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在Go语言中计算hashCode

gohashcode
3

Java对象有一个hashCode，比加密哈希更便宜。如何在Go中实现这样的hashCode？

1个回答
6
Go编程语言是开源的。你可以查看它的标准库，找到一个快速高效的Go哈希实现。
以下是它们的位置： 它们是未公开的，但如果您需要在应用程序中使用它们，只需将代码复制到您的项目中即可。此外，请注意，如果您的CPU支持它，Go运行时会使用aeshash来利用您的CPU能力。
引用更短的32位版本：
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(seed * hashkey[1])
        v3 := uint32(seed * hashkey[2])
        v4 := uint32(seed * 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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