zstd: Import xxhash v2.2.0 (#708)

Unsafe parts omitted, noasm build tag added back in.

writeBlocks argument renamed s to please go vet.

zstd/internal/xxhash/README.md

@@ -2,12 +2,7 @@
 
 VENDORED: Go to [github.com/cespare/xxhash](https://github.com/cespare/xxhash) for original package.
 
-
-[![GoDoc](https://godoc.org/github.com/cespare/xxhash?status.svg)](https://godoc.org/github.com/cespare/xxhash)
-[![Build Status](https://travis-ci.org/cespare/xxhash.svg?branch=master)](https://travis-ci.org/cespare/xxhash)
-
-xxhash is a Go implementation of the 64-bit
-[xxHash](http://cyan4973.github.io/xxHash/) algorithm, XXH64. This is a
+xxhash is a Go implementation of the 64-bit [xxHash] algorithm, XXH64. This is a
 high-quality hashing algorithm that is much faster than anything in the Go
 standard library.
 
@@ -28,31 +23,49 @@ func (*Digest) WriteString(string) (int, error)
 func (*Digest) Sum64() uint64
 ```
 
-This implementation provides a fast pure-Go implementation and an even faster
-assembly implementation for amd64.
+The package is written with optimized pure Go and also contains even faster
+assembly implementations for amd64 and arm64. If desired, the `purego` build tag
+opts into using the Go code even on those architectures.
+
+[xxHash]: http://cyan4973.github.io/xxHash/
+
+## Compatibility
+
+This package is in a module and the latest code is in version 2 of the module.
+You need a version of Go with at least "minimal module compatibility" to use
+github.com/cespare/xxhash/v2:
+
+* 1.9.7+ for Go 1.9
+* 1.10.3+ for Go 1.10
+* Go 1.11 or later
+
+I recommend using the latest release of Go.
 
 ## Benchmarks
 
 Here are some quick benchmarks comparing the pure-Go and assembly
 implementations of Sum64.
 
-| input size | purego | asm |
-| --- | --- | --- |
-| 5 B   |  979.66 MB/s |  1291.17 MB/s  |
-| 100 B | 7475.26 MB/s | 7973.40 MB/s  |
-| 4 KB  | 17573.46 MB/s | 17602.65 MB/s |
-| 10 MB | 17131.46 MB/s | 17142.16 MB/s |
+| input size | purego    | asm       |
+| ---------- | --------- | --------- |
+| 4 B        |  1.3 GB/s |  1.2 GB/s |
+| 16 B       |  2.9 GB/s |  3.5 GB/s |
+| 100 B      |  6.9 GB/s |  8.1 GB/s |
+| 4 KB       | 11.7 GB/s | 16.7 GB/s |
+| 10 MB      | 12.0 GB/s | 17.3 GB/s |
 
-These numbers were generated on Ubuntu 18.04 with an Intel i7-8700K CPU using
-the following commands under Go 1.11.2:
+These numbers were generated on Ubuntu 20.04 with an Intel Xeon Platinum 8252C
+CPU using the following commands under Go 1.19.2:
 
 ```
-$ go test -tags purego -benchtime 10s -bench '/xxhash,direct,bytes'
-$ go test -benchtime 10s -bench '/xxhash,direct,bytes'
+benchstat <(go test -tags purego -benchtime 500ms -count 15 -bench 'Sum64$')
+benchstat <(go test -benchtime 500ms -count 15 -bench 'Sum64$')
 ```
 
 ## Projects using this package
 
 - [InfluxDB](https://github.com/influxdata/influxdb)
 - [Prometheus](https://github.com/prometheus/prometheus)
+- [VictoriaMetrics](https://github.com/VictoriaMetrics/VictoriaMetrics)
 - [FreeCache](https://github.com/coocood/freecache)
+- [FastCache](https://github.com/VictoriaMetrics/fastcache)

zstd/internal/xxhash/xxhash.go

@@ -18,19 +18,11 @@ const (
 	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
-)
+// Store the primes in an array as well.
+//
+// The consts are used when possible in Go code to avoid MOVs but we need a
+// contiguous array of the assembly code.
+var primes = [...]uint64{prime1, prime2, prime3, prime4, prime5}
 
 // Digest implements hash.Hash64.
 type Digest struct {
@@ -52,10 +44,10 @@ func New() *Digest {
 
 // Reset clears the Digest's state so that it can be reused.
 func (d *Digest) Reset() {
-	d.v1 = prime1v + prime2
+	d.v1 = primes[0] + prime2
 	d.v2 = prime2
 	d.v3 = 0
-	d.v4 = -prime1v
+	d.v4 = -primes[0]
 	d.total = 0
 	d.n = 0
 }
@@ -71,21 +63,23 @@ func (d *Digest) Write(b []byte) (n int, err error) {
 	n = len(b)
 	d.total += uint64(n)
 
+	memleft := d.mem[d.n&(len(d.mem)-1):]
+
 	if d.n+n < 32 {
 		// This new data doesn't even fill the current block.
-		copy(d.mem[d.n:], b)
+		copy(memleft, b)
 		d.n += n
 		return
 	}
 
 	if d.n > 0 {
 		// Finish off the partial block.
-		copy(d.mem[d.n:], b)
+		c := copy(memleft, b)
 		d.v1 = round(d.v1, u64(d.mem[0:8]))
 		d.v2 = round(d.v2, u64(d.mem[8:16]))
 		d.v3 = round(d.v3, u64(d.mem[16:24]))
 		d.v4 = round(d.v4, u64(d.mem[24:32]))
-		b = b[32-d.n:]
+		b = b[c:]
 		d.n = 0
 	}
 
@@ -135,21 +129,20 @@ func (d *Digest) Sum64() uint64 {
 
 	h += d.total
 
-	i, end := 0, d.n
-	for ; i+8 <= end; i += 8 {
-		k1 := round(0, u64(d.mem[i:i+8]))
+	b := d.mem[:d.n&(len(d.mem)-1)]
+	for ; len(b) >= 8; b = b[8:] {
+		k1 := round(0, u64(b[:8]))
 		h ^= k1
 		h = rol27(h)*prime1 + prime4
 	}
-	if i+4 <= end {
-		h ^= uint64(u32(d.mem[i:i+4])) * prime1
+	if len(b) >= 4 {
+		h ^= uint64(u32(b[:4])) * prime1
 		h = rol23(h)*prime2 + prime3
-		i += 4
+		b = b[4:]
 	}
-	for i < end {
-		h ^= uint64(d.mem[i]) * prime5
+	for ; len(b) > 0; b = b[1:] {
+		h ^= uint64(b[0]) * prime5
 		h = rol11(h) * prime1
-		i++
 	}
 
 	h ^= h >> 33