prometheus/vendor/github.com/cespare/xxhash/xxhash.go

181 lines
3.9 KiB
Go
Raw Normal View History

2017-02-07 03:42:02 -08:00
// Package xxhash implements the 64-bit variant of xxHash (XXH64) as described
// at http://cyan4973.github.io/xxHash/.
package xxhash
import (
"encoding/binary"
"hash"
)
const (
prime1 uint64 = 11400714785074694791
prime2 uint64 = 14029467366897019727
prime3 uint64 = 1609587929392839161
prime4 uint64 = 9650029242287828579
prime5 uint64 = 2870177450012600261
)
// NOTE(caleb): I'm using both consts and vars of the primes. Using consts where
// possible in the Go code is worth a small (but measurable) performance boost
// by avoiding some MOVQs. Vars are needed for the asm and also are useful for
// convenience in the Go code in a few places where we need to intentionally
// avoid constant arithmetic (e.g., v1 := prime1 + prime2 fails because the
// result overflows a uint64).
var (
prime1v = prime1
prime2v = prime2
prime3v = prime3
prime4v = prime4
prime5v = prime5
)
type xxh struct {
v1 uint64
v2 uint64
v3 uint64
v4 uint64
total int
mem [32]byte
n int // how much of mem is used
}
// New creates a new hash.Hash64 that implements the 64-bit xxHash algorithm.
func New() hash.Hash64 {
var x xxh
x.Reset()
return &x
}
func (x *xxh) Reset() {
x.n = 0
x.total = 0
x.v1 = prime1v + prime2
x.v2 = prime2
x.v3 = 0
x.v4 = -prime1v
}
func (x *xxh) Size() int { return 8 }
func (x *xxh) BlockSize() int { return 32 }
// Write adds more data to x. It always returns len(b), nil.
func (x *xxh) Write(b []byte) (n int, err error) {
n = len(b)
x.total += len(b)
if x.n+len(b) < 32 {
// This new data doesn't even fill the current block.
copy(x.mem[x.n:], b)
x.n += len(b)
return
}
if x.n > 0 {
// Finish off the partial block.
copy(x.mem[x.n:], b)
x.v1 = round(x.v1, u64(x.mem[0:8]))
x.v2 = round(x.v2, u64(x.mem[8:16]))
x.v3 = round(x.v3, u64(x.mem[16:24]))
x.v4 = round(x.v4, u64(x.mem[24:32]))
b = b[32-x.n:]
x.n = 0
}
if len(b) >= 32 {
// One or more full blocks left.
b = writeBlocks(x, b)
}
// Store any remaining partial block.
copy(x.mem[:], b)
x.n = len(b)
return
}
func (x *xxh) Sum(b []byte) []byte {
s := x.Sum64()
return append(
b,
byte(s>>56),
byte(s>>48),
byte(s>>40),
byte(s>>32),
byte(s>>24),
byte(s>>16),
byte(s>>8),
byte(s),
)
}
func (x *xxh) Sum64() uint64 {
var h uint64
if x.total >= 32 {
v1, v2, v3, v4 := x.v1, x.v2, x.v3, x.v4
h = rol1(v1) + rol7(v2) + rol12(v3) + rol18(v4)
h = mergeRound(h, v1)
h = mergeRound(h, v2)
h = mergeRound(h, v3)
h = mergeRound(h, v4)
} else {
h = x.v3 + prime5
}
h += uint64(x.total)
i, end := 0, x.n
for ; i+8 <= end; i += 8 {
k1 := round(0, u64(x.mem[i:i+8]))
h ^= k1
h = rol27(h)*prime1 + prime4
}
if i+4 <= end {
h ^= uint64(u32(x.mem[i:i+4])) * prime1
h = rol23(h)*prime2 + prime3
i += 4
}
for i < end {
h ^= uint64(x.mem[i]) * prime5
h = rol11(h) * prime1
i++
}
h ^= h >> 33
h *= prime2
h ^= h >> 29
h *= prime3
h ^= h >> 32
return h
}
func u64(b []byte) uint64 { return binary.LittleEndian.Uint64(b) }
func u32(b []byte) uint32 { return binary.LittleEndian.Uint32(b) }
func round(acc, input uint64) uint64 {
acc += input * prime2
acc = rol31(acc)
acc *= prime1
return acc
}
func mergeRound(acc, val uint64) uint64 {
val = round(0, val)
acc ^= val
acc = acc*prime1 + prime4
return acc
}
// It's important for performance to get the rotates to actually compile to
// ROLQs. gc will do this for us but only if rotate amount is a constant.
func rol1(x uint64) uint64 { return (x << 1) | (x >> (64 - 1)) }
func rol7(x uint64) uint64 { return (x << 7) | (x >> (64 - 7)) }
func rol11(x uint64) uint64 { return (x << 11) | (x >> (64 - 11)) }
func rol12(x uint64) uint64 { return (x << 12) | (x >> (64 - 12)) }
func rol18(x uint64) uint64 { return (x << 18) | (x >> (64 - 18)) }
func rol23(x uint64) uint64 { return (x << 23) | (x >> (64 - 23)) }
func rol27(x uint64) uint64 { return (x << 27) | (x >> (64 - 27)) }
func rol31(x uint64) uint64 { return (x << 31) | (x >> (64 - 31)) }