75 lines
1.3 KiB
Go
75 lines
1.3 KiB
Go
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package halfsiphash
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import "encoding/binary"
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func rotl(x uint32, b uint) uint32 {
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return (x << b) | (x >> (32 - b))
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}
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func sipround(v0, v1, v2, v3 *uint32) {
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*v0 += *v1
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*v1 = rotl(*v1, 5)
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*v1 ^= *v0
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*v0 = rotl(*v0, 16)
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*v2 += *v3
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*v3 = rotl(*v3, 8)
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*v3 ^= *v2
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*v0 += *v3
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*v3 = rotl(*v3, 7)
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*v3 ^= *v0
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*v2 += *v1
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*v1 = rotl(*v1, 13)
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*v1 ^= *v2
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*v2 = rotl(*v2, 16)
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}
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// Sum32 computes HalfSipHash-2-4 with an 8-byte key and returns a 4-byte hash.
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func Sum32(data []byte, key [8]byte) uint32 {
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k0 := binary.LittleEndian.Uint32(key[0:4])
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k1 := binary.LittleEndian.Uint32(key[4:8])
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v0 := uint32(0) ^ k0
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v1 := uint32(0) ^ k1
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v2 := uint32(0x6c796765) ^ k0
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v3 := uint32(0x74656462) ^ k1
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// Process full 4-byte blocks.
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nblocks := len(data) / 4
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for i := 0; i < nblocks; i++ {
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m := binary.LittleEndian.Uint32(data[i*4:])
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v3 ^= m
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for j := 0; j < 2; j++ {
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sipround(&v0, &v1, &v2, &v3)
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}
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v0 ^= m
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}
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// Process remaining bytes.
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b := uint32(len(data)) << 24
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tail := data[nblocks*4:]
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switch len(tail) {
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case 3:
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b |= uint32(tail[2]) << 16
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fallthrough
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case 2:
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b |= uint32(tail[1]) << 8
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fallthrough
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case 1:
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b |= uint32(tail[0])
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}
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v3 ^= b
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for i := 0; i < 2; i++ {
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sipround(&v0, &v1, &v2, &v3)
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}
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v0 ^= b
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v2 ^= 0xff
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for i := 0; i < 4; i++ {
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sipround(&v0, &v1, &v2, &v3)
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}
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return v1 ^ v3
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}
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