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wyhash: stateless is faster for both iterative hashing and small keys.

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This commit is contained in:
Sahnvour 2019-07-16 20:31:02 +02:00
parent 4b5172d287
commit 3faf5d3857
1 changed files with 20 additions and 32 deletions
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52
std/hash/wyhash.zig
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@ -33,16 +33,11 @@ fn mix1(a: u64, b: u64, seed: u64) u64 {
pub const Wyhash = struct {
seed: u64,
buf: [32]u8,
buf_len: usize,
msg_len: usize,
pub fn init(seed: u64) Wyhash {
return Wyhash{
.seed = seed,
.buf = undefined,
.buf_len = 0,
.msg_len = 0,
};
}
@ -61,34 +56,12 @@ pub const Wyhash = struct {
);
}
pub fn update(self: *Wyhash, b: []const u8) void {
var off: usize = 0;
fn partial(self: *Wyhash, b: []const u8) void {
const rem_key = b;
const rem_len = b.len;
// Partial from previous.
if (self.buf_len != 0 and self.buf_len + b.len > 32) {
off += 32 - self.buf_len;
mem.copy(u8, self.buf[self.buf_len..], b[0..off]);
self.round(self.buf[0..]);
self.buf_len = 0;
}
// Full middle blocks.
while (off + 32 <= b.len) : (off += 32) {
@inlineCall(self.round, b[off .. off + 32]);
}
// Remainder for next pass.
mem.copy(u8, self.buf[self.buf_len..], b[off..]);
self.buf_len += @intCast(u8, b[off..].len);
self.msg_len += b.len;
}
pub fn final(self: *Wyhash) u64 {
const seed = self.seed;
const rem_len = @intCast(u5, self.buf_len);
const rem_key = self.buf[0..self.buf_len];
self.seed = switch (rem_len) {
var seed = self.seed;
seed = switch (@intCast(u5, rem_len)) {
0 => seed,
1 => mix0(read_bytes(1, rem_key), primes[4], seed),
2 => mix0(read_bytes(2, rem_key), primes[4], seed),
@ -122,7 +95,22 @@ pub const Wyhash = struct {
30 => mix0(read_8bytes_swapped(rem_key), read_8bytes_swapped(rem_key[8..]), seed) ^ mix1(read_8bytes_swapped(rem_key[16..]), (read_bytes(4, rem_key[24..]) << 16) | read_bytes(2, rem_key[28..]), seed),
31 => mix0(read_8bytes_swapped(rem_key), read_8bytes_swapped(rem_key[8..]), seed) ^ mix1(read_8bytes_swapped(rem_key[16..]), (read_bytes(4, rem_key[24..]) << 24) | (read_bytes(2, rem_key[28..]) << 8) | read_bytes(1, rem_key[30..]), seed),
};
self.seed = seed;
}
pub fn update(self: *Wyhash, b: []const u8) void {
var off: usize = 0;
// Full middle blocks.
while (off + 32 <= b.len) : (off += 32) {
@inlineCall(self.round, b[off .. off + 32]);
}
self.partial(b[off..]);
self.msg_len += b.len;
}
pub fn final(self: *Wyhash) u64 {
return mum(self.seed ^ self.msg_len, primes[4]);
}