B计划之大整数的内存复制

无心人

你不知道movdqu很慢么？ 如果那么做，还不如4路展开的双字拷贝 另外，这种情况下，总是双字对齐的 所以可比字节对齐要多些选择

liangbch

具体性能如何，等测试完才知道。 我可能在下周一给出结论，五一休息3天，不准备写代码。

无心人

关键是涉及到两个串 另外，串传送指令在这里不如普通指令

liangbch

我手边有2年前写的代码，在PIV 2.6G 上重新运行，结果如下。 4 copy function speed test,time unit: second,length unint: DWORD address =16X+0 length A_Copy A_Copy_With_SSE2 memcpy A_Copy_R4 16384 0.000013566506 0.000015056064 0.000009504872 0.000015172883 4 copy function speed test,time unit: second,length unint: DWORD address =16X+4 length A_Copy A_Copy_With_SSE2 memcpy A_Copy_R4 16384 0.000025271835 0.000048835081 0.000018014919 0.000015590487 说明： 1.A_Copy 使用"rep movsd" 2.A_Copy_With_SSE2 使用movdqu 和movdqa,可能不是最优化的。 3.A_Copy_R4 使用4路展开的 mov指令,代码如下： mov eax,[esi] mov ebx,[esi+4] mov ecx,[esi+8] mov edx,[esi+12] mov [edi], eax mov [edi+4], ebx mov [edi+8], ecx mov [edi+12],edx add esi,16 add edi,16 结论： 1.当16字节对齐时， memcpy 最快，A_Copy 次之，A_Copy_With_SSE2 和 A_Copy_R4 速度大致相当，慢于memcpy。 2.当16x+4字节对齐时，A_Copy_R4 最快，memcpy 次之，A_Copy 第三，而A_Copy_With_SSE2则比前几个慢上好多。 3.值得注意的是，memcpy性能相当好，超过了SSE2的版本，这验证了我在 http://bbs.emath.ac.cn/thread-273-3-1.html 23# 所言。 题外话，代码大全中谈到关于优化的规则：第一：不要用汇编优化，第二：还是不要用汇编优化。不经测试，一味的使用最先进的指令，极可能使得程序更慢。

无心人

你说的是intel编译器里的memcpy还是标准库？

liangbch

程序是使用VC6.0编译的，未使用intel的编译器。

无心人

标准库似乎就是串操作吧？

无心人

你可以写个程序试一试，可能你先前的观念是错误的。pshufd 绝不会比 movdqa 快。

无心人

复制存在一个问题 块小了用movdqa快， 大了用movntdq快 不知道如何判断

liangbch

原帖由 无心人 于 2008-4-30 14:43 发表 标准库似乎就是串操作吧？

错，标准库的memcpy代码很复杂，使用的并非是串操作，核心部分是一个8路循环展开，采用以下的形式的代码 mov eax,[esi+ecx*4-28] ;U - get dword from source ;V - spare mov [edi+ecx*4-28],eax ;U - put dword into destination 下面贴出vc 6.0 中的 memcpy的源代码： page ,132 title memcpy - Copy source memory bytes to destination ;*** ;memcpy.asm - contains memcpy and memmove routines ; ; Copyright (c) 1986-1997, Microsoft Corporation. All right reserved. ; ; Purpose: ; memcpy() copies a source memory buffer to a destination buffer. ; Overlapping buffers are not treated specially, so propogation may occur. ; memmove() copies a source memory buffer to a destination buffer. ; Overlapping buffers are treated specially, to avoid propogation. ; ;******************************************************************************* .xlist include cruntime.inc .list M_EXIT macro ret ; _cdecl return endm ; M_EXIT CODESEG page ;*** ;memcpy - Copy source buffer to destination buffer ; ; Purpose: ; memcpy() copies a source memory buffer to a destination memory buffer. ; This routine does NOT recognize overlapping buffers, and thus can lead ; to propogation. ; For cases where propogation must be avoided, memmove() must be used. ; ; Algorithm: ; ; void * memcpy(void * dst, void * src, size_t count) ; { ; void * ret = dst; ; ; /* ; * copy from lower addresses to higher addresses ; */ ; while (count--) ; *dst++ = *src++; ; ; return(ret); ; } ; ;memmove - Copy source buffer to destination buffer ; ; Purpose: ; memmove() copies a source memory buffer to a destination memory buffer. ; This routine recognize overlapping buffers to avoid propogation. ; For cases where propogation is not a problem, memcpy() can be used. ; ; Algorithm: ; ; void * memmove(void * dst, void * src, size_t count) ; { ; void * ret = dst; ; ; if (dst <= src || dst >= (src + count)) { ; /* ; * Non-Overlapping Buffers ; * copy from lower addresses to higher addresses ; */ ; while (count--) ; *dst++ = *src++; ; } ; else { ; /* ; * Overlapping Buffers ; * copy from higher addresses to lower addresses ; */ ; dst += count - 1; ; src += count - 1; ; ; while (count--) ; *dst-- = *src--; ; } ; ; return(ret); ; } ; ; ;Entry: ; void *dst = pointer to destination buffer ; const void *src = pointer to source buffer ; size_t count = number of bytes to copy ; ;Exit: ; Returns a pointer to the destination buffer in AX/DX:AX ; ;Uses: ; CX, DX ; ;Exceptions: ;******************************************************************************* ifdef MEM_MOVE _MEM_ equ else ; MEM_MOVE _MEM_ equ endif ; MEM_MOVE % public _MEM_ _MEM_ proc \ dst:ptr byte, \ src:ptr byte, \ count:IWORD ; destination pointer ; source pointer ; number of bytes to copy ; push ebp ;U - save old frame pointer ; mov ebp, esp ;V - set new frame pointer push edi ;U - save edi push esi ;V - save esi mov esi,[src] ;U - esi = source mov ecx,[count] ;V - ecx = number of bytes to move mov edi,[dst] ;U - edi = dest ; ; Check for overlapping buffers: ; If (dst <= src) Or (dst >= src + Count) Then ; Do normal (Upwards) Copy ; Else ; Do Downwards Copy to avoid propagation ; mov eax,ecx ;V - eax = byte count... mov edx,ecx ;U - edx = byte count... add eax,esi ;V - eax = point past source end cmp edi,esi ;U - dst <= src ? jbe short CopyUp ;V - yes, copy toward higher addresses cmp edi,eax ;U - dst < (src + count) ? jb CopyDown ;V - yes, copy toward lower addresses ; ; Copy toward higher addresses. ; ; ; The algorithm for forward moves is to align the destination to a dword ; boundary and so we can move dwords with an aligned destination. This ; occurs in 3 steps. ; ; - move x = ((4 - Dest & 3) & 3) bytes ; - move y = ((L-x) >> 2) dwords ; - move (L - x - y*4) bytes ; CopyUp: test edi,11b ;U - destination dword aligned? jnz short CopyLeadUp ;V - if we are not dword aligned already, align shr ecx,2 ;U - shift down to dword count and edx,11b ;V - trailing byte count cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindUp ;V - if so, then jump rep movsd ;N - move all of our dwords jmp dword ptr TrailUpVec[edx*4] ;N - process trailing bytes ; ; Code to do optimal memory copies for non-dword-aligned destinations. ; ; The following length check is done for two reasons: ; ; 1. to ensure that the actual move length is greater than any possiale ; alignment move, and ; ; 2. to skip the multiple move logic for small moves where it would ; be faster to move the bytes with one instruction. ; align @WordSize CopyLeadUp: mov eax,edi ;U - get destination offset mov edx,11b ;V - prepare for mask sub ecx,4 ;U - check for really short string - sub for adjust jb short ByteCopyUp ;V - branch to just copy bytes and eax,11b ;U - get offset within first dword add ecx,eax ;V - update size after leading bytes copied jmp dword ptr LeadUpVec[eax*4-4] ;N - process leading bytes align @WordSize ByteCopyUp: jmp dword ptr TrailUpVec[ecx*4+16] ;N - process just bytes align @WordSize CopyUnwindUp: jmp dword ptr UnwindUpVec[ecx*4] ;N - unwind dword copy align @WordSize LeadUpVec dd LeadUp1, LeadUp2, LeadUp3 align @WordSize LeadUp1: and edx,ecx ;U - trailing byte count mov al,[esi] ;V - get first byte from source mov [edi],al ;U - write second byte to destination mov al,[esi+1] ;V - get second byte from source mov [edi+1],al ;U - write second byte to destination mov al,[esi+2] ;V - get third byte from source shr ecx,2 ;U - shift down to dword count mov [edi+2],al ;V - write third byte to destination add esi,3 ;U - advance source pointer add edi,3 ;V - advance destination pointer cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindUp ;V - if so, then jump rep movsd ;N - move all of our dwords jmp dword ptr TrailUpVec[edx*4] ;N - process trailing bytes align @WordSize LeadUp2: and edx,ecx ;U - trailing byte count mov al,[esi] ;V - get first byte from source mov [edi],al ;U - write second byte to destination mov al,[esi+1] ;V - get second byte from source shr ecx,2 ;U - shift down to dword count mov [edi+1],al ;V - write second byte to destination add esi,2 ;U - advance source pointer add edi,2 ;V - advance destination pointer cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindUp ;V - if so, then jump rep movsd ;N - move all of our dwords jmp dword ptr TrailUpVec[edx*4] ;N - process trailing bytes align @WordSize LeadUp3: and edx,ecx ;U - trailing byte count mov al,[esi] ;V - get first byte from source mov [edi],al ;U - write second byte to destination inc esi ;V - advance source pointer shr ecx,2 ;U - shift down to dword count inc edi ;V - advance destination pointer cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindUp ;V - if so, then jump rep movsd ;N - move all of our dwords jmp dword ptr TrailUpVec[edx*4] ;N - process trailing bytes align @WordSize UnwindUpVec dd UnwindUp0, UnwindUp1, UnwindUp2, UnwindUp3 dd UnwindUp4, UnwindUp5, UnwindUp6, UnwindUp7 UnwindUp7: mov eax,[esi+ecx*4-28] ;U - get dword from source ;V - spare mov [edi+ecx*4-28],eax ;U - put dword into destination UnwindUp6: mov eax,[esi+ecx*4-24] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-24],eax ;U - put dword into destination UnwindUp5: mov eax,[esi+ecx*4-20] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-20],eax ;U - put dword into destination UnwindUp4: mov eax,[esi+ecx*4-16] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-16],eax ;U - put dword into destination UnwindUp3: mov eax,[esi+ecx*4-12] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-12],eax ;U - put dword into destination UnwindUp2: mov eax,[esi+ecx*4-8] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-8],eax ;U - put dword into destination UnwindUp1: mov eax,[esi+ecx*4-4] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4-4],eax ;U - put dword into destination lea eax,[ecx*4] ;V - compute update for pointer add esi,eax ;U - update source pointer add edi,eax ;V - update destination pointer UnwindUp0: jmp dword ptr TrailUpVec[edx*4] ;N - process trailing bytes ;----------------------------------------------------------------------------- align @WordSize TrailUpVec dd TrailUp0, TrailUp1, TrailUp2, TrailUp3 align @WordSize TrailUp0: mov eax,[dst] ;U - return pointer to destination pop esi ;V - restore esi pop edi ;U - restore edi ;V - spare M_EXIT align @WordSize TrailUp1: mov al,[esi] ;U - get byte from source ;V - spare mov [edi],al ;U - put byte in destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT align @WordSize TrailUp2: mov al,[esi] ;U - get first byte from source ;V - spare mov [edi],al ;U - put first byte into destination mov al,[esi+1] ;V - get second byte from source mov [edi+1],al ;U - put second byte into destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT align @WordSize TrailUp3: mov al,[esi] ;U - get first byte from source ;V - spare mov [edi],al ;U - put first byte into destination mov al,[esi+1] ;V - get second byte from source mov [edi+1],al ;U - put second byte into destination mov al,[esi+2] ;V - get third byte from source mov [edi+2],al ;U - put third byte into destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT ;----------------------------------------------------------------------------- ;----------------------------------------------------------------------------- ;----------------------------------------------------------------------------- ; ; Copy down to avoid propogation in overlapping buffers. ; align @WordSize CopyDown: lea esi,[esi+ecx-4] ;U - point to 4 bytes before src buffer end lea edi,[edi+ecx-4] ;V - point to 4 bytes before dest buffer end ; ; See if the destination start is dword aligned ; test edi,11b ;U - test if dword aligned jnz short CopyLeadDown ;V - if not, jump shr ecx,2 ;U - shift down to dword count and edx,11b ;V - trailing byte count cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindDown ;V - if so, then jump std ;N - set direction flag rep movsd ;N - move all of our dwords cld ;N - clear direction flag back jmp dword ptr TrailDownVec[edx*4] ;N - process trailing bytes align @WordSize CopyUnwindDown: neg ecx ;U - negate dword count for table merging ;V - spare jmp dword ptr UnwindDownVec[ecx*4+28] ;N - unwind copy align @WordSize CopyLeadDown: mov eax,edi ;U - get destination offset mov edx,11b ;V - prepare for mask cmp ecx,4 ;U - check for really short string jb short ByteCopyDown ;V - branch to just copy bytes and eax,11b ;U - get offset within first dword sub ecx,eax ;U - to update size after lead copied jmp dword ptr LeadDownVec[eax*4-4] ;N - process leading bytes align @WordSize ByteCopyDown: jmp dword ptr TrailDownVec[ecx*4] ;N - process just bytes align @WordSize LeadDownVec dd LeadDown1, LeadDown2, LeadDown3 align @WordSize LeadDown1: mov al,[esi+3] ;U - load first byte and edx,ecx ;V - trailing byte count mov [edi+3],al ;U - write out first byte dec esi ;V - point to last src dword shr ecx,2 ;U - shift down to dword count dec edi ;V - point to last dest dword cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindDown ;V - if so, then jump std ;N - set direction flag rep movsd ;N - move all of our dwords cld ;N - clear direction flag jmp dword ptr TrailDownVec[edx*4] ;N - process trailing bytes align @WordSize LeadDown2: mov al,[esi+3] ;U - load first byte and edx,ecx ;V - trailing byte count mov [edi+3],al ;U - write out first byte mov al,[esi+2] ;V - get second byte from source shr ecx,2 ;U - shift down to dword count mov [edi+2],al ;V - write second byte to destination sub esi,2 ;U - point to last src dword sub edi,2 ;V - point to last dest dword cmp ecx,8 ;U - test if small enough for unwind copy jb short CopyUnwindDown ;V - if so, then jump std ;N - set direction flag rep movsd ;N - move all of our dwords cld ;N - clear direction flag jmp dword ptr TrailDownVec[edx*4] ;N - process trailing bytes align @WordSize LeadDown3: mov al,[esi+3] ;U - load first byte and edx,ecx ;V - trailing byte count mov [edi+3],al ;U - write out first byte mov al,[esi+2] ;V - get second byte from source mov [edi+2],al ;U - write second byte to destination mov al,[esi+1] ;V - get third byte from source shr ecx,2 ;U - shift down to dword count mov [edi+1],al ;V - write third byte to destination sub esi,3 ;U - point to last src dword sub edi,3 ;V - point to last dest dword cmp ecx,8 ;U - test if small enough for unwind copy jb CopyUnwindDown ;V - if so, then jump std ;N - set direction flag rep movsd ;N - move all of our dwords cld ;N - clear direction flag jmp dword ptr TrailDownVec[edx*4] ;N - process trailing bytes ;------------------------------------------------------------------ align @WordSize UnwindDownVec dd UnwindDown7, UnwindDown6, UnwindDown5, UnwindDown4 dd UnwindDown3, UnwindDown2, UnwindDown1, UnwindDown0 UnwindDown7: mov eax,[esi+ecx*4+28] ;U - get dword from source ;V - spare mov [edi+ecx*4+28],eax ;U - put dword into destination UnwindDown6: mov eax,[esi+ecx*4+24] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+24],eax ;U - put dword into destination UnwindDown5: mov eax,[esi+ecx*4+20] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+20],eax ;U - put dword into destination UnwindDown4: mov eax,[esi+ecx*4+16] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+16],eax ;U - put dword into destination UnwindDown3: mov eax,[esi+ecx*4+12] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+12],eax ;U - put dword into destination UnwindDown2: mov eax,[esi+ecx*4+8] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+8],eax ;U - put dword into destination UnwindDown1: mov eax,[esi+ecx*4+4] ;U(entry)/V(not) - get dword from source ;V(entry) - spare mov [edi+ecx*4+4],eax ;U - put dword into destination lea eax,[ecx*4] ;V - compute update for pointer add esi,eax ;U - update source pointer add edi,eax ;V - update destination pointer UnwindDown0: jmp dword ptr TrailDownVec[edx*4] ;N - process trailing bytes ;----------------------------------------------------------------------------- align @WordSize TrailDownVec dd TrailDown0, TrailDown1, TrailDown2, TrailDown3 align @WordSize TrailDown0: mov eax,[dst] ;U - return pointer to destination ;V - spare pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT align @WordSize TrailDown1: mov al,[esi+3] ;U - get byte from source ;V - spare mov [edi+3],al ;U - put byte in destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT align @WordSize TrailDown2: mov al,[esi+3] ;U - get first byte from source ;V - spare mov [edi+3],al ;U - put first byte into destination mov al,[esi+2] ;V - get second byte from source mov [edi+2],al ;U - put second byte into destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT align @WordSize TrailDown3: mov al,[esi+3] ;U - get first byte from source ;V - spare mov [edi+3],al ;U - put first byte into destination mov al,[esi+2] ;V - get second byte from source mov [edi+2],al ;U - put second byte into destination mov al,[esi+1] ;V - get third byte from source mov [edi+1],al ;U - put third byte into destination mov eax,[dst] ;V - return pointer to destination pop esi ;U - restore esi pop edi ;V - restore edi M_EXIT _MEM_ endp end