NetBSD/lib/libc/arch/i386/string/bzero.S

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/*
* Written by J.T. Conklin <jtc@netbsd.org>.
* Public domain.
*/
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#include <machine/asm.h>
#if defined(LIBC_SCCS)
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RCSID("$NetBSD: bzero.S,v 1.8 1995/04/28 22:57:58 jtc Exp $")
#endif
ENTRY(bzero)
pushl %edi
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movl 8(%esp),%edi
movl 12(%esp),%edx
cld /* set fill direction forward */
xorl %eax,%eax /* set fill data to 0 */
/*
* if the string is too short, it's really not worth the overhead
* of aligning to word boundries, etc. So we jump to a plain
* unaligned set.
*/
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cmpl $16,%edx
jb L1
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movl %edi,%ecx /* compute misalignment */
negl %ecx
andl $3,%ecx
subl %ecx,%edx
rep /* zero until word aligned */
stosb
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movl %edx,%ecx /* zero by words */
shrl $2,%ecx
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andl $3,%edx
rep
stosl
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L1: movl %edx,%ecx /* zero remainder by bytes */
rep
stosb
popl %edi
ret