/*
* Written by J.T. Conklin <
[email protected]>
* Public domain.
*/
#include <machine/asm.h>
#if defined(LIBC_SCCS)
RCSID("$NetBSD: strchr.S,v 1.3 2014/03/22 19:38:46 jakllsch Exp $")
#endif
ENTRY(strchr)
pushl %esi
pushl %ebx
movl 12(%esp),%eax
movzbl 16(%esp),%ecx
/*
* Align to word boundary.
* Consider unrolling loop?
*/
Lalign:
testb $3,%al
je .Lword_aligned
movb (%eax),%bl
cmpb %cl,%bl
je .Ldone
testb %bl,%bl
je .Lzero
incl %eax
jmp .Lalign
Lword_aligned:
/* copy char to all bytes in word */
movb %cl,%ch
movl %ecx,%edx
sall $16,%ecx
orl %edx,%ecx
/* Check whether any byte in the word is equal to ch or 0. */
_ALIGN_TEXT
Lloop:
movl (%eax),%ebx
addl $4,%eax
movl %ebx,%esi
leal -0x01010101(%ebx),%edx
xorl %ecx,%esi
subl $0x01010101,%esi
orl %esi,%edx
testl $0x80808080,%edx
je .Lloop
/*
* In rare cases, the above loop may exit prematurely. We must
* return to the loop if none of the bytes in the word match
* ch or are equal to 0.
*/
/*
* Alignment here avoids a stall on the Athlon, even though
* it's not a branch target.
*/
_ALIGN_TEXT
cmpb %cl,%bl /* 1st byte == ch? */
jne 1f
subl $4,%eax
jmp .Ldone
1: testb %bl,%bl /* 1st byte == 0? */
je .Lzero
cmpb %cl,%bh /* 2nd byte == ch? */
jne 1f
subl $3,%eax
jmp .Ldone
1: testb %bh,%bh /* 2nd byte == 0? */
je .Lzero
shrl $16,%ebx
cmpb %cl,%bl /* 3rd byte == ch? */
jne 1f
subl $2,%eax
jmp .Ldone
1: testb %bl,%bl /* 3rd byte == 0? */
je .Lzero
cmpb %cl,%bh /* 4th byte == ch? */
jne 1f
decl %eax
jmp .Ldone
1: testb %bh,%bh /* 4th byte == 0? */
jne .Lloop
Lzero:
/* If a ch wasn't found, return 0. */
xorl %eax,%eax
Ldone:
popl %ebx
popl %esi
ret
END(strchr)
STRONG_ALIAS(index,strchr)
