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/*
* Copyright (C) 2008 The Android Open Source Project
* 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.
*
* 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 OWNER 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.
*/
.text
.global __memcmp16
.type __memcmp16, %function
.align 4
/*
* Optimized memcmp16() for ARM9.
* This would not be optimal on XScale or ARM11, where more prefetching
* and use of PLD will be needed.
* The 2 major optimzations here are
* (1) The main loop compares 16 bytes at a time
* (2) The loads are scheduled in a way they won't stall
*/
__memcmp16:
pld [r0, #0]
pld [r1, #0]
/* take of the case where length is nul or the buffers are the same */
cmp r0, r1
cmpne r2, #0
moveq r0, #0
bxeq lr
/* since r0 hold the result, move the first source
* pointer somewhere else
*/
mov r3, r0
/* make sure we have at least 12 words, this simplify things below
* and avoid some overhead for small blocks
*/
cmp r2, #12
bpl 0f
/* small blocks (less then 12 words) */
pld [r0, #32]
pld [r1, #32]
1: ldrh r0, [r3], #2
ldrh ip, [r1], #2
subs r0, r0, ip
bxne lr
subs r2, r2, #1
bne 1b
bx lr
/* save registers */
0: stmfd sp!, {r4, lr}
/* align first pointer to word boundary */
tst r3, #2
beq 0f
ldrh r0, [r3], #2
ldrh ip, [r1], #2
sub r2, r2, #1
subs r0, r0, ip
/* restore registers and return */
ldmnefd sp!, {r4, lr}
bxne lr
0: /* here the first pointer is aligned, and we have at least 3 words
* to process.
*/
/* see if the pointers are congruent */
eor r0, r3, r1
ands r0, r0, #2
bne 5f
/* congruent case, 16 half-words per iteration
* We need to make sure there are at least 16+2 words left
* because we effectively read ahead one long word, and we could
* read past the buffer (and segfault) if we're not careful.
*/
ldr ip, [r1]
subs r2, r2, #(16 + 2)
bmi 1f
0:
pld [r3, #64]
pld [r1, #64]
ldr r0, [r3], #4
ldr lr, [r1, #4]!
eors r0, r0, ip
ldreq r0, [r3], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r3], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r3], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r3], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r3], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r3], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r3], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
bne 2f
subs r2, r2, #16
bhs 0b
/* do we have at least 2 words left? */
1: adds r2, r2, #(16 - 2 + 2)
bmi 4f
/* finish off 2 words at a time */
3: ldr r0, [r3], #4
ldr ip, [r1], #4
eors r0, r0, ip
bne 2f
subs r2, r2, #2
bhs 3b
/* are we done? */
4: adds r2, r2, #2
bne 8f
/* restore registers and return */
mov r0, #0
ldmfd sp!, {r4, lr}
bx lr
2: /* the last 2 words are different, restart them */
ldrh r0, [r3, #-4]
ldrh ip, [r1, #-4]
subs r0, r0, ip
ldreqh r0, [r3, #-2]
ldreqh ip, [r1, #-2]
subeqs r0, r0, ip
/* restore registers and return */
ldmfd sp!, {r4, lr}
bx lr
/* process the last few words */
8: ldrh r0, [r3], #2
ldrh ip, [r1], #2
subs r0, r0, ip
bne 9f
subs r2, r2, #1
bne 8b
9: /* restore registers and return */
ldmfd sp!, {r4, lr}
bx lr
5: /*************** non-congruent case ***************/
/* align the unaligned pointer */
bic r1, r1, #3
ldr lr, [r1], #4
sub r2, r2, #8
6:
pld [r3, #64]
pld [r1, #64]
mov ip, lr, lsr #16
ldr lr, [r1], #4
ldr r0, [r3], #4
orr ip, ip, lr, lsl #16
eors r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r3], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r3], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r3], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
bne 7f
subs r2, r2, #8
bhs 6b
sub r1, r1, #2
/* are we done? */
adds r2, r2, #8
moveq r0, #0
beq 9b
/* finish off the remaining bytes */
b 8b
7: /* fix up the 2 pointers and fallthrough... */
sub r1, r1, #2
b 2b
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