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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
|
|
