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|
;
; Copyright (c) 2013 - 2016, Linaro Limited
; All rights reserved.
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
; 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
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