1// Package xxhash implements the 64-bit variant of xxHash (XXH64) as described
2// at http://cyan4973.github.io/xxHash/.
3package xxhash
4
5import (
6	"encoding/binary"
7	"hash"
8)
9
10const (
11	prime1 uint64 = 11400714785074694791
12	prime2 uint64 = 14029467366897019727
13	prime3 uint64 = 1609587929392839161
14	prime4 uint64 = 9650029242287828579
15	prime5 uint64 = 2870177450012600261
16)
17
18// NOTE(caleb): I'm using both consts and vars of the primes. Using consts where
19// possible in the Go code is worth a small (but measurable) performance boost
20// by avoiding some MOVQs. Vars are needed for the asm and also are useful for
21// convenience in the Go code in a few places where we need to intentionally
22// avoid constant arithmetic (e.g., v1 := prime1 + prime2 fails because the
23// result overflows a uint64).
24var (
25	prime1v = prime1
26	prime2v = prime2
27	prime3v = prime3
28	prime4v = prime4
29	prime5v = prime5
30)
31
32type xxh struct {
33	v1    uint64
34	v2    uint64
35	v3    uint64
36	v4    uint64
37	total int
38	mem   [32]byte
39	n     int // how much of mem is used
40}
41
42// New creates a new hash.Hash64 that implements the 64-bit xxHash algorithm.
43func New() hash.Hash64 {
44	var x xxh
45	x.Reset()
46	return &x
47}
48
49func (x *xxh) Reset() {
50	x.n = 0
51	x.total = 0
52	x.v1 = prime1v + prime2
53	x.v2 = prime2
54	x.v3 = 0
55	x.v4 = -prime1v
56}
57
58func (x *xxh) Size() int      { return 8 }
59func (x *xxh) BlockSize() int { return 32 }
60
61// Write adds more data to x. It always returns len(b), nil.
62func (x *xxh) Write(b []byte) (n int, err error) {
63	n = len(b)
64	x.total += len(b)
65
66	if x.n+len(b) < 32 {
67		// This new data doesn't even fill the current block.
68		copy(x.mem[x.n:], b)
69		x.n += len(b)
70		return
71	}
72
73	if x.n > 0 {
74		// Finish off the partial block.
75		copy(x.mem[x.n:], b)
76		x.v1 = round(x.v1, u64(x.mem[0:8]))
77		x.v2 = round(x.v2, u64(x.mem[8:16]))
78		x.v3 = round(x.v3, u64(x.mem[16:24]))
79		x.v4 = round(x.v4, u64(x.mem[24:32]))
80		b = b[32-x.n:]
81		x.n = 0
82	}
83
84	if len(b) >= 32 {
85		// One or more full blocks left.
86		b = writeBlocks(x, b)
87	}
88
89	// Store any remaining partial block.
90	copy(x.mem[:], b)
91	x.n = len(b)
92
93	return
94}
95
96func (x *xxh) Sum(b []byte) []byte {
97	s := x.Sum64()
98	return append(
99		b,
100		byte(s>>56),
101		byte(s>>48),
102		byte(s>>40),
103		byte(s>>32),
104		byte(s>>24),
105		byte(s>>16),
106		byte(s>>8),
107		byte(s),
108	)
109}
110
111func (x *xxh) Sum64() uint64 {
112	var h uint64
113
114	if x.total >= 32 {
115		v1, v2, v3, v4 := x.v1, x.v2, x.v3, x.v4
116		h = rol1(v1) + rol7(v2) + rol12(v3) + rol18(v4)
117		h = mergeRound(h, v1)
118		h = mergeRound(h, v2)
119		h = mergeRound(h, v3)
120		h = mergeRound(h, v4)
121	} else {
122		h = x.v3 + prime5
123	}
124
125	h += uint64(x.total)
126
127	i, end := 0, x.n
128	for ; i+8 <= end; i += 8 {
129		k1 := round(0, u64(x.mem[i:i+8]))
130		h ^= k1
131		h = rol27(h)*prime1 + prime4
132	}
133	if i+4 <= end {
134		h ^= uint64(u32(x.mem[i:i+4])) * prime1
135		h = rol23(h)*prime2 + prime3
136		i += 4
137	}
138	for i < end {
139		h ^= uint64(x.mem[i]) * prime5
140		h = rol11(h) * prime1
141		i++
142	}
143
144	h ^= h >> 33
145	h *= prime2
146	h ^= h >> 29
147	h *= prime3
148	h ^= h >> 32
149
150	return h
151}
152
153func u64(b []byte) uint64 { return binary.LittleEndian.Uint64(b) }
154func u32(b []byte) uint32 { return binary.LittleEndian.Uint32(b) }
155
156func round(acc, input uint64) uint64 {
157	acc += input * prime2
158	acc = rol31(acc)
159	acc *= prime1
160	return acc
161}
162
163func mergeRound(acc, val uint64) uint64 {
164	val = round(0, val)
165	acc ^= val
166	acc = acc*prime1 + prime4
167	return acc
168}
169