diff options
| author | Keith Randall <khr@golang.org> | 2024-04-18 14:05:55 -0700 |
|---|---|---|
| committer | Keith Randall <khr@google.com> | 2024-04-19 17:39:28 +0000 |
| commit | 35c619398b976bf90fb8c813653cf48ce732b032 (patch) | |
| tree | ecdc46820eacb5b6d8b25de14870c37168844c23 | |
| parent | c260de24b688d72206f1224e298181c8363fc33d (diff) | |
| download | go-35c619398b976bf90fb8c813653cf48ce732b032.tar.gz go-35c619398b976bf90fb8c813653cf48ce732b032.zip | |
runtime: for fallback hash, get rid of constant xors
There's no need for these. If hashkey[i] is uniform over [0,1<<64), then
hashkey[0]^C has exactly the same distribution, for any constant C.
Change-Id: I4e10c27eff15e4b7a45139654ac41f410b1b12fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/580218
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
| -rw-r--r-- | src/runtime/hash64.go | 20 |
1 files changed, 8 insertions, 12 deletions
diff --git a/src/runtime/hash64.go b/src/runtime/hash64.go index bd16b7cd96..05cdb81113 100644 --- a/src/runtime/hash64.go +++ b/src/runtime/hash64.go @@ -15,16 +15,12 @@ import ( ) const ( - m1 = 0xa0761d6478bd642f - m2 = 0xe7037ed1a0b428db - m3 = 0x8ebc6af09c88c6e3 - m4 = 0x589965cc75374cc3 m5 = 0x1d8e4e27c47d124f ) func memhashFallback(p unsafe.Pointer, seed, s uintptr) uintptr { var a, b uintptr - seed ^= hashkey[0] ^ m1 + seed ^= hashkey[0] switch { case s == 0: return seed @@ -50,32 +46,32 @@ func memhashFallback(p unsafe.Pointer, seed, s uintptr) uintptr { seed1 := seed seed2 := seed for ; l > 48; l -= 48 { - seed = mix(r8(p)^hashkey[1]^m2, r8(add(p, 8))^seed) - seed1 = mix(r8(add(p, 16))^hashkey[2]^m3, r8(add(p, 24))^seed1) - seed2 = mix(r8(add(p, 32))^hashkey[3]^m4, r8(add(p, 40))^seed2) + seed = mix(r8(p)^hashkey[1], r8(add(p, 8))^seed) + seed1 = mix(r8(add(p, 16))^hashkey[2], r8(add(p, 24))^seed1) + seed2 = mix(r8(add(p, 32))^hashkey[3], r8(add(p, 40))^seed2) p = add(p, 48) } seed ^= seed1 ^ seed2 } for ; l > 16; l -= 16 { - seed = mix(r8(p)^hashkey[1]^m2, r8(add(p, 8))^seed) + seed = mix(r8(p)^hashkey[1], r8(add(p, 8))^seed) p = add(p, 16) } a = r8(add(p, l-16)) b = r8(add(p, l-8)) } - return mix(m5^s, mix(a^hashkey[1]^m2, b^seed)) + return mix(m5^s, mix(a^hashkey[1], b^seed)) } func memhash32Fallback(p unsafe.Pointer, seed uintptr) uintptr { a := r4(p) - return mix(m5^4, mix(a^hashkey[1]^m2, a^seed^hashkey[0]^m1)) + return mix(m5^4, mix(a^hashkey[1], a^seed^hashkey[0])) } func memhash64Fallback(p unsafe.Pointer, seed uintptr) uintptr { a := r8(p) - return mix(m5^8, mix(a^hashkey[1]^m2, a^seed^hashkey[0]^m1)) + return mix(m5^8, mix(a^hashkey[1], a^seed^hashkey[0])) } func mix(a, b uintptr) uintptr { |