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/* strchr with SSE4.2
Copyright (C) 2009, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <sysdep.h>
#include <init-arch.h>
/* Define multiple versions only for the definition in libc. */
#ifndef NOT_IN_libc
.text
ENTRY(strchr)
.type strchr, @gnu_indirect_function
cmpl $0, __cpu_features+KIND_OFFSET(%rip)
jne 1f
call __init_cpu_features
1: leaq __strchr_sse2(%rip), %rax
testl $bit_SSE4_2, __cpu_features+CPUID_OFFSET+index_SSE4_2(%rip)
jz 2f
leaq __strchr_sse42(%rip), %rax
ret
2: testl $bit_Slow_BSF, __cpu_features+FEATURE_OFFSET+index_Slow_BSF(%rip)
jz 3f
leaq __strchr_sse2_no_bsf(%rip), %rax
3: ret
END(strchr)
/*
This implementation uses SSE4 instructions to compare up to 16 bytes
at a time looking for the first occurrence of the character c in the
string s:
char *strchr (const char *s, int c);
We use 0xa:
_SIDD_SBYTE_OPS
| _SIDD_CMP_EQUAL_EACH
| _SIDD_LEAST_SIGNIFICANT
on pcmpistri to compare xmm/mem128
0 1 2 3 4 5 6 7 8 9 A B C D E F
X X X X X X X X X X X X X X X X
against xmm
0 1 2 3 4 5 6 7 8 9 A B C D E F
C C C C C C C C C C C C C C C C
to find out if the first 16byte data element has a byte C and the
offset of the first byte. There are 3 cases:
1. The first 16byte data element has the byte C at the offset X.
2. The first 16byte data element has EOS and doesn't have the byte C.
3. The first 16byte data element is valid and doesn't have the byte C.
Here is the table of ECX, CFlag, ZFlag and SFlag for 3 cases:
case ECX CFlag ZFlag SFlag
1 X 1 0/1 0
2 16 0 1 0
3 16 0 0 0
We exit from the loop for cases 1 and 2 with jbe which branches
when either CFlag or ZFlag is 1. If CFlag == 1, ECX has the offset
X for case 1. */
.section .text.sse4.2,"ax",@progbits
.align 16
.type __strchr_sse42, @function
__strchr_sse42:
cfi_startproc
CALL_MCOUNT
testb %sil, %sil
je __strend_sse4
pxor %xmm2, %xmm2
movd %esi, %xmm1
movl %edi, %ecx
pshufb %xmm2, %xmm1
andl $15, %ecx
movq %rdi, %r8
je L(aligned_start)
/* Handle unaligned string. */
andq $-16, %r8
movdqa (%r8), %xmm0
pcmpeqb %xmm0, %xmm2
pcmpeqb %xmm1, %xmm0
/* Find where NULL is. */
pmovmskb %xmm2, %edx
/* Check if there is a match. */
pmovmskb %xmm0, %esi
/* Remove the leading bytes. */
sarl %cl, %edx
sarl %cl, %esi
testl %esi, %esi
je L(unaligned_no_match)
/* Check which byte is a match. */
bsfl %esi, %eax
/* Is there a NULL? */
testl %edx, %edx
je L(unaligned_match)
bsfl %edx, %esi
cmpl %esi, %eax
/* Return NULL if NULL comes first. */
ja L(return_null)
L(unaligned_match):
addq %rdi, %rax
ret
.p2align 4
L(unaligned_no_match):
testl %edx, %edx
jne L(return_null)
/* Loop start on aligned string. */
L(loop):
addq $16, %r8
L(aligned_start):
pcmpistri $0x2, (%r8), %xmm1
jbe L(wrap)
addq $16, %r8
pcmpistri $0x2, (%r8), %xmm1
jbe L(wrap)
addq $16, %r8
pcmpistri $0x2, (%r8), %xmm1
jbe L(wrap)
addq $16, %r8
pcmpistri $0x2, (%r8), %xmm1
jbe L(wrap)
jmp L(loop)
L(wrap):
jc L(loop_exit)
/* Return NULL. */
L(return_null):
xorl %eax, %eax
ret
/* Loop exit. */
.p2align 4
L(loop_exit):
leaq (%r8,%rcx), %rax
ret
cfi_endproc
.size __strchr_sse42, .-__strchr_sse42
# undef ENTRY
# define ENTRY(name) \
.type __strchr_sse2, @function; \
.align 16; \
__strchr_sse2: cfi_startproc; \
CALL_MCOUNT
# undef END
# define END(name) \
cfi_endproc; .size __strchr_sse2, .-__strchr_sse2
# undef libc_hidden_builtin_def
/* It doesn't make sense to send libc-internal strchr calls through a PLT.
The speedup we get from using SSE4.2 instruction is likely eaten away
by the indirect call in the PLT. */
# define libc_hidden_builtin_def(name) \
.globl __GI_strchr; __GI_strchr = __strchr_sse2
#endif
#include "../strchr.S"
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