src/hash/sip.rs
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//
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// TODO: maybe depend on a hasher from crates.io if this becomes annoying to
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// maintain, or change this to a simpler one.
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#![cfg(not(feature = "std"))]
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use core::cmp;
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use core::hash::Hasher;
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use core::mem;
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use core::ptr;
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/// An implementation of SipHash 1-3.
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///
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/// This is currently the default hashing function used by standard library
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/// (e.g., `collections::HashMap` uses it by default).
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///
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/// See: <https://131002.net/siphash>
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pub struct SipHasher13 {
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k0: u64,
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k1: u64,
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length: usize, // how many bytes we've processed
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state: State, // hash State
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tail: u64, // unprocessed bytes le
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ntail: usize, // how many bytes in tail are valid
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}
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#[derive(Clone, Copy)]
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#[repr(C)]
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struct State {
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// v0, v2 and v1, v3 show up in pairs in the algorithm,
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// and simd implementations of SipHash will use vectors
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// of v02 and v13. By placing them in this order in the struct,
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// the compiler can pick up on just a few simd optimizations by itself.
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v0: u64,
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v2: u64,
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v1: u64,
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v3: u64,
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}
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macro_rules! compress {
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($state:expr) => {
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compress!($state.v0, $state.v1, $state.v2, $state.v3)
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};
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($v0:expr, $v1:expr, $v2:expr, $v3:expr) => {
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$v0 = $v0.wrapping_add($v1);
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$v1 = $v1.rotate_left(13);
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$v1 ^= $v0;
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$v0 = $v0.rotate_left(32);
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$v2 = $v2.wrapping_add($v3);
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$v3 = $v3.rotate_left(16);
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$v3 ^= $v2;
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$v0 = $v0.wrapping_add($v3);
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$v3 = $v3.rotate_left(21);
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$v3 ^= $v0;
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$v2 = $v2.wrapping_add($v1);
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$v1 = $v1.rotate_left(17);
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$v1 ^= $v2;
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$v2 = $v2.rotate_left(32);
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};
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}
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/// Loads an integer of the desired type from a byte stream, in LE order. Uses
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/// `copy_nonoverlapping` to let the compiler generate the most efficient way
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/// to load it from a possibly unaligned address.
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///
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/// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
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macro_rules! load_int_le {
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($buf:expr, $i:expr, $int_ty:ident) => {{
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debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
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let mut data = 0 as $int_ty;
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ptr::copy_nonoverlapping(
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$buf.as_ptr().add($i),
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&mut data as *mut _ as *mut u8,
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mem::size_of::<$int_ty>(),
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);
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data.to_le()
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}};
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}
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/// Loads a u64 using up to 7 bytes of a byte slice. It looks clumsy but the
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/// `copy_nonoverlapping` calls that occur (via `load_int_le!`) all have fixed
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/// sizes and avoid calling `memcpy`, which is good for speed.
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///
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/// Unsafe because: unchecked indexing at start..start+len
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unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
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debug_assert!(len < 8);
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let mut i = 0; // current byte index (from LSB) in the output u64
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let mut out = 0;
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if i + 3 < len {
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// SAFETY: `i` cannot be greater than `len`, and the caller must guarantee
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// that the index start..start+len is in bounds.
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out = unsafe { load_int_le!(buf, start + i, u32) } as u64;
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i += 4;
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}
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if i + 1 < len {
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// SAFETY: same as above.
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out |= (unsafe { load_int_le!(buf, start + i, u16) } as u64) << (i * 8);
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i += 2
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}
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if i < len {
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// SAFETY: same as above.
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out |= (unsafe { *buf.get_unchecked(start + i) } as u64) << (i * 8);
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i += 1;
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}
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debug_assert_eq!(i, len);
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out
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}
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impl SipHasher13 {
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/// Creates a new `SipHasher13` with the two initial keys set to 0.
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pub fn new() -> Self {
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Self::new_with_keys(0, 0)
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}
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/// Creates a `SipHasher13` that is keyed off the provided keys.
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fn new_with_keys(key0: u64, key1: u64) -> Self {
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let mut state = SipHasher13 {
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k0: key0,
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k1: key1,
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length: 0,
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state: State {
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v0: 0,
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v1: 0,
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v2: 0,
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v3: 0,
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},
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tail: 0,
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ntail: 0,
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};
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state.reset();
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state
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}
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fn reset(&mut self) {
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self.length = 0;
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self.state.v0 = self.k0 ^ 0x736f6d6570736575;
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self.state.v1 = self.k1 ^ 0x646f72616e646f6d;
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self.state.v2 = self.k0 ^ 0x6c7967656e657261;
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self.state.v3 = self.k1 ^ 0x7465646279746573;
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self.ntail = 0;
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}
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}
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impl Hasher for SipHasher13 {
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// Note: no integer hashing methods (`write_u*`, `write_i*`) are defined
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// for this type. We could add them, copy the `short_write` implementation
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// in librustc_data_structures/sip128.rs, and add `write_u*`/`write_i*`
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// methods to `SipHasher`, `SipHasher13`, and `DefaultHasher`. This would
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// greatly speed up integer hashing by those hashers, at the cost of
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// slightly slowing down compile speeds on some benchmarks. See #69152 for
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// details.
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fn write(&mut self, msg: &[u8]) {
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let length = msg.len();
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self.length += length;
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let mut needed = 0;
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if self.ntail != 0 {
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needed = 8 - self.ntail;
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// SAFETY: `cmp::min(length, needed)` is guaranteed to not be over `length`
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self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << (8 * self.ntail);
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if length < needed {
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self.ntail += length;
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return;
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} else {
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self.state.v3 ^= self.tail;
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Sip13Rounds::c_rounds(&mut self.state);
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self.state.v0 ^= self.tail;
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self.ntail = 0;
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}
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}
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// Buffered tail is now flushed, process new input.
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let len = length - needed;
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let left = len & 0x7; // len % 8
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let mut i = needed;
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while i < len - left {
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// SAFETY: because `len - left` is the biggest multiple of 8 under
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// `len`, and because `i` starts at `needed` where `len` is `length - needed`,
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// `i + 8` is guaranteed to be less than or equal to `length`.
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let mi = unsafe { load_int_le!(msg, i, u64) };
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self.state.v3 ^= mi;
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Sip13Rounds::c_rounds(&mut self.state);
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self.state.v0 ^= mi;
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i += 8;
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}
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// SAFETY: `i` is now `needed + len.div_euclid(8) * 8`,
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// so `i + left` = `needed + len` = `length`, which is by
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// definition equal to `msg.len()`.
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self.tail = unsafe { u8to64_le(msg, i, left) };
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self.ntail = left;
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}
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fn finish(&self) -> u64 {
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let mut state = self.state;
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let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;
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state.v3 ^= b;
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Sip13Rounds::c_rounds(&mut state);
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state.v0 ^= b;
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state.v2 ^= 0xff;
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Sip13Rounds::d_rounds(&mut state);
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state.v0 ^ state.v1 ^ state.v2 ^ state.v3
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}
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}
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struct Sip13Rounds;
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impl Sip13Rounds {
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fn c_rounds(state: &mut State) {
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compress!(state);
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}
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fn d_rounds(state: &mut State) {
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compress!(state);
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compress!(state);
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compress!(state);
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}
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}
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