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/* Optimized strcmp implementation for PowerPC64/POWER8.
Copyright (C) 2015-2024 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, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#ifndef STRCMP
# define STRCMP strcmp
#endif
/* Implements the function
size_t [r3] strcmp (const char *s1 [r3], const char *s2 [r4])
The implementation uses unaligned doubleword access to avoid specialized
code paths depending of data alignment. Although recent powerpc64 uses
64K as default, the page cross handling assumes minimum page size of
4k. */
.machine power8
ENTRY_TOCLESS (STRCMP, 4)
li r0,0
/* Check if [s1]+16 or [s2]+16 will cross a 4K page boundary using
the code:
(((size_t) s1) % PAGE_SIZE > (PAGE_SIZE - ITER_SIZE))
with PAGE_SIZE being 4096 and ITER_SIZE begin 16. */
rldicl r7,r3,0,52
rldicl r9,r4,0,52
cmpldi cr7,r7,4096-16
bgt cr7,L(pagecross_check)
cmpldi cr5,r9,4096-16
bgt cr5,L(pagecross_check)
/* For short string up to 16 bytes, load both s1 and s2 using
unaligned dwords and compare. */
ld r8,0(r3)
ld r10,0(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
ld r8,8(r3)
ld r10,8(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
addi r7,r3,16
addi r4,r4,16
L(align_8b):
/* Now it has checked for first 16 bytes, align source1 to doubleword
and adjust source2 address. */
rldicl r9,r7,0,61 /* source1 alignment to doubleword */
subf r4,r9,r4 /* Adjust source2 address based on source1
alignment. */
rldicr r7,r7,0,60 /* Align source1 to doubleword. */
/* At this point, source1 alignment is 0 and source2 alignment is
between 0 and 7. Check is source2 alignment is 0, meaning both
sources have the same alignment. */
andi. r9,r4,0x7
bne cr0,L(loop_diff_align)
/* If both source1 and source2 are doubleword aligned, there is no
need for page boundary cross checks. */
ld r8,0(r7)
ld r10,0(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
.align 4
L(loop_equal_align):
ld r8,8(r7)
ld r10,8(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
ld r8,16(r7)
ld r10,16(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
ldu r8,24(r7)
ldu r10,24(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
b L(loop_equal_align)
/* A zero byte was found in r8 (s1 dword), r9 contains the cmpb
result and r10 the dword from s2. To code isolate the byte
up to end (including the '\0'), masking with 0xFF the remaining
ones:
#if __LITTLE_ENDIAN__
(__builtin_ffsl (x) - 1) = counting trailing zero bits
r9 = (__builtin_ffsl (r9) - 1) + 8;
r9 = -1UL << r9
#else
r9 = __builtin_clzl (r9) + 8;
r9 = -1UL >> r9
#endif
r8 = r8 | r9
r10 = r10 | r9 */
#ifdef __LITTLE_ENDIAN__
nor r9,r9,r9
L(different_nocmpb):
neg r3,r9
and r9,r9,r3
cntlzd r9,r9
subfic r9,r9,63
#else
not r9,r9
L(different_nocmpb):
cntlzd r9,r9
subfic r9,r9,56
#endif
srd r3,r8,r9
srd r10,r10,r9
rldicl r10,r10,0,56
rldicl r3,r3,0,56
subf r3,r10,r3
extsw r3,r3
blr
.align 4
L(pagecross_check):
subfic r9,r9,4096
subfic r7,r7,4096
cmpld cr7,r7,r9
bge cr7,L(pagecross)
mr r7,r9
/* If unaligned 16 bytes reads across a 4K page boundary, it uses
a simple byte a byte comparison until the page alignment for s1
is reached. */
L(pagecross):
add r7,r3,r7
subf r9,r3,r7
mtctr r9
.align 4
L(pagecross_loop):
/* Loads a byte from s1 and s2, compare if *s1 is equal to *s2
and if *s1 is '\0'. */
lbz r9,0(r3)
lbz r10,0(r4)
addi r3,r3,1
addi r4,r4,1
cmplw cr7,r9,r10
cmpdi cr5,r9,r0
bne cr7,L(pagecross_ne)
beq cr5,L(pagecross_nullfound)
bdnz L(pagecross_loop)
b L(align_8b)
.align 4
/* The unaligned read of source2 will cross a 4K page boundary,
and the different byte or NULL maybe be in the remaining page
bytes. Since it can not use the unaligned load, the algorithm
reads and compares 8 bytes to keep source1 doubleword aligned. */
L(check_source2_byte):
li r9,8
mtctr r9
.align 4
L(check_source2_byte_loop):
lbz r9,0(r7)
lbz r10,0(r4)
addi r7,r7,1
addi r4,r4,1
cmplw cr7,r9,10
cmpdi r5,r9,0
bne cr7,L(pagecross_ne)
beq cr5,L(pagecross_nullfound)
bdnz L(check_source2_byte_loop)
/* If source2 is unaligned to doubleword, the code needs to check
on each iteration if the unaligned doubleword access will cross
a 4k page boundary. */
.align 5
L(loop_unaligned):
ld r8,0(r7)
ld r10,0(r4)
cmpb r12,r8,r0
cmpb r11,r8,r10
orc. r9,r12,r11
bne cr0,L(different_nocmpb)
addi r7,r7,8
addi r4,r4,8
L(loop_diff_align):
/* Check if [src2]+8 cross a 4k page boundary:
srcin2 % PAGE_SIZE > (PAGE_SIZE - 8)
with PAGE_SIZE being 4096. */
rldicl r9,r4,0,52
cmpldi cr7,r9,4088
ble cr7,L(loop_unaligned)
b L(check_source2_byte)
.align 4
L(pagecross_ne):
extsw r3,r9
mr r9,r10
L(pagecross_retdiff):
subf r9,r9,r3
extsw r3,r9
blr
.align 4
L(pagecross_nullfound):
li r3,0
b L(pagecross_retdiff)
END (STRCMP)
libc_hidden_builtin_def (strcmp)
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