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/*
* Copyright (C) 2013 ARM Ltd.
* Copyright (C) 2013 Linaro.
*
* This code is based on glibc cortex strings work originally authored by Linaro
* and re-licensed under GPLv2 for the Linux kernel. The original code can
* be found @
*
* http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
* files/head:/src/aarch64/
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#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
ENTRY(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 ca not 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
ENDPIPROC(strcmp)
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