Category : C++ Source Code
Archive   : VCCRT2.ZIP
Filename : MEMSET.ASM

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) 1985-1992, Microsoft Corporation. All rights reserved.
;
;Purpose:
; contains the memset() routine
;
;*******************************************************************************

.xlist
include version.inc
include cmacros.inc
.list

sBegin code

assumes cs,code
assumes ds,data

page
;***
;char *memset(dst, val, count) - sets "count" bytes at "dst" to "val"
;
;Purpose:
; Sets the first "count" bytes of the memory starting
; at "dst" to the character value "val".
;
; Algorithm:
; char *
; memset (dst, val, count)
; char *dst;
; char val;
; unsigned int count;
; {
; char *start = dst;
;
; while (count--)
; *dst++ = val;
; return(start);
; }
;
;Entry:
; char *dst - pointer to memory to fill with val
; char val - value to put in dst bytes
; int count - number of bytes of dst to fill
;
;Exit:
; returns dst, with filled bytes
;
;Uses:
;
;Exceptions:
;
;*******************************************************************************

ifdef MODELINDEP

cProc _fmemset,,<>

else

cProc memset,,<>

endif

parmDP dst
parmB value
parmW count

cBegin
mov dx,di ; Preserve DI

if sizeD
les di,dst ; ES:DI = dst
else
mov ax,ds
mov es,ax
mov di,dst ; ES:DI = dst
endif
mov bx,di ; save a copy of DST

mov cx,count
jcxz toend ; if no work to do

mov al,value ; the byte value to be stored
mov ah,al ; store it as a word

test di,1 ; is dst address odd?
jz dowords ; yes: proceed

stosb ; no: store first byte to get word alignment
dec cx
dowords:
shr cx,1
rep stosw ; store word at a time
adc cx,cx
rep stosb ; store final ("odd") byte if necessary
toend:
mov di,dx ; Restore DI

xchg ax,bx ; AX = dst
if sizeD
mov dx,es ; segment part of addr
endif
pop bp
ret
cEnd

sEnd

end