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/* $OpenBSD: strrchr.S,v 1.3 2014/12/09 15:13:57 reyk Exp $ */
/* $NetBSD: strrchr.S,v 1.3 2014/03/22 19:16:34 jakllsch Exp $ */
/*
* Written by J.T. Conklin <jtc@acorntoolworks.com>
* Public domain.
*/
#include <machine/asm.h>
STRONG_ALIAS(rindex, strrchr)
ENTRY(strrchr)
movzbq %sil,%rcx
/* zero return value */
xorq %rax,%rax
/*
* Align to word boundary.
* Consider unrolling loop?
*/
.Lalign:
testb $7,%dil
je .Lword_aligned
movb (%rdi),%dl
cmpb %cl,%dl
cmoveq %rdi,%rax
incq %rdi
testb %dl,%dl
jne .Lalign
jmp .Ldone
.Lword_aligned:
/* copy char to all bytes in word */
movb %cl,%ch
movq %rcx,%rdx
salq $16,%rcx
orq %rdx,%rcx
movq %rcx,%rdx
salq $32,%rcx
orq %rdx,%rcx
movabsq $0x0101010101010101,%r8
movabsq $0x8080808080808080,%r9
/* Check whether any byte in the word is equal to ch or 0. */
_ALIGN_TEXT
.Lloop:
movq (%rdi),%rdx
addq $8,%rdi
movq %rdx,%rsi
subq %r8,%rdx
xorq %rcx,%rsi
subq %r8,%rsi
orq %rsi,%rdx
testq %r9,%rdx
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.
*/
movb -8(%rdi),%dl
cmpb %cl,%dl /* 1st byte == ch? */
jne 1f
leaq -8(%rdi),%rax
1: testb %dl,%dl /* 1st byte == 0? */
je .Ldone
movb -7(%rdi),%dl
cmpb %cl,%dl /* 2nd byte == ch? */
jne 1f
leaq -7(%rdi),%rax
1: testb %dl,%dl /* 2nd byte == 0? */
je .Ldone
movb -6(%rdi),%dl
cmpb %cl,%dl /* 3rd byte == ch? */
jne 1f
leaq -6(%rdi),%rax
1: testb %dl,%dl /* 3rd byte == 0? */
je .Ldone
movb -5(%rdi),%dl
cmpb %cl,%dl /* 4th byte == ch? */
jne 1f
leaq -5(%rdi),%rax
1: testb %dl,%dl /* 4th byte == 0? */
je .Ldone
movb -4(%rdi),%dl
cmpb %cl,%dl /* 5th byte == ch? */
jne 1f
leaq -4(%rdi),%rax
1: testb %dl,%dl /* 5th byte == 0? */
je .Ldone
movb -3(%rdi),%dl
cmpb %cl,%dl /* 6th byte == ch? */
jne 1f
leaq -3(%rdi),%rax
1: testb %dl,%dl /* 6th byte == 0? */
je .Ldone
movb -2(%rdi),%dl
cmpb %cl,%dl /* 7th byte == ch? */
jne 1f
leaq -2(%rdi),%rax
1: testb %dl,%dl /* 7th byte == 0? */
je .Ldone
movb -1(%rdi),%dl
cmpb %cl,%dl /* 8th byte == ch? */
jne 1f
leaq -1(%rdi),%rax
1: testb %dl,%dl /* 8th byte == 0? */
jne .Lloop
.Ldone:
ret
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