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/* memcmp - compare memory
Copyright (c) 2013, Linaro Limited
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of the Linaro nor the
names of its contributors may be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
#if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
/* See memcmp-stub.c */
#else
/* Assumptions:
*
* ARMv8-a, AArch64
*/
.macro def_fn f p2align=0
.text
.p2align \p2align
.global \f
.type \f, %function
\f:
.endm
/* 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
def_fn memcmp p2align=6
cbz limit, .Lret0
eor tmp1, src1, src2
tst tmp1, #7
b.ne .Lmisaligned8
ands tmp1, src1, #7
b.ne .Lmutual_align
add limit_wd, limit, #7
lsr limit_wd, limit_wd, #3
/* Start of performance-critical section -- one 64B cache line. */
.Lloop_aligned:
ldr data1, [src1], #8
ldr data2, [src2], #8
.Lstart_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, .Lloop_aligned
/* End of performance-critical section -- one 64B cache line. */
/* Not reached the limit, must have found a diff. */
cbnz limit_wd, .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
#ifdef __AARCH64EB__
lsr mask, mask, limit
#else
lsl mask, mask, limit
#endif
bic data1, data1, mask
bic data2, data2, mask
orr diff, diff, mask
.Lnot_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
.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. */
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 .Lstart_realigned
.Lret0:
mov result, #0
ret
.p2align 6
.Lmisaligned8:
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
.size memcmp, . - memcmp
#endif
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