strchr.s

操作系统源代码

!	strchr()					Author: Kees J. Bot
!								1 Jan 1994
.sect .text; .sect .rom; .sect .data; .sect .bss

! char *strchr(const char *s, int c)
!	Look for a character in a string.
!
.sect .text
.define _strchr
	.align	16
_strchr:
	push	ebp
	mov	ebp, esp
	push	edi
	cld
	mov	edi, 8(ebp)	! edi = string
	mov	edx, 16		! Look at small chunks of the string
next:	shl	edx, 1		! Chunks become bigger each time
	mov	ecx, edx
	xorb	al, al		! Look for the zero at the end
	repne
	scasb
	pushf			! Remember the flags
	sub	ecx, edx
	neg	ecx		! Some or all of the chunk
	sub	edi, ecx	! Step back
	movb	al, 12(ebp)	! The character to look for
	repne
	scasb
	je	found
	popf			! Did we find the end of string earlier?
	jne	next		! No, try again
	xor	eax, eax	! Return NULL
	pop	edi
	pop	ebp
	ret
found:	pop	eax		! Get rid of those flags
	lea	eax, -1(edi)	! Address of byte found
	pop	edi
	pop	ebp
	ret