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/* SPDX-License-Identifier: GPL-2.0-only */
#include <linux/linkage.h>
#include <asm/asm.h>
#include <asm-generic/export.h>
#include <asm/alternative-macros.h>
#include <asm/errata_list.h>
/* int strncmp(const char *cs, const char *ct, size_t count) */
SYM_FUNC_START(strncmp)
ALTERNATIVE("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
/*
* Returns
* a0 - comparison result, value like strncmp
*
* Parameters
* a0 - string1
* a1 - string2
* a2 - number of characters to compare
*
* Clobbers
* t0, t1, t2
*/
li t2, 0
1:
beq a2, t2, 2f
lbu t0, 0(a0)
lbu t1, 0(a1)
addi a0, a0, 1
addi a1, a1, 1
bne t0, t1, 3f
addi t2, t2, 1
bnez t0, 1b
2:
li a0, 0
ret
3:
/*
* strncmp only needs to return (< 0, 0, > 0) values
* not necessarily -1, 0, +1
*/
sub a0, t0, t1
ret
/*
* Variant of strncmp using the ZBB extension if available
*/
#ifdef CONFIG_RISCV_ISA_ZBB
strncmp_zbb:
.option push
.option arch,+zbb
/*
* Returns
* a0 - comparison result, like strncmp
*
* Parameters
* a0 - string1
* a1 - string2
* a2 - number of characters to compare
*
* Clobbers
* t0, t1, t2, t3, t4, t5, t6
*/
or t2, a0, a1
li t5, -1
and t2, t2, SZREG-1
add t4, a0, a2
bnez t2, 3f
/* Adjust limit for fast-path. */
andi t6, t4, -SZREG
/* Main loop for aligned string. */
.p2align 3
1:
bge a0, t6, 3f
REG_L t0, 0(a0)
REG_L t1, 0(a1)
orc.b t3, t0
bne t3, t5, 2f
orc.b t3, t1
bne t3, t5, 2f
addi a0, a0, SZREG
addi a1, a1, SZREG
beq t0, t1, 1b
/*
* Words don't match, and no null byte in the first
* word. Get bytes in big-endian order and compare.
*/
#ifndef CONFIG_CPU_BIG_ENDIAN
rev8 t0, t0
rev8 t1, t1
#endif
/* Synthesize (t0 >= t1) ? 1 : -1 in a branchless sequence. */
sltu a0, t0, t1
neg a0, a0
ori a0, a0, 1
ret
2:
/*
* Found a null byte.
* If words don't match, fall back to simple loop.
*/
bne t0, t1, 3f
/* Otherwise, strings are equal. */
li a0, 0
ret
/* Simple loop for misaligned strings. */
.p2align 3
3:
bge a0, t4, 5f
lbu t0, 0(a0)
lbu t1, 0(a1)
addi a0, a0, 1
addi a1, a1, 1
bne t0, t1, 4f
bnez t0, 3b
4:
sub a0, t0, t1
ret
5:
li a0, 0
ret
.option pop
#endif
SYM_FUNC_END(strncmp)
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