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page ,132 title memset - set sections of memory all to one byte;***;memset.asm - set a section of memory to all one byte;; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.;;Purpose:; contains the memset() routine;;Revision History:; 05-07-84 RN initial version; 06-30-87 SKS faster algorithm; 05-17-88 SJM Add model-independent (large model) ifdef; 08-04-88 SJM convert to cruntime/ add 32-bit support; 08-19-88 JCR Enable word alignment code for all models/CPUs,; Some code improvement; 10-25-88 JCR General cleanup for 386-only code; 10-27-88 JCR More optimization (dword alignment, no ebx usage, etc); 03-23-90 GJF Changed to _stdcall. Also, fixed the copyright.; 05-10-91 GJF Back to _cdecl, sigh...; 01-23-95 GJF Improved routine from Intel Israel. I fixed up the; formatting and comments.; 01-24-95 GJF Added FPO directive.; 06-12-01 PML inc->add 1, dec->sub 1 for Pentium 4 perf (vs7#267015);;*******************************************************************************
.xlist include cruntime.inc .list
page;***;char *memset(dst, value, count) - sets "count" bytes at "dst" to "value";;Purpose:; Sets the first "count" bytes of the memory starting; at "dst" to the character value "value".;; Algorithm:; char *; memset (dst, value, count); char *dst;; char value;; unsigned int count;; {; char *start = dst;;; while (count--); *dst++ = value;; return(start);; };;Entry:; char *dst - pointer to memory to fill with value; char value - value to put in dst bytes; int count - number of bytes of dst to fill;;Exit:; returns dst, with filled bytes;;Uses:;;Exceptions:;;*******************************************************************************
CODESEG
public memsetmemset proc
.FPO ( 0, 3, 0, 0, 0, 0 )
mov edx,[esp + 0ch] ; edx = "count" mov ecx,[esp + 4] ; ecx points to "dst" test edx,edx ; 0? jz short toend ; if so, nothing to do xor eax,eax mov al,[esp + 8] ; the byte "value" to be stored ; Align address on dword boundary push edi ; preserve edi mov edi,ecx ; edi = dest pointer cmp edx,4 ; if it's less then 4 bytes jb tail ; tail needs edi and edx to be initialized neg ecx and ecx,3 ; ecx = # bytes before dword boundary jz short dwords ; jump if address already aligned sub edx,ecx ; edx = adjusted count (for later)adjust_loop: mov [edi],al add edi,1 sub ecx,1 jnz adjust_loop dwords:; set all 4 bytes of eax to [value] mov ecx,eax ; ecx=0/0/0/value shl eax,8 ; eax=0/0/value/0 add eax,ecx ; eax=0/0val/val mov ecx,eax ; ecx=0/0/val/val shl eax,10h ; eax=val/val/0/0 add eax,ecx ; eax = all 4 bytes = [value] ; Set dword-sized blocks mov ecx,edx ; move original count to ecx and edx,3 ; prepare in edx byte count (for tail loop) shr ecx,2 ; adjust ecx to be dword count jz tail ; jump if it was less then 4 bytes rep stosdmain_loop_tail: test edx,edx ; if there is no tail bytes, jz finish ; we finish, and it's time to leave; Set remaining bytes tail: mov [edi],al ; set remaining bytes add edi,1 sub edx,1 ; if there is some more bytes jnz tail ; continue to fill them ; Donefinish: mov eax,[esp + 8] ; return dest pointer pop edi ; restore edi
ret
toend: mov eax,[esp + 4] ; return dest pointer ret memset endp
end
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