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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
.text
.thumb
.syntax unified
.align 5
.type ASM_PFX(InternalMemCompareMem), %function
ASM_GLOBAL ASM_PFX(InternalMemCompareMem)
ASM_PFX(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, 0f
bne .Lloop_aligned
// End of performance-critical section -- one 32B cache line.
// Not reached the limit, must have found a diff.
0: 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, #3 // Bytes beyond alignment -> bits.
ldr data1, [src1], #4
rsb tmp1, tmp1, #32 // 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
1:
// Perhaps we can do better than this.
ldrb data1, [src1], #1
ldrb data2, [src2], #1
subs limit, limit, #1
it cs
cmpcs.n data1, data2
beq 1b
sub result, data1, data2
pop {r4-r8, pc}
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