thanks for you review. i just want to figure out why the fastXOR is fast then the safe one, so I cut out the source, maybe this cause the demo is not rebust like it in the repo, and if did have some mistake maybe you can pr the https://github.com/templexxx/xor.
在 2019年3月19日星期二 UTC+8下午3:32:52，Michael Jones写道： > > Ok, at my computer now so time for a longer answer. > > What you want is this: > https://play.golang.org/p/QirBtj523Wu > > Now, what's wrong with the code you sent? Quite a few things actually. > Maybe you should start with the code shared above and then work through > what it is doing, then compare that with the original alternatives. > > Michael > > On Mon, Mar 18, 2019 at 9:58 PM Michael Jones <[email protected] > <javascript:>> wrote: > >> 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 <[email protected] <javascript:>> >> 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 [email protected] <javascript:>. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> -- >> >> *Michael T. [email protected] <javascript:>* >> > > > -- > > *Michael T. [email protected] <javascript:>* > -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
