; | |
; Copyright (c) 2013 - 2016, 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. | |
; | |
; Parameters and result. | |
#define src1 r0 | |
#define src2 r1 | |
#define limit r2 | |
#define result r0 | |
; Internal variables. | |
#define data1 r3 | |
#define data2 r4 | |
#define limit_wd r5 | |
#define diff r6 | |
#define tmp1 r7 | |
#define tmp2 r12 | |
#define pos r8 | |
#define mask r14 | |
EXPORT InternalMemCompareMem | |
THUMB | |
AREA CompareMem, CODE, READONLY | |
InternalMemCompareMem | |
push {r4-r8, lr} | |
eor tmp1, src1, src2 | |
tst tmp1, #3 | |
bne Lmisaligned4 | |
ands tmp1, src1, #3 | |
bne Lmutual_align | |
add limit_wd, limit, #3 | |
nop.w | |
lsr limit_wd, limit_wd, #2 | |
; Start of performance-critical section -- one 32B cache line. | |
Lloop_aligned | |
ldr data1, [src1], #4 | |
ldr data2, [src2], #4 | |
Lstart_realigned | |
subs limit_wd, limit_wd, #1 | |
eor diff, data1, data2 ; Non-zero if differences found. | |
cbnz diff, L0 | |
bne Lloop_aligned | |
; End of performance-critical section -- one 32B cache line. | |
; Not reached the limit, must have found a diff. | |
L0 | |
cbnz limit_wd, Lnot_limit | |
// Limit % 4 == 0 => all bytes significant. | |
ands limit, limit, #3 | |
beq Lnot_limit | |
lsl limit, limit, #3 // Bits -> bytes. | |
mov mask, #~0 | |
lsl mask, mask, limit | |
bic data1, data1, mask | |
bic data2, data2, mask | |
orr diff, diff, mask | |
Lnot_limit | |
rev diff, diff | |
rev data1, data1 | |
rev data2, data2 | |
; 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, #28 | |
sub result, data1, data2, lsr #28 | |
pop {r4-r8, pc} | |
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, #3 | |
bic src2, src2, #3 | |
add limit, limit, tmp1 ; Adjust the limit for the extra. | |
lsl tmp1, tmp1, #2 ; Bytes beyond alignment -> bits. | |
ldr data1, [src1], #4 | |
neg tmp1, tmp1 ; Bits to alignment -32. | |
ldr data2, [src2], #4 | |
mov tmp2, #~0 | |
; Little-endian. Early bytes are at LSB. | |
lsr tmp2, tmp2, tmp1 ; Shift (tmp1 & 31). | |
add limit_wd, limit, #3 | |
orr data1, data1, tmp2 | |
orr data2, data2, tmp2 | |
lsr limit_wd, limit_wd, #2 | |
b Lstart_realigned | |
Lmisaligned4 | |
sub limit, limit, #1 | |
L1 | |
// Perhaps we can do better than this. | |
ldrb data1, [src1], #1 | |
ldrb data2, [src2], #1 | |
subs limit, limit, #1 | |
it cs | |
cmpcs data1, data2 | |
beq L1 | |
sub result, data1, data2 | |
pop {r4-r8, pc} | |
END |