arch/arm64/lib/strncmp.S - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * Copyright (C) 2013 ARM Ltd.
  * Copyright (C) 2013 Linaro.
  *
  * This code is based on glibc cortex strings work originally authored by Linaro
  * be found @
  *
  * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
  * files/head:/src/aarch64/
  */

 #include <linux/linkage.h>
 #include <asm/assembler.h>

 /*
  * compare two strings
  *
  * Parameters:
  *  x0 - const string 1 pointer
  *  x1 - const string 2 pointer
  *  x2 - the maximal length to be compared
  * Returns:
  *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
  *     respectively, to be less than, to match, or be greater than s2.
  */

 #define REP8_01 0x0101010101010101
 #define REP8_7f 0x7f7f7f7f7f7f7f7f
 #define REP8_80 0x8080808080808080

 /* Parameters and result.  */
 src1		.req	x0
 src2		.req	x1
 limit		.req	x2
 result		.req	x0

 /* Internal variables.  */
 data1		.req	x3
 data1w		.req	w3
 data2		.req	x4
 data2w		.req	w4
 has_nul		.req	x5
 diff		.req	x6
 syndrome	.req	x7
 tmp1		.req	x8
 tmp2		.req	x9
 tmp3		.req	x10
 zeroones	.req	x11
 pos		.req	x12
 limit_wd	.req	x13
 mask		.req	x14
 endloop		.req	x15

 SYM_FUNC_START_WEAK_PI(strncmp)
 	cbz	limit, .Lret0
 	eor	tmp1, src1, src2
 	mov	zeroones, #REP8_01
 	tst	tmp1, #7
 	b.ne	.Lmisaligned8
 	ands	tmp1, src1, #7
 	b.ne	.Lmutual_align
 	/* Calculate the number of full and partial words -1.  */
 	/*
 	* when limit is mulitply of 8, if not sub 1,
 	* the judgement of last dword will wrong.
 	*/
 	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
 	lsr	limit_wd, limit_wd, #3  /* Convert to Dwords.  */

 	/*
 	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
 	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
 	* can be done in parallel across the entire word.
 	*/
 .Lloop_aligned:
 	ldr	data1, [src1], #8
 	ldr	data2, [src2], #8
 .Lstart_realigned:
 	subs	limit_wd, limit_wd, #1
 	sub	tmp1, data1, zeroones
 	orr	tmp2, data1, #REP8_7f
 	eor	diff, data1, data2  /* Non-zero if differences found.  */
 	csinv	endloop, diff, xzr, pl  /* Last Dword or differences.*/
 	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
 	ccmp	endloop, #0, #0, eq
 	b.eq	.Lloop_aligned

 	/*Not reached the limit, must have found the end or a diff.  */
 	tbz	limit_wd, #63, .Lnot_limit

 	/* Limit % 8 == 0 => all bytes significant.  */
 	ands	limit, limit, #7
 	b.eq	.Lnot_limit

 	lsl	limit, limit, #3    /* Bits -> bytes.  */
 	mov	mask, #~0
 CPU_BE( lsr	mask, mask, limit )
 CPU_LE( lsl	mask, mask, limit )
 	bic	data1, data1, mask
 	bic	data2, data2, mask

 	/* Make sure that the NUL byte is marked in the syndrome.  */
 	orr	has_nul, has_nul, mask

 .Lnot_limit:
 	orr	syndrome, diff, has_nul
 	b	.Lcal_cmpresult

 .Lmutual_align:
 	/*
 	* Sources are mutually aligned, but are not currently at an
 	* alignment boundary.  Round down the addresses and then mask off
 	* the bytes that precede the start point.
 	* We also need to adjust the limit calculations, but without
 	* overflowing if the limit is near ULONG_MAX.
 	*/
 	bic	src1, src1, #7
 	bic	src2, src2, #7
 	ldr	data1, [src1], #8
 	neg	tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
 	ldr	data2, [src2], #8
 	mov	tmp2, #~0
 	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
 	/* Big-endian.  Early bytes are at MSB.  */
 CPU_BE( lsl	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */
 	/* Little-endian.  Early bytes are at LSB.  */
 CPU_LE( lsr	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */

 	and	tmp3, limit_wd, #7
 	lsr	limit_wd, limit_wd, #3
 	/* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
 	add	limit, limit, tmp1
 	add	tmp3, tmp3, tmp1
 	orr	data1, data1, tmp2
 	orr	data2, data2, tmp2
 	add	limit_wd, limit_wd, tmp3, lsr #3
 	b	.Lstart_realigned

 /*when src1 offset is not equal to src2 offset...*/
 .Lmisaligned8:
 	cmp	limit, #8
 	b.lo	.Ltiny8proc /*limit < 8... */
 	/*
 	* Get the align offset length to compare per byte first.
 	* After this process, one string's address will be aligned.*/
 	and	tmp1, src1, #7
 	neg	tmp1, tmp1
 	add	tmp1, tmp1, #8
 	and	tmp2, src2, #7
 	neg	tmp2, tmp2
 	add	tmp2, tmp2, #8
 	subs	tmp3, tmp1, tmp2
 	csel	pos, tmp1, tmp2, hi /*Choose the maximum. */
 	/*
 	* Here, limit is not less than 8, so directly run .Ltinycmp
 	* without checking the limit.*/
 	sub	limit, limit, pos
 .Ltinycmp:
 	ldrb	data1w, [src1], #1
 	ldrb	data2w, [src2], #1
 	subs	pos, pos, #1
 	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
 	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
 	b.eq	.Ltinycmp
 	cbnz	pos, 1f /*find the null or unequal...*/
 	cmp	data1w, #1
 	ccmp	data1w, data2w, #0, cs
 	b.eq	.Lstart_align /*the last bytes are equal....*/
 1:
 	sub	result, data1, data2
 	ret

 .Lstart_align:
 	lsr	limit_wd, limit, #3
 	cbz	limit_wd, .Lremain8
 	/*process more leading bytes to make str1 aligned...*/
 	ands	xzr, src1, #7
 	b.eq	.Lrecal_offset
 	add	src1, src1, tmp3	/*tmp3 is positive in this branch.*/
 	add	src2, src2, tmp3
 	ldr	data1, [src1], #8
 	ldr	data2, [src2], #8

 	sub	limit, limit, tmp3
 	lsr	limit_wd, limit, #3
 	subs	limit_wd, limit_wd, #1

 	sub	tmp1, data1, zeroones
 	orr	tmp2, data1, #REP8_7f
 	eor	diff, data1, data2  /* Non-zero if differences found.  */
 	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
 	bics	has_nul, tmp1, tmp2
 	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
 	b.ne	.Lunequal_proc
 	/*How far is the current str2 from the alignment boundary...*/
 	and	tmp3, tmp3, #7
 .Lrecal_offset:
 	neg	pos, tmp3
 .Lloopcmp_proc:
 	/*
 	* Divide the eight bytes into two parts. First,backwards the src2
 	* to an alignment boundary,load eight bytes from the SRC2 alignment
 	* boundary,then compare with the relative bytes from SRC1.
 	* If all 8 bytes are equal,then start the second part's comparison.
 	* Otherwise finish the comparison.
 	* This special handle can garantee all the accesses are in the
 	* thread/task space in avoid to overrange access.
 	*/
 	ldr	data1, [src1,pos]
 	ldr	data2, [src2,pos]
 	sub	tmp1, data1, zeroones
 	orr	tmp2, data1, #REP8_7f
 	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
 	eor	diff, data1, data2  /* Non-zero if differences found.  */
 	csinv	endloop, diff, xzr, eq
 	cbnz	endloop, .Lunequal_proc

 	/*The second part process*/
 	ldr	data1, [src1], #8
 	ldr	data2, [src2], #8
 	subs	limit_wd, limit_wd, #1
 	sub	tmp1, data1, zeroones
 	orr	tmp2, data1, #REP8_7f
 	eor	diff, data1, data2  /* Non-zero if differences found.  */
 	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
 	bics	has_nul, tmp1, tmp2
 	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
 	b.eq	.Lloopcmp_proc

 .Lunequal_proc:
 	orr	syndrome, diff, has_nul
 	cbz	syndrome, .Lremain8
 .Lcal_cmpresult:
 	/*
 	* reversed the byte-order as big-endian,then CLZ can find the most
 	* significant zero bits.
 	*/
 CPU_LE( rev	syndrome, syndrome )
 CPU_LE( rev	data1, data1 )
 CPU_LE( rev	data2, data2 )
 	/*
 	* For big-endian we cannot use the trick with the syndrome value
 	* as carry-propagation can corrupt the upper bits if the trailing
 	* bytes in the string contain 0x01.
 	* However, if there is no NUL byte in the dword, we can generate
 	* the result directly.  We can't just subtract the bytes as the
 	* MSB might be significant.
 	*/
 CPU_BE( cbnz	has_nul, 1f )
 CPU_BE( cmp	data1, data2 )
 CPU_BE( cset	result, ne )
 CPU_BE( cneg	result, result, lo )
 CPU_BE( ret )
 CPU_BE( 1: )
 	/* Re-compute the NUL-byte detection, using a byte-reversed value.*/
 CPU_BE( rev	tmp3, data1 )
 CPU_BE( sub	tmp1, tmp3, zeroones )
 CPU_BE( orr	tmp2, tmp3, #REP8_7f )
 CPU_BE( bic	has_nul, tmp1, tmp2 )
 CPU_BE( rev	has_nul, has_nul )
 CPU_BE( orr	syndrome, diff, has_nul )
 	/*
 	* The MS-non-zero bit of the syndrome marks either the first bit
 	* that is different, or the top bit of the first zero byte.
 	* Shifting left now will bring the critical information into the
 	* top bits.
 	*/
 	clz	pos, syndrome
 	lsl	data1, data1, pos
 	lsl	data2, data2, pos
 	/*
 	* But we need to zero-extend (char is unsigned) the value and then
 	* perform a signed 32-bit subtraction.
 	*/
 	lsr	data1, data1, #56
 	sub	result, data1, data2, lsr #56
 	ret

 .Lremain8:
 	/* Limit % 8 == 0 => all bytes significant.  */
 	ands	limit, limit, #7
 	b.eq	.Lret0
 .Ltiny8proc:
 	ldrb	data1w, [src1], #1
 	ldrb	data2w, [src2], #1
 	subs	limit, limit, #1

 	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
 	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
 	b.eq	.Ltiny8proc
 	sub	result, data1, data2
 	ret

 .Lret0:
 	mov	result, #0
 	ret
 SYM_FUNC_END_PI(strncmp)
 EXPORT_SYMBOL_NOKASAN(strncmp)
	/* SPDX-License-Identifier: GPL-2.0-only */
	/*
	* Copyright (C) 2013 ARM Ltd.
	* Copyright (C) 2013 Linaro.
	*
	* This code is based on glibc cortex strings work originally authored by Linaro
	* be found @
	*
	* http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
	* files/head:/src/aarch64/
	*/

	#include <linux/linkage.h>
	#include <asm/assembler.h>

	/*
	* compare two strings
	*
	* Parameters:
	* x0 - const string 1 pointer
	* x1 - const string 2 pointer
	* x2 - the maximal length to be compared
	* Returns:
	* x0 - an integer less than, equal to, or greater than zero if s1 is found,
	* respectively, to be less than, to match, or be greater than s2.
	*/

	#define REP8_01 0x0101010101010101
	#define REP8_7f 0x7f7f7f7f7f7f7f7f
	#define REP8_80 0x8080808080808080

	/* Parameters and result. */
	src1 .req x0
	src2 .req x1
	limit .req x2
	result .req x0

	/* Internal variables. */
	data1 .req x3
	data1w .req w3
	data2 .req x4
	data2w .req w4
	has_nul .req x5
	diff .req x6
	syndrome .req x7
	tmp1 .req x8
	tmp2 .req x9
	tmp3 .req x10
	zeroones .req x11
	pos .req x12
	limit_wd .req x13
	mask .req x14
	endloop .req x15

	SYM_FUNC_START_WEAK_PI(strncmp)
	cbz limit, .Lret0
	eor tmp1, src1, src2
	mov zeroones, #REP8_01
	tst tmp1, #7
	b.ne .Lmisaligned8
	ands tmp1, src1, #7
	b.ne .Lmutual_align
	/* Calculate the number of full and partial words -1. */
	/*
	* when limit is mulitply of 8, if not sub 1,
	* the judgement of last dword will wrong.
	*/
	sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
	lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */

	/*
	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
	* (=> (X - 1) & ~(X \| 0x7f)) is non-zero iff a byte is zero, and
	* can be done in parallel across the entire word.
	*/
	.Lloop_aligned:
	ldr data1, [src1], #8
	ldr data2, [src2], #8
	.Lstart_realigned:
	subs limit_wd, limit_wd, #1
	sub tmp1, data1, zeroones
	orr tmp2, data1, #REP8_7f
	eor diff, data1, data2 /* Non-zero if differences found. */
	csinv endloop, diff, xzr, pl /* Last Dword or differences.*/
	bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
	ccmp endloop, #0, #0, eq
	b.eq .Lloop_aligned

	/Not reached the limit, must have found the end or a diff. /
	tbz limit_wd, #63, .Lnot_limit

	/* Limit % 8 == 0 => all bytes significant. */
	ands limit, limit, #7
	b.eq .Lnot_limit

	lsl limit, limit, #3 /* Bits -> bytes. */
	mov mask, #~0
	CPU_BE( lsr mask, mask, limit )
	CPU_LE( lsl mask, mask, limit )
	bic data1, data1, mask
	bic data2, data2, mask

	/* Make sure that the NUL byte is marked in the syndrome. */
	orr has_nul, has_nul, mask

	.Lnot_limit:
	orr syndrome, diff, has_nul
	b .Lcal_cmpresult

	.Lmutual_align:
	/*
	* Sources are mutually aligned, but are not currently at an
	* alignment boundary. Round down the addresses and then mask off
	* the bytes that precede the start point.
	* We also need to adjust the limit calculations, but without
	* overflowing if the limit is near ULONG_MAX.
	*/
	bic src1, src1, #7
	bic src2, src2, #7
	ldr data1, [src1], #8
	neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */
	ldr data2, [src2], #8
	mov tmp2, #~0
	sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
	/* Big-endian. Early bytes are at MSB. */
	CPU_BE( lsl tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */
	/* Little-endian. Early bytes are at LSB. */
	CPU_LE( lsr tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */

	and tmp3, limit_wd, #7
	lsr limit_wd, limit_wd, #3
	/* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
	add limit, limit, tmp1
	add tmp3, tmp3, tmp1
	orr data1, data1, tmp2
	orr data2, data2, tmp2
	add limit_wd, limit_wd, tmp3, lsr #3
	b .Lstart_realigned

	/when src1 offset is not equal to src2 offset.../
	.Lmisaligned8:
	cmp limit, #8
	b.lo .Ltiny8proc /limit < 8... /
	/*
	* Get the align offset length to compare per byte first.
	* After this process, one string's address will be aligned.*/
	and tmp1, src1, #7
	neg tmp1, tmp1
	add tmp1, tmp1, #8
	and tmp2, src2, #7
	neg tmp2, tmp2
	add tmp2, tmp2, #8
	subs tmp3, tmp1, tmp2
	csel pos, tmp1, tmp2, hi /Choose the maximum. /
	/*
	* Here, limit is not less than 8, so directly run .Ltinycmp
	* without checking the limit.*/
	sub limit, limit, pos
	.Ltinycmp:
	ldrb data1w, [src1], #1
	ldrb data2w, [src2], #1
	subs pos, pos, #1
	ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
	ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
	b.eq .Ltinycmp
	cbnz pos, 1f /find the null or unequal.../
	cmp data1w, #1
	ccmp data1w, data2w, #0, cs
	b.eq .Lstart_align /the last bytes are equal..../
	1:
	sub result, data1, data2
	ret

	.Lstart_align:
	lsr limit_wd, limit, #3
	cbz limit_wd, .Lremain8
	/process more leading bytes to make str1 aligned.../
	ands xzr, src1, #7
	b.eq .Lrecal_offset
	add src1, src1, tmp3 /tmp3 is positive in this branch./
	add src2, src2, tmp3
	ldr data1, [src1], #8
	ldr data2, [src2], #8

	sub limit, limit, tmp3
	lsr limit_wd, limit, #3
	subs limit_wd, limit_wd, #1

	sub tmp1, data1, zeroones
	orr tmp2, data1, #REP8_7f
	eor diff, data1, data2 /* Non-zero if differences found. */
	csinv endloop, diff, xzr, ne/if limit_wd is 0,will finish the cmp/
	bics has_nul, tmp1, tmp2
	ccmp endloop, #0, #0, eq /has_null is ZERO: no null byte/
	b.ne .Lunequal_proc
	/How far is the current str2 from the alignment boundary.../
	and tmp3, tmp3, #7
	.Lrecal_offset:
	neg pos, tmp3
	.Lloopcmp_proc:
	/*
	* Divide the eight bytes into two parts. First,backwards the src2
	* to an alignment boundary,load eight bytes from the SRC2 alignment
	* boundary,then compare with the relative bytes from SRC1.
	* If all 8 bytes are equal,then start the second part's comparison.
	* Otherwise finish the comparison.
	* This special handle can garantee all the accesses are in the
	* thread/task space in avoid to overrange access.
	*/
	ldr data1, [src1,pos]
	ldr data2, [src2,pos]
	sub tmp1, data1, zeroones
	orr tmp2, data1, #REP8_7f
	bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
	eor diff, data1, data2 /* Non-zero if differences found. */
	csinv endloop, diff, xzr, eq
	cbnz endloop, .Lunequal_proc

	/The second part process/
	ldr data1, [src1], #8
	ldr data2, [src2], #8
	subs limit_wd, limit_wd, #1
	sub tmp1, data1, zeroones
	orr tmp2, data1, #REP8_7f
	eor diff, data1, data2 /* Non-zero if differences found. */
	csinv endloop, diff, xzr, ne/if limit_wd is 0,will finish the cmp/
	bics has_nul, tmp1, tmp2
	ccmp endloop, #0, #0, eq /has_null is ZERO: no null byte/
	b.eq .Lloopcmp_proc

	.Lunequal_proc:
	orr syndrome, diff, has_nul
	cbz syndrome, .Lremain8
	.Lcal_cmpresult:
	/*
	* reversed the byte-order as big-endian,then CLZ can find the most
	* significant zero bits.
	*/
	CPU_LE( rev syndrome, syndrome )
	CPU_LE( rev data1, data1 )
	CPU_LE( rev data2, data2 )
	/*
	* For big-endian we cannot use the trick with the syndrome value
	* as carry-propagation can corrupt the upper bits if the trailing
	* bytes in the string contain 0x01.
	* However, if there is no NUL byte in the dword, we can generate
	* the result directly. We can't just subtract the bytes as the
	* MSB might be significant.
	*/
	CPU_BE( cbnz has_nul, 1f )
	CPU_BE( cmp data1, data2 )
	CPU_BE( cset result, ne )
	CPU_BE( cneg result, result, lo )
	CPU_BE( ret )
	CPU_BE( 1: )
	/* Re-compute the NUL-byte detection, using a byte-reversed value.*/
	CPU_BE( rev tmp3, data1 )
	CPU_BE( sub tmp1, tmp3, zeroones )
	CPU_BE( orr tmp2, tmp3, #REP8_7f )
	CPU_BE( bic has_nul, tmp1, tmp2 )
	CPU_BE( rev has_nul, has_nul )
	CPU_BE( orr syndrome, diff, has_nul )
	/*
	* The MS-non-zero bit of the syndrome marks either the first bit
	* that is different, or the top bit of the first zero byte.
	* Shifting left now will bring the critical information into the
	* top bits.
	*/
	clz pos, syndrome
	lsl data1, data1, pos
	lsl data2, data2, pos
	/*
	* But we need to zero-extend (char is unsigned) the value and then
	* perform a signed 32-bit subtraction.
	*/
	lsr data1, data1, #56
	sub result, data1, data2, lsr #56
	ret

	.Lremain8:
	/* Limit % 8 == 0 => all bytes significant. */
	ands limit, limit, #7
	b.eq .Lret0
	.Ltiny8proc:
	ldrb data1w, [src1], #1
	ldrb data2w, [src2], #1
	subs limit, limit, #1

	ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
	ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
	b.eq .Ltiny8proc
	sub result, data1, data2
	ret

	.Lret0:
	mov result, #0
	ret
	SYM_FUNC_END_PI(strncmp)
	EXPORT_SYMBOL_NOKASAN(strncmp)