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/* 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
* 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
result .req x0
/* Internal variables. */
data1 .req x2
data1w .req w2
data2 .req x3
data2w .req w3
has_nul .req x4
diff .req x5
syndrome .req x6
tmp1 .req x7
tmp2 .req x8
tmp3 .req x9
zeroones .req x10
pos .req x11
SYM_FUNC_START_WEAK_PI(strcmp)
eor tmp1, src1, src2
mov zeroones, #REP8_01
tst tmp1, #7
b.ne .Lmisaligned8
ands tmp1, src1, #7
b.ne .Lmutual_align
/*
* 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:
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
eor diff, data1, data2 /* Non-zero if differences found. */
bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
orr syndrome, diff, has_nul
cbz syndrome, .Lloop_aligned
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 preceed the start point.
*/
bic src1, src1, #7
bic src2, src2, #7
lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
ldr data1, [src1], #8
neg tmp1, tmp1 /* Bits to alignment -64. */
ldr data2, [src2], #8
mov tmp2, #~0
/* Big-endian. Early bytes are at MSB. */
CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
/* Little-endian. Early bytes are at LSB. */
CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
orr data1, data1, tmp2
orr data2, data2, tmp2
b .Lstart_realigned
.Lmisaligned8:
/*
* 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. */
.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:
ands xzr, src1, #7
b.eq .Lrecal_offset
/*process more leading bytes to make str1 aligned...*/
add src1, src1, tmp3
add src2, src2, tmp3
/*load 8 bytes from aligned str1 and non-aligned str2..*/
ldr data1, [src1], #8
ldr data2, [src2], #8
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
bic has_nul, tmp1, tmp2
eor diff, data1, data2 /* Non-zero if differences found. */
orr syndrome, diff, has_nul
cbnz syndrome, .Lcal_cmpresult
/*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
bic has_nul, tmp1, tmp2
eor diff, data1, data2 /* Non-zero if differences found. */
orr syndrome, diff, has_nul
cbnz syndrome, .Lcal_cmpresult
/*The second part process*/
ldr data1, [src1], #8
ldr data2, [src2], #8
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
bic has_nul, tmp1, tmp2
eor diff, data1, data2 /* Non-zero if differences found. */
orr syndrome, diff, has_nul
cbz syndrome, .Lloopcmp_proc
.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 cannot 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 )
clz pos, syndrome
/*
* 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.
*/
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
SYM_FUNC_END_PI(strcmp)
EXPORT_SYMBOL_NOKASAN(strcmp)
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