/
hash64.go
67 lines (61 loc) · 1.37 KB
/
hash64.go
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//go:build amd64 || arm64 || mips64 || mips64le || ppc64 || ppc64le || riscv64 || s390x || wasm
package internal
import (
"math/bits"
"unsafe"
)
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 ^= m1
switch {
case s == 0:
return seed
case s < 4:
a = uintptr(*(*byte)(p))
a |= uintptr(*(*byte)(unsafe.Add(p, s>>1))) << 8
a |= uintptr(*(*byte)(unsafe.Add(p, s-1))) << 16
case s == 4:
a = r4(p)
b = a
case s < 8:
a = r4(p)
b = r4(unsafe.Add(p, s-4))
case s == 8:
a = r8(p)
b = a
case s <= 16:
a = r8(p)
b = r8(unsafe.Add(p, s-8))
default:
l := s
if l > 48 {
seed1 := seed
seed2 := seed
for ; l > 48; l -= 48 {
seed = mix(r8(p)^m2, r8(unsafe.Add(p, 8))^seed)
seed1 = mix(r8(unsafe.Add(p, 16))^m3, r8(unsafe.Add(p, 24))^seed1)
seed2 = mix(r8(unsafe.Add(p, 32))^m4, r8(unsafe.Add(p, 40))^seed2)
p = unsafe.Add(p, 48)
}
seed ^= seed1 ^ seed2
}
for ; l > 16; l -= 16 {
seed = mix(r8(p)^m2, r8(unsafe.Add(p, 8))^seed)
p = unsafe.Add(p, 16)
}
a = r8(unsafe.Add(p, l-16))
b = r8(unsafe.Add(p, l-8))
}
return mix(m5^s, mix(a^m2, b^seed))
}
func mix(a, b uintptr) uintptr {
hi, lo := bits.Mul64(uint64(a), uint64(b))
return uintptr(hi ^ lo)
}