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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Taken from Linux arch/riscv/lib/strlen.S
*/
#include <linux/linkage.h>
#include <asm/asm.h>
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
# define CZ ctz
# define SHIFT srl
#else
# define CZ clz
# define SHIFT sll
#endif
ENTRY(__strlen)
WEAK(strlen)
.option push
.option arch,+zbb
/*
* Returns
* a0 - string length
*
* Parameters
* a0 - String to measure
*
* Clobbers
* t0, t1, t2, t3
*/
/* Number of irrelevant bytes in the first word. */
andi t2, a0, SZREG-1
/* Align pointer. */
andi t0, a0, -SZREG
li t3, SZREG
sub t3, t3, t2
slli t2, t2, 3
/* Get the first word. */
REG_L t1, 0(t0)
/*
* Shift away the partial data we loaded to remove the irrelevant bytes
* preceding the string with the effect of adding NUL bytes at the
* end of the string's first word.
*/
SHIFT t1, t1, t2
/* Convert non-NUL into 0xff and NUL into 0x00. */
orc.b t1, t1
/* Convert non-NUL into 0x00 and NUL into 0xff. */
not t1, t1
/*
* Search for the first set bit (corresponding to a NUL byte in the
* original chunk).
*/
CZ t1, t1
/*
* The first chunk is special: compare against the number
* of valid bytes in this chunk.
*/
srli a0, t1, 3
bgtu t3, a0, 2f
/* Prepare for the word comparison loop. */
addi t2, t0, SZREG
li t3, -1
/*
* Our critical loop is 4 instructions and processes data in
* 4 byte or 8 byte chunks.
*/
.p2align 3
1:
REG_L t1, SZREG(t0)
addi t0, t0, SZREG
orc.b t1, t1
beq t1, t3, 1b
not t1, t1
CZ t1, t1
srli t1, t1, 3
/* Get number of processed bytes. */
sub t2, t0, t2
/* Add number of characters in the first word. */
add a0, a0, t2
/* Add number of characters in the last word. */
add a0, a0, t1
2:
ret
.option pop
END(__strlen)
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