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//
// 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.
//
// 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 diff x6
#define endloop x7
#define tmp1 x8
#define tmp2 x9
#define pos x11
#define limit_wd x12
#define mask x13
.p2align 6
ASM_GLOBAL ASM_PFX(InternalMemCompareMem)
ASM_PFX(InternalMemCompareMem):
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
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, #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
// Little-endian. Early bytes are at LSB.
lsr tmp2, tmp2, tmp1 // Shift (tmp1 & 63).
add limit_wd, limit, #7
orr data1, data1, tmp2
orr data2, data2, tmp2
lsr limit_wd, limit_wd, #3
b .Lstart_realigned
.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
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