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/* Optimized strncmp implementation for PowerPC64/POWER8.
Copyright (C) 2015-2023 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 STRNCMP
# define STRNCMP strncmp
#endif
/* Implements the function
int [r3] strncmp (const char *s1 [r3], const char *s2 [r4], size_t [r5] n)
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 (STRNCMP, 4)
/* Check if size is 0. */
mr. r10,r5
beq cr0,L(ret0)
/* 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 r8,r3,0,52
cmpldi cr7,r8,4096-16
bgt cr7,L(pagecross)
rldicl r9,r4,0,52
cmpldi cr7,r9,4096-16
bgt cr7,L(pagecross)
/* For short string up to 16 bytes, load both s1 and s2 using
unaligned dwords and compare. */
ld r7,0(r3)
ld r9,0(r4)
li r8,0
cmpb r8,r7,r8
cmpb r6,r7,r9
orc. r8,r8,r6
bne cr0,L(different1)
/* If the string compared are equal, but size is less or equal
to 8, return 0. */
cmpldi cr7,r10,8
li r9,0
ble cr7,L(ret1)
addi r5,r10,-8
ld r7,8(r3)
ld r9,8(r4)
cmpb r8,r7,r8
cmpb r6,r7,r9
orc. r8,r8,r6
bne cr0,L(different0)
cmpldi cr7,r5,8
mr r9,r8
ble cr7,L(ret1)
/* Update pointers and size. */
addi r10,r10,-16
addi r3,r3,16
addi r4,r4,16
/* Now it has checked for first 16 bytes, align source1 to doubleword
and adjust source2 address. */
L(align_8b):
rldicl r5,r3,0,61
rldicr r3,r3,0,60
subf r4,r5,r4
add r10,r10,r5
/* 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. r8,r4,0x7
beq cr0,L(loop_eq_align_0)
li r5,0
b L(loop_ne_align_1)
/* If source2 is unaligned to doubleword, the code needs to check
on each interation if the unaligned doubleword access will cross
a 4k page boundary. */
.align 4
L(loop_ne_align_0):
ld r7,0(r3)
ld r9,0(r4)
cmpb r8,r7,r5
cmpb r6,r7,r9
orc. r8,r8,r6
bne cr0,L(different1)
cmpldi cr7,r10,8
ble cr7,L(ret0)
addi r10,r10,-8
addi r3,r3,8
addi r4,r4,8
L(loop_ne_align_1):
rldicl r9,r4,0,52
cmpldi r7,r9,4088
ble cr7,L(loop_ne_align_0)
cmpdi cr7,r10,0
beq cr7,L(ret0)
lbz r9,0(r3)
lbz r8,0(r4)
cmplw cr7,r9,r8
bne cr7,L(byte_ne_4)
cmpdi cr7,r9,0
beq cr7,L(size_reached_0)
li r9,r7
addi r8,r3,1
mtctr r9
addi r4,r4,1
addi r10,r10,-1
addi r3,r3,8
/* 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. */
.align 4
L(loop_ne_align_byte):
cmpdi cr7,r10,0
addi r10,r10,-1
beq cr7,L(ret0)
lbz r9,0(r8)
lbz r7,0(r4)
addi r8,r8,1
addi r4,r4,1
cmplw cr7,r9,r7
cmpdi cr5,r9,0
bne cr7,L(size_reached_2)
beq cr5,L(size_reached_0)
bdnz L(loop_ne_align_byte)
cmpdi cr7,r10,0
bne+ cr7,L(loop_ne_align_0)
.align 4
L(ret0):
li r9,0
L(ret1):
mr r3,r9
blr
/* The code now check if r8 and r10 are different by issuing a
cmpb and shift the result based on its output:
#ifdef __LITTLE_ENDIAN__
leadzero = (__builtin_ffsl (z1) - 1);
leadzero = leadzero > (n-1)*8 ? (n-1)*8 : leadzero;
r1 = (r1 >> leadzero) & 0xFFUL;
r2 = (r2 >> leadzero) & 0xFFUL;
#else
leadzero = __builtin_clzl (z1);
leadzero = leadzero > (n-1)*8 ? (n-1)*8 : leadzero;
r1 = (r1 >> (56 - leadzero)) & 0xFFUL;
r2 = (r2 >> (56 - leadzero)) & 0xFFUL;
#endif
return r1 - r2; */
.align 4
L(different0):
mr r10,r5
#ifdef __LITTLE_ENDIAN__
L(different1):
neg r11,r8
sldi r10,r10,3
and r8,r11,r8
addi r10,r10,-8
cntlzd r8,r8
subfic r8,r8,63
extsw r8,r8
cmpld cr7,r8,r10
ble cr7,L(different2)
mr r8,r10
L(different2):
extsw r8,r8
#else
L(different1):
addi r10,r10,-1
cntlzd r8,r8
sldi r10,r10,3
cmpld cr7,r8,r10
blt cr7,L(different2)
mr r8,r10
L(different2):
subfic r8,r8,56
#endif
srd r7,r7,r8
srd r9,r9,r8
rldicl r3,r7,0,56
rldicl r9,r9,0,56
subf r9,r9,3
extsw r9,r9
mr r3,r9
blr
/* 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. */
.align 4
L(pagecross):
lbz r7,0(r3)
lbz r9,0(r4)
subfic r8,r8,4095
cmplw cr7,r9,r7
bne cr7,L(byte_ne_3)
cmpdi cr7,r9,0
beq cr7,L(byte_ne_0)
addi r10,r10,-1
subf r7,r8,r10
subf r9,r7,r10
addi r9,r9,1
mtctr r9
b L(pagecross_loop1)
.align 4
L(pagecross_loop0):
beq cr7,L(ret0)
lbz r9,0(r3)
lbz r8,0(r4)
addi r10,r10,-1
cmplw cr7,r9,r8
cmpdi cr5,r9,0
bne r7,L(byte_ne_2)
beq r5,L(byte_ne_0)
L(pagecross_loop1):
cmpdi cr7,r10,0
addi r3,r3,1
addi r4,r4,1
bdnz L(pagecross_loop0)
cmpdi cr7,r7,0
li r9,0
bne+ cr7,L(align_8b)
b L(ret1)
/* If both source1 and source2 are doubleword aligned, there is no
need for page boundary cross checks. */
.align 4
L(loop_eq_align_0):
ld r7,0(r3)
ld r9,0(r4)
cmpb r8,r7,r8
cmpb r6,r7,r9
orc. r8,r8,r6
bne cr0,L(different1)
cmpldi cr7,r10,8
ble cr7,L(ret0)
addi r9,r10,-9
li r5,0
srdi r9,r9,3
addi r9,r9,1
mtctr r9
b L(loop_eq_align_2)
.align 4
L(loop_eq_align_1):
bdz L(ret0)
L(loop_eq_align_2):
ldu r7,8(r3)
addi r10,r10,-8
ldu r9,8(r4)
cmpb r8,r7,r5
cmpb r6,r7,r9
orc. r8,r8,r6
beq cr0,L(loop_eq_align_1)
b L(different1)
.align 4
L(byte_ne_0):
li r7,0
L(byte_ne_1):
subf r9,r9,r7
extsw r9,r9
b L(ret1)
.align 4
L(byte_ne_2):
extsw r7,r9
mr r9,r8
b L(byte_ne_1)
L(size_reached_0):
li r10,0
L(size_reached_1):
subf r9,r9,r10
extsw r9,r9
b L(ret1)
L(size_reached_2):
extsw r10,r9
mr r9,r7
b L(size_reached_1)
L(byte_ne_3):
extsw r7,r7
b L(byte_ne_1)
L(byte_ne_4):
extsw r10,r9
mr r9,r8
b L(size_reached_1)
END(STRNCMP)
libc_hidden_builtin_def(strncmp)
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