328 lines
6.7 KiB
ArmAsm
328 lines
6.7 KiB
ArmAsm
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/* Optimized strncmp implementation for PowerPC64/POWER8.
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Copyright (C) 2015-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#ifndef STRNCMP
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# define STRNCMP strncmp
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#endif
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/* Implements the function
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int [r3] strncmp (const char *s1 [r3], const char *s2 [r4], size_t [r5] n)
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The implementation uses unaligned doubleword access to avoid specialized
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code paths depending of data alignment. Although recent powerpc64 uses
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64K as default, the page cross handling assumes minimum page size of
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4k. */
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.machine power8
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ENTRY_TOCLESS (STRNCMP, 4)
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/* Check if size is 0. */
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mr. r10,r5
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beq cr0,L(ret0)
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/* Check if [s1]+16 or [s2]+16 will cross a 4K page boundary using
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the code:
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(((size_t) s1) % PAGE_SIZE > (PAGE_SIZE - ITER_SIZE))
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with PAGE_SIZE being 4096 and ITER_SIZE begin 16. */
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rldicl r8,r3,0,52
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cmpldi cr7,r8,4096-16
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bgt cr7,L(pagecross)
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rldicl r9,r4,0,52
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cmpldi cr7,r9,4096-16
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bgt cr7,L(pagecross)
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/* For short string up to 16 bytes, load both s1 and s2 using
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unaligned dwords and compare. */
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ld r7,0(r3)
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ld r9,0(r4)
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li r8,0
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cmpb r8,r7,r8
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cmpb r6,r7,r9
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orc. r8,r8,r6
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bne cr0,L(different1)
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/* If the string compared are equal, but size is less or equal
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to 8, return 0. */
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cmpldi cr7,r10,8
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li r9,0
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ble cr7,L(ret1)
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addi r5,r10,-8
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ld r7,8(r3)
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ld r9,8(r4)
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cmpb r8,r7,r8
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cmpb r6,r7,r9
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orc. r8,r8,r6
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bne cr0,L(different0)
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cmpldi cr7,r5,8
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mr r9,r8
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ble cr7,L(ret1)
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/* Update pointers and size. */
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addi r10,r10,-16
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addi r3,r3,16
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addi r4,r4,16
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/* Now it has checked for first 16 bytes, align source1 to doubleword
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and adjust source2 address. */
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L(align_8b):
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rldicl r5,r3,0,61
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rldicr r3,r3,0,60
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subf r4,r5,r4
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add r10,r10,r5
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/* At this point, source1 alignment is 0 and source2 alignment is
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between 0 and 7. Check is source2 alignment is 0, meaning both
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sources have the same alignment. */
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andi. r8,r4,0x7
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beq cr0,L(loop_eq_align_0)
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li r5,0
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b L(loop_ne_align_1)
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/* If source2 is unaligned to doubleword, the code needs to check
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on each interation if the unaligned doubleword access will cross
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a 4k page boundary. */
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.align 4
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L(loop_ne_align_0):
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ld r7,0(r3)
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ld r9,0(r4)
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cmpb r8,r7,r5
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cmpb r6,r7,r9
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orc. r8,r8,r6
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bne cr0,L(different1)
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cmpldi cr7,r10,8
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ble cr7,L(ret0)
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addi r10,r10,-8
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addi r3,r3,8
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addi r4,r4,8
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L(loop_ne_align_1):
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rldicl r9,r4,0,52
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cmpldi r7,r9,4088
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ble cr7,L(loop_ne_align_0)
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cmpdi cr7,r10,0
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beq cr7,L(ret0)
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lbz r9,0(r3)
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lbz r8,0(r4)
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cmplw cr7,r9,r8
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bne cr7,L(byte_ne_4)
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cmpdi cr7,r9,0
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beq cr7,L(size_reached_0)
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li r9,r7
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addi r8,r3,1
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mtctr r9
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addi r4,r4,1
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addi r10,r10,-1
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addi r3,r3,8
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/* The unaligned read of source2 will cross a 4K page boundary,
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and the different byte or NULL maybe be in the remaining page
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bytes. Since it can not use the unaligned load the algorithm
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reads and compares 8 bytes to keep source1 doubleword aligned. */
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.align 4
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L(loop_ne_align_byte):
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cmpdi cr7,r10,0
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addi r10,r10,-1
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beq cr7,L(ret0)
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lbz r9,0(r8)
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lbz r7,0(r4)
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addi r8,r8,1
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addi r4,r4,1
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cmplw cr7,r9,r7
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cmpdi cr5,r9,0
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bne cr7,L(size_reached_2)
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beq cr5,L(size_reached_0)
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bdnz L(loop_ne_align_byte)
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cmpdi cr7,r10,0
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bne+ cr7,L(loop_ne_align_0)
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.align 4
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L(ret0):
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li r9,0
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L(ret1):
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mr r3,r9
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blr
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/* The code now check if r8 and r10 are different by issuing a
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cmpb and shift the result based on its output:
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#ifdef __LITTLE_ENDIAN__
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leadzero = (__builtin_ffsl (z1) - 1);
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leadzero = leadzero > (n-1)*8 ? (n-1)*8 : leadzero;
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r1 = (r1 >> leadzero) & 0xFFUL;
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r2 = (r2 >> leadzero) & 0xFFUL;
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#else
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leadzero = __builtin_clzl (z1);
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leadzero = leadzero > (n-1)*8 ? (n-1)*8 : leadzero;
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r1 = (r1 >> (56 - leadzero)) & 0xFFUL;
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r2 = (r2 >> (56 - leadzero)) & 0xFFUL;
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#endif
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return r1 - r2; */
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.align 4
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L(different0):
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mr r10,r5
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#ifdef __LITTLE_ENDIAN__
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L(different1):
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neg r11,r8
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sldi r10,r10,3
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and r8,r11,r8
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addi r10,r10,-8
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cntlzd r8,r8
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subfic r8,r8,63
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extsw r8,r8
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cmpld cr7,r8,r10
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ble cr7,L(different2)
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mr r8,r10
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L(different2):
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extsw r8,r8
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#else
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L(different1):
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addi r10,r10,-1
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cntlzd r8,r8
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sldi r10,r10,3
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cmpld cr7,r8,r10
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blt cr7,L(different2)
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mr r8,r10
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L(different2):
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subfic r8,r8,56
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#endif
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srd r7,r7,r8
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srd r9,r9,r8
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rldicl r3,r7,0,56
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rldicl r9,r9,0,56
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subf r9,r9,3
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extsw r9,r9
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mr r3,r9
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blr
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/* If unaligned 16 bytes reads across a 4K page boundary, it uses
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a simple byte a byte comparison until the page alignment for s1
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is reached. */
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.align 4
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L(pagecross):
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lbz r7,0(r3)
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lbz r9,0(r4)
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subfic r8,r8,4095
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cmplw cr7,r9,r7
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bne cr7,L(byte_ne_3)
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cmpdi cr7,r9,0
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beq cr7,L(byte_ne_0)
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addi r10,r10,-1
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subf r7,r8,r10
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subf r9,r7,r10
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addi r9,r9,1
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mtctr r9
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b L(pagecross_loop1)
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.align 4
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L(pagecross_loop0):
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beq cr7,L(ret0)
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lbz r9,0(r3)
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lbz r8,0(r4)
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addi r10,r10,-1
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cmplw cr7,r9,r8
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cmpdi cr5,r9,0
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bne r7,L(byte_ne_2)
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beq r5,L(byte_ne_0)
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L(pagecross_loop1):
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cmpdi cr7,r10,0
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addi r3,r3,1
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addi r4,r4,1
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bdnz L(pagecross_loop0)
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cmpdi cr7,r7,0
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li r9,0
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bne+ cr7,L(align_8b)
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b L(ret1)
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/* If both source1 and source2 are doubleword aligned, there is no
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need for page boundary cross checks. */
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.align 4
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L(loop_eq_align_0):
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ld r7,0(r3)
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ld r9,0(r4)
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cmpb r8,r7,r8
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cmpb r6,r7,r9
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orc. r8,r8,r6
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bne cr0,L(different1)
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cmpldi cr7,r10,8
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ble cr7,L(ret0)
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addi r9,r10,-9
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li r5,0
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srdi r9,r9,3
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addi r9,r9,1
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mtctr r9
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b L(loop_eq_align_2)
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.align 4
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L(loop_eq_align_1):
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bdz L(ret0)
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L(loop_eq_align_2):
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ldu r7,8(r3)
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addi r10,r10,-8
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ldu r9,8(r4)
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cmpb r8,r7,r5
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cmpb r6,r7,r9
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orc. r8,r8,r6
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beq cr0,L(loop_eq_align_1)
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b L(different1)
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.align 4
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L(byte_ne_0):
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li r7,0
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L(byte_ne_1):
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subf r9,r9,r7
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extsw r9,r9
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b L(ret1)
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.align 4
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L(byte_ne_2):
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extsw r7,r9
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mr r9,r8
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b L(byte_ne_1)
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L(size_reached_0):
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li r10,0
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L(size_reached_1):
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subf r9,r9,r10
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extsw r9,r9
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b L(ret1)
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L(size_reached_2):
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extsw r10,r9
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mr r9,r7
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b L(size_reached_1)
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L(byte_ne_3):
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extsw r7,r7
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b L(byte_ne_1)
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L(byte_ne_4):
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extsw r10,r9
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mr r9,r8
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b L(size_reached_1)
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END(STRNCMP)
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libc_hidden_builtin_def(strncmp)
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