1 /* $OpenBSD: bzero.S,v 1.6 2022年08月22日 09:33:40 jsg Exp $ */ 2 3 /* 4 * Written by J.T. Conklin <jtc@netbsd.org>. 5 * Public domain. 6 */ 7 8#include <machine/asm.h> 9 10 ENTRY(bzero) 11 pushl %edi 12 movl 8(%esp),%edi 13 movl 12(%esp),%edx 14 15 xorl %eax,%eax /* set fill data to 0 */ 16 17 /* 18 * if the string is too short, it's really not worth the overhead 19 * of aligning to word boundaries, etc. So we jump to a plain 20 * unaligned set. 21 */ 22 cmpl $16,%edx 23 jb L1 24 25 movl %edi,%ecx /* compute misalignment */ 26 negl %ecx 27 andl $3,%ecx 28 subl %ecx,%edx 29 rep /* zero until word aligned */ 30 stosb 31 32 movl %edx,%ecx /* zero by words */ 33 shrl $2,%ecx 34 andl $3,%edx 35 rep 36 stosl 37 38 L1: movl %edx,%ecx /* zero remainder by bytes */ 39 rep 40 stosb 41 42 popl %edi 43 ret 44