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/* memcmp - compare memory
Copyright (C) 2013-2014 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* Assumptions:
*
* ARMv8-a, AArch64
*/
/* Parameters and result. */
#define src1 x0
#define src2 x1
#define limit x2
#define result x0
/* Internal variables. */
#define data1 x3
#define data1w w3
#define data2 x4
#define data2w w4
#define has_nul x5
#define diff x6
#define endloop x7
#define tmp1 x8
#define tmp2 x9
#define tmp3 x10
#define pos x11
#define limit_wd x12
#define mask x13
ENTRY_ALIGN (memcmp, 6)
cbz limit, L(ret0)
eor tmp1, src1, src2
tst tmp1, #7
b.ne L(misaligned8)
ands tmp1, src1, #7
b.ne L(mutual_align)
add limit_wd, limit, #7
lsr limit_wd, limit_wd, #3
/* Start of performance-critical section -- one 64B cache line. */
L(loop_aligned):
ldr data1, [src1], #8
ldr data2, [src2], #8
L(start_realigned):
subs limit_wd, limit_wd, #1
eor diff, data1, data2 /* Non-zero if differences found. */
csinv endloop, diff, xzr, ne /* Last Dword or differences. */
cbz endloop, L(loop_aligned)
/* End of performance-critical section -- one 64B cache line. */
/* Not reached the limit, must have found a diff. */
cbnz limit_wd, L(not_limit)
/* Limit % 8 == 0 => all bytes significant. */
ands limit, limit, #7
b.eq L(not_limit)
lsl limit, limit, #3 /* Bits -> bytes. */
mov mask, #~0
#ifdef __AARCH64EB__
lsr mask, mask, limit
#else
lsl mask, mask, limit
#endif
bic data1, data1, mask
bic data2, data2, mask
orr diff, diff, mask
L(not_limit):
#ifndef __AARCH64EB__
rev diff, diff
rev data1, data1
rev data2, data2
#endif
/* The MS-non-zero bit of DIFF marks either the first bit
that is different, or the end of the significant data.
Shifting left now will bring the critical information into the
top bits. */
clz pos, diff
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
L(mutual_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. */
bic src1, src1, #7
bic src2, src2, #7
add limit, limit, tmp1 /* Adjust the limit for the extra. */
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
#ifdef __AARCH64EB__
/* Big-endian. Early bytes are at MSB. */
lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
#else
/* Little-endian. Early bytes are at LSB. */
lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
#endif
add limit_wd, limit, #7
orr data1, data1, tmp2
orr data2, data2, tmp2
lsr limit_wd, limit_wd, #3
b L(start_realigned)
L(ret0):
mov result, #0
RET
.p2align 6
L(misaligned8):
sub limit, limit, #1
1:
/* Perhaps we can do better than this. */
ldrb data1w, [src1], #1
ldrb data2w, [src2], #1
subs limit, limit, #1
ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
b.eq 1b
sub result, data1, data2
RET
END (memcmp)
#undef bcmp
weak_alias (memcmp, bcmp)
libc_hidden_builtin_def (memcmp)
|
