88 lines
2.2 KiB
Go
88 lines
2.2 KiB
Go
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// Package fnv128a implements FNV-1 and FNV-1a, non-cryptographic hash functions
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// created by Glenn Fowler, Landon Curt Noll, and Phong Vo.
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// See https://en.wikipedia.org/wiki/Fowler-Noll-Vo_hash_function.
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//
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// Write() algorithm taken and modified from github.com/romain-jacotin/quic
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package fnv128a
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import "hash"
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// Hash128 is the common interface implemented by all 128-bit hash functions.
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type Hash128 interface {
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hash.Hash
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Sum128() (uint64, uint64)
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}
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type sum128a struct {
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v0, v1, v2, v3 uint64
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}
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var _ Hash128 = &sum128a{}
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// New1 returns a new 128-bit FNV-1a hash.Hash.
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func New() Hash128 {
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s := &sum128a{}
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s.Reset()
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return s
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}
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func (s *sum128a) Reset() {
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s.v0 = 0x6295C58D
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s.v1 = 0x62B82175
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s.v2 = 0x07BB0142
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s.v3 = 0x6C62272E
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}
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func (s *sum128a) Sum128() (uint64, uint64) {
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return s.v3<<32 | s.v2, s.v1<<32 | s.v0
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}
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func (s *sum128a) Write(data []byte) (int, error) {
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var t0, t1, t2, t3 uint64
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const fnv128PrimeLow = 0x0000013B
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const fnv128PrimeShift = 24
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for _, v := range data {
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// xor the bottom with the current octet
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s.v0 ^= uint64(v)
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// multiply by the 128 bit FNV magic prime mod 2^128
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// fnv_prime = 309485009821345068724781371 (decimal)
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// = 0x0000000001000000000000000000013B (hexadecimal)
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// = 0x00000000 0x01000000 0x00000000 0x0000013B (in 4*32 words)
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// = 0x0 1<<fnv128PrimeShift 0x0 fnv128PrimeLow
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//
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// fnv128PrimeLow = 0x0000013B
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// fnv128PrimeShift = 24
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// multiply by the lowest order digit base 2^32 and by the other non-zero digit
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t0 = s.v0 * fnv128PrimeLow
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t1 = s.v1 * fnv128PrimeLow
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t2 = s.v2*fnv128PrimeLow + s.v0<<fnv128PrimeShift
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t3 = s.v3*fnv128PrimeLow + s.v1<<fnv128PrimeShift
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// propagate carries
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t1 += (t0 >> 32)
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t2 += (t1 >> 32)
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t3 += (t2 >> 32)
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s.v0 = t0 & 0xffffffff
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s.v1 = t1 & 0xffffffff
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s.v2 = t2 & 0xffffffff
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s.v3 = t3 // & 0xffffffff
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// Doing a s.v3 &= 0xffffffff is not really needed since it simply
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// removes multiples of 2^128. We can discard these excess bits
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// outside of the loop when writing the hash in Little Endian.
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}
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return len(data), nil
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}
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func (s *sum128a) Size() int { return 16 }
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func (s *sum128a) BlockSize() int { return 1 }
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func (s *sum128a) Sum(in []byte) []byte {
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panic("FNV: not supported")
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}
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