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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Hashing algorithm inspired by
// xxhash: https://code.google.com/p/xxhash/
// cityhash: https://code.google.com/p/cityhash/
// +build 386 arm
package runtime
import "unsafe"
const (
// Constants for multiplication: four random odd 32-bit numbers.
m1 = 3168982561
m2 = 3339683297
m3 = 832293441
m4 = 2336365089
)
func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
if GOARCH == "386" && GOOS != "nacl" && useAeshash {
return aeshash(p, seed, s)
}
h := uint32(seed + s*hashkey[0])
tail:
switch {
case s == 0:
case s < 4:
h ^= uint32(*(*byte)(p))
h ^= uint32(*(*byte)(add(p, s>>1))) << 8
h ^= uint32(*(*byte)(add(p, s-1))) << 16
h = rotl_15(h*m1) * m2
case s == 4:
h ^= readUnaligned32(p)
h = rotl_15(h*m1) * m2
case s <= 8:
h ^= readUnaligned32(p)
h = rotl_15(h*m1) * m2
h ^= readUnaligned32(add(p, s-4))
h = rotl_15(h*m1) * m2
case s <= 16:
h ^= readUnaligned32(p)
h = rotl_15(h*m1) * m2
h ^= readUnaligned32(add(p, 4))
h = rotl_15(h*m1) * m2
h ^= readUnaligned32(add(p, s-8))
h = rotl_15(h*m1) * m2
h ^= readUnaligned32(add(p, s-4))
h = rotl_15(h*m1) * m2
default:
v1 := h
v2 := uint32(hashkey[1])
v3 := uint32(hashkey[2])
v4 := uint32(hashkey[3])
for s >= 16 {
v1 ^= readUnaligned32(p)
v1 = rotl_15(v1*m1) * m2
p = add(p, 4)
v2 ^= readUnaligned32(p)
v2 = rotl_15(v2*m2) * m3
p = add(p, 4)
v3 ^= readUnaligned32(p)
v3 = rotl_15(v3*m3) * m4
p = add(p, 4)
v4 ^= readUnaligned32(p)
v4 = rotl_15(v4*m4) * m1
p = add(p, 4)
s -= 16
}
h = v1 ^ v2 ^ v3 ^ v4
goto tail
}
h ^= h >> 17
h *= m3
h ^= h >> 13
h *= m4
h ^= h >> 16
return uintptr(h)
}
// Note: in order to get the compiler to issue rotl instructions, we
// need to constant fold the shift amount by hand.
// TODO: convince the compiler to issue rotl instructions after inlining.
func rotl_15(x uint32) uint32 {
return (x << 15) | (x >> (32 - 15))
}
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