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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/riscv/lib/strlen.S
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/* SPDX-License-Identifier: GPL-2.0-only */

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#include <linux/linkage.h>

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#include <asm/asm.h>

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#include <asm/alternative-macros.h>

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#include <asm/hwcap.h>

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/* int strlen(const char *s) */

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SYM_FUNC_START(strlen)

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	__ALTERNATIVE_CFG("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB,

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		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))

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	/*

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	 * Returns

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	 *   a0 - string length

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	 *

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	 * Parameters

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	 *   a0 - String to measure

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	 *

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	 * Clobbers:

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	 *   t0, t1

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	 */

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	mv	t1, a0

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1:

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	lbu	t0, 0(t1)

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	beqz	t0, 2f

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	addi	t1, t1, 1

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	j	1b

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2:

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	sub	a0, t1, a0

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	ret

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/*

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 * Variant of strlen using the ZBB extension if available

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 */

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#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)

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strlen_zbb:

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#ifdef CONFIG_CPU_BIG_ENDIAN

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# define CZ	clz

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# define SHIFT	sll

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#else

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# define CZ	ctz

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# define SHIFT	srl

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#endif

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.option push

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.option arch,+zbb

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	/*

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	 * Returns

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	 *   a0 - string length

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	 *

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	 * Parameters

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	 *   a0 - String to measure

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	 *

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	 * Clobbers

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	 *   t0, t1, t2, t3

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	 */

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	/* Number of irrelevant bytes in the first word. */

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	andi	t2, a0, SZREG-1

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	/* Align pointer. */

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	andi	t0, a0, -SZREG

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	li	t3, SZREG

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	sub	t3, t3, t2

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	slli	t2, t2, 3

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	/* Get the first word.  */

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	REG_L	t1, 0(t0)

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	/*

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	 * Shift away the partial data we loaded to remove the irrelevant bytes

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	 * preceding the string with the effect of adding NUL bytes at the

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	 * end of the string's first word.

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	 */

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	SHIFT	t1, t1, t2

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	/* Convert non-NUL into 0xff and NUL into 0x00. */

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	orc.b	t1, t1

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	/* Convert non-NUL into 0x00 and NUL into 0xff. */

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	not	t1, t1

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	/*

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	 * Search for the first set bit (corresponding to a NUL byte in the

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	 * original chunk).

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	 */

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	CZ	t1, t1

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	/*

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	 * The first chunk is special: compare against the number

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	 * of valid bytes in this chunk.

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	 */

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	srli	a0, t1, 3

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	bgtu	t3, a0, 2f

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	/* Prepare for the word comparison loop. */

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	addi	t2, t0, SZREG

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	li	t3, -1

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	/*

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	 * Our critical loop is 4 instructions and processes data in

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	 * 4 byte or 8 byte chunks.

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	 */

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	.p2align 3

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1:

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	REG_L	t1, SZREG(t0)

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	addi	t0, t0, SZREG

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	orc.b	t1, t1

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	beq	t1, t3, 1b

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	not	t1, t1

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	CZ	t1, t1

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	srli	t1, t1, 3

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	/* Get number of processed bytes. */

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	sub	t2, t0, t2

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	/* Add number of characters in the first word.  */

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	add	a0, a0, t2

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	/* Add number of characters in the last word.  */

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	add	a0, a0, t1

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2:

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	ret

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.option pop

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#endif

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SYM_FUNC_END(strlen)

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SYM_FUNC_ALIAS(__pi_strlen, strlen)

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EXPORT_SYMBOL(strlen)

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