n%8 is not what you want. n - n%8 is what you want, best expressed as n &^0x7
On Mon, Mar 18, 2019 at 7:36 PM zhou yu <yuzhou....@gmail.com> wrote: > *Why the XOR between*(*[]uintptr)(unsafe.Pointer(&dst)) is fast then > []byte?* > > I find a fast xor lib https://github.com/templexxx/xor, and write the > benchmark below, > > the result show that BenchmarkFastXORWords is 5x faster than BenchmarkS > afeXORBytes on my computer > > I can't figure out why? Anyone can help me. THX > > package main > > import ( > "math/rand" > "testing" > "unsafe" > ) > > const wordSize = int(unsafe.Sizeof(uintptr(0))) > > var e = make([]byte, 160) > var f = make([]byte, 160) > var g = make([]byte, 160) > > func init() { > for i := 0; i < 160; i++ { > rand.Seed(22) > e[i] = byte(rand.Intn(256)) > f[i] = byte(rand.Intn(256)) > } > } > > func BenchmarkSafeXORBytes(b *testing.B) { > for i := 0; i < b.N; i++ { > safeXORBytes(g, e, f) > } > } > > func BenchmarkFastXORWords(b *testing.B) { > for i := 0; i < b.N; i++ { > fastXORWords(g, e, f) > } > } > > func safeXORBytes(dst, a, b []byte) { > n := len(a) > ex := n % 8 > for i := 0; i < ex; i++ { > dst[i] = a[i] ^ b[i] > } > > for i := ex; i < n; i += 8 { > _dst := dst[i : i+8] > _a := a[i : i+8] > _b := b[i : i+8] > _dst[0] = _a[0] ^ _b[0] > _dst[1] = _a[1] ^ _b[1] > _dst[2] = _a[2] ^ _b[2] > _dst[3] = _a[3] ^ _b[3] > > _dst[4] = _a[4] ^ _b[4] > _dst[5] = _a[5] ^ _b[5] > _dst[6] = _a[6] ^ _b[6] > _dst[7] = _a[7] ^ _b[7] > } > } > > func fastXORWords(dst, a, b []byte) { > dw := *(*[]uintptr)(unsafe.Pointer(&dst)) > aw := *(*[]uintptr)(unsafe.Pointer(&a)) > bw := *(*[]uintptr)(unsafe.Pointer(&b)) > n := len(b) / wordSize > ex := n % 8 > for i := 0; i < ex; i++ { > dw[i] = aw[i] ^ bw[i] > } > > for i := ex; i < n; i += 8 { > _dw := dw[i : i+8] > _aw := aw[i : i+8] > _bw := bw[i : i+8] > _dw[0] = _aw[0] ^ _bw[0] > _dw[1] = _aw[1] ^ _bw[1] > _dw[2] = _aw[2] ^ _bw[2] > _dw[3] = _aw[3] ^ _bw[3] > _dw[4] = _aw[4] ^ _bw[4] > _dw[5] = _aw[5] ^ _bw[5] > _dw[6] = _aw[6] ^ _bw[6] > _dw[7] = _aw[7] ^ _bw[7] > } > } > > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- *Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>* -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
