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package fnv1a
const (
// FNV-1a
offset64 = uint64(14695981039346656037)
prime64 = uint64(1099511628211)
// Init64 is what 64 bits hash values should be initialized with.
Init64 = offset64
)
// HashString64 returns the hash of s.
func HashString64(s string) uint64 {
return AddString64(Init64, s)
}
// HashBytes64 returns the hash of u.
func HashBytes64(b []byte) uint64 {
return AddBytes64(Init64, b)
}
// HashUint64 returns the hash of u.
func HashUint64(u uint64) uint64 {
return AddUint64(Init64, u)
}
// AddString64 adds the hash of s to the precomputed hash value h.
func AddString64(h uint64, s string) uint64 {
/*
This is an unrolled version of this algorithm:
for _, c := range s {
h = (h ^ uint64(c)) * prime64
}
It seems to be ~1.5x faster than the simple loop in BenchmarkHash64:
- BenchmarkHash64/hash_function-4 30000000 56.1 ns/op 642.15 MB/s 0 B/op 0 allocs/op
- BenchmarkHash64/hash_function-4 50000000 38.6 ns/op 932.35 MB/s 0 B/op 0 allocs/op
*/
for len(s) >= 8 {
h = (h ^ uint64(s[0])) * prime64
h = (h ^ uint64(s[1])) * prime64
h = (h ^ uint64(s[2])) * prime64
h = (h ^ uint64(s[3])) * prime64
h = (h ^ uint64(s[4])) * prime64
h = (h ^ uint64(s[5])) * prime64
h = (h ^ uint64(s[6])) * prime64
h = (h ^ uint64(s[7])) * prime64
s = s[8:]
}
if len(s) >= 4 {
h = (h ^ uint64(s[0])) * prime64
h = (h ^ uint64(s[1])) * prime64
h = (h ^ uint64(s[2])) * prime64
h = (h ^ uint64(s[3])) * prime64
s = s[4:]
}
if len(s) >= 2 {
h = (h ^ uint64(s[0])) * prime64
h = (h ^ uint64(s[1])) * prime64
s = s[2:]
}
if len(s) > 0 {
h = (h ^ uint64(s[0])) * prime64
}
return h
}
// AddBytes64 adds the hash of b to the precomputed hash value h.
func AddBytes64(h uint64, b []byte) uint64 {
for len(b) >= 8 {
h = (h ^ uint64(b[0])) * prime64
h = (h ^ uint64(b[1])) * prime64
h = (h ^ uint64(b[2])) * prime64
h = (h ^ uint64(b[3])) * prime64
h = (h ^ uint64(b[4])) * prime64
h = (h ^ uint64(b[5])) * prime64
h = (h ^ uint64(b[6])) * prime64
h = (h ^ uint64(b[7])) * prime64
b = b[8:]
}
if len(b) >= 4 {
h = (h ^ uint64(b[0])) * prime64
h = (h ^ uint64(b[1])) * prime64
h = (h ^ uint64(b[2])) * prime64
h = (h ^ uint64(b[3])) * prime64
b = b[4:]
}
if len(b) >= 2 {
h = (h ^ uint64(b[0])) * prime64
h = (h ^ uint64(b[1])) * prime64
b = b[2:]
}
if len(b) > 0 {
h = (h ^ uint64(b[0])) * prime64
}
return h
}
// AddUint64 adds the hash value of the 8 bytes of u to h.
func AddUint64(h uint64, u uint64) uint64 {
h = (h ^ ((u >> 56) & 0xFF)) * prime64
h = (h ^ ((u >> 48) & 0xFF)) * prime64
h = (h ^ ((u >> 40) & 0xFF)) * prime64
h = (h ^ ((u >> 32) & 0xFF)) * prime64
h = (h ^ ((u >> 24) & 0xFF)) * prime64
h = (h ^ ((u >> 16) & 0xFF)) * prime64
h = (h ^ ((u >> 8) & 0xFF)) * prime64
h = (h ^ ((u >> 0) & 0xFF)) * prime64
return h
}
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