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