1 /* $OpenBSD: memset.S,v 1.4 2014年11月29日 18:51:23 tedu 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(memset) 11 pushl %edi 12 pushl %ebx 13 movl 12(%esp),%edi 14 movzbl 16(%esp),%eax /* unsigned char, zero extend */ 15 movl 20(%esp),%ecx 16 pushl %edi /* push address of buffer */ 17 18 /* 19 * if the string is too short, it's really not worth the overhead 20 * of aligning to word boundaries, etc. So we jump to a plain 21 * unaligned set. 22 */ 23 cmpl $0x0f,%ecx 24 jle L1 25 26 movb %al,%ah /* copy char to all bytes in word */ 27 movl %eax,%edx 28 sall $16,%eax 29 orl %edx,%eax 30 31 movl %edi,%edx /* compute misalignment */ 32 negl %edx 33 andl $3,%edx 34 movl %ecx,%ebx 35 subl %edx,%ebx 36 37 movl %edx,%ecx /* set until word aligned */ 38 rep 39 stosb 40 41 movl %ebx,%ecx 42 shrl $2,%ecx /* set by words */ 43 rep 44 stosl 45 46 movl %ebx,%ecx /* set remainder by bytes */ 47 andl $3,%ecx 48 L1: rep 49 stosb 50 51 popl %eax /* pop address of buffer */ 52 popl %ebx 53 popl %edi 54 ret 55