minix/lib/libc/arch/i386/string/memset.S

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/* memset() Author: Kees J. Bot */
/* 2 Jan 1994 */
/* void *memset(void *s, int c, size_t n) */
/* Set a chunk of memory to the same byte value. */
/* */
#include <machine/asm.h>
ENTRY(memset)
push %ebp
movl %esp, %ebp
push %edi
movl 8(%ebp), %edi /* The string */
movzbl 12(%ebp), %eax /* The fill byte */
movl 16(%ebp), %ecx /* Length */
cld
cmpl $16, %ecx
jb sbyte /* Don't bother being smart with short arrays */
testl $1, %edi
jne sbyte /* Bit 0 set, use byte store */
testl $2, %edi
jne sword /* Bit 1 set, use word store */
slword:
movb %al, %ah
movl %eax, %edx
sall $16, %edx
orl %edx, %eax /* One byte to four bytes */
shrdl $2, %ecx, %edx /* Save low two bits of ecx in edx */
shrl $2, %ecx
rep stosl /* Store longwords. */
shldl $2, %edx, %ecx /* Restore low two bits */
sword:
movb %al, %ah /* One byte to two bytes */
shrl $1, %ecx
rep stosw /* Store words */
adcl %ecx, %ecx /* One more byte? */
sbyte:
rep stosb /* Store bytes */
done:
movl 8(%ebp), %eax /* Return some value you have no need for */
pop %edi
pop %ebp
ret