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Diffstat (limited to 'libc/arch-arm/bionic/memcmp.S')
| -rw-r--r-- | libc/arch-arm/bionic/memcmp.S | 285 |
1 files changed, 285 insertions, 0 deletions
diff --git a/libc/arch-arm/bionic/memcmp.S b/libc/arch-arm/bionic/memcmp.S new file mode 100644 index 0000000..f45b56b --- /dev/null +++ b/libc/arch-arm/bionic/memcmp.S @@ -0,0 +1,285 @@ +/* + * 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. + */ + +#include <machine/cpu-features.h> + + .text + + .global memcmp + .type memcmp, %function + .align 4 + +/* + * Optimized memcmp() 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 + */ + +memcmp: + PLD (r0, #0) + PLD (r1, #0) + + /* take of the case where length is 0 or the buffers are the same */ + cmp r0, r1 + cmpne r2, #0 + moveq r0, #0 + bxeq lr + + /* save registers */ + stmfd sp!, {r4, lr} + + PLD (r0, #32) + PLD (r1, #32) + + /* since r0 hold the result, move the first source + * pointer somewhere else + */ + + mov r4, r0 + + /* make sure we have at least 8+4 bytes, this simplify things below + * and avoid some overhead for small blocks + */ + cmp r2, #(8+4) + bmi 8f + + /* align first pointer to word boundary + * offset = -src & 3 + */ + rsb r3, r4, #0 + ands r3, r3, #3 + beq 0f + + /* align first pointer */ + sub r2, r2, r3 +1: ldrb r0, [r4], #1 + ldrb ip, [r1], #1 + subs r0, r0, ip + bne 9f + subs r3, r3, #1 + bne 1b + + +0: /* here the first pointer is aligned, and we have at least 4 bytes + * to process. + */ + + /* see if the pointers are congruent */ + eor r0, r4, r1 + ands r0, r0, #3 + bne 5f + + /* congruent case, 32 bytes per iteration + * We need to make sure there are at least 32+4 bytes left + * because we effectively read ahead one word, and we could + * read past the buffer (and segfault) if we're not careful. + */ + + ldr ip, [r1] + subs r2, r2, #(32 + 4) + bmi 1f + +0: PLD (r4, #64) + PLD (r1, #64) + ldr r0, [r4], #4 + ldr lr, [r1, #4]! + eors r0, r0, ip + ldreq r0, [r4], #4 + ldreq ip, [r1, #4]! + eoreqs r0, r0, lr + ldreq r0, [r4], #4 + ldreq lr, [r1, #4]! + eoreqs r0, r0, ip + ldreq r0, [r4], #4 + ldreq ip, [r1, #4]! + eoreqs r0, r0, lr + ldreq r0, [r4], #4 + ldreq lr, [r1, #4]! + eoreqs r0, r0, ip + ldreq r0, [r4], #4 + ldreq ip, [r1, #4]! + eoreqs r0, r0, lr + ldreq r0, [r4], #4 + ldreq lr, [r1, #4]! + eoreqs r0, r0, ip + ldreq r0, [r4], #4 + ldreq ip, [r1, #4]! + eoreqs r0, r0, lr + bne 2f + subs r2, r2, #32 + bhs 0b + + /* do we have at least 4 bytes left? */ +1: adds r2, r2, #(32 - 4 + 4) + bmi 4f + + /* finish off 4 bytes at a time */ +3: ldr r0, [r4], #4 + ldr ip, [r1], #4 + eors r0, r0, ip + bne 2f + subs r2, r2, #4 + bhs 3b + + /* are we done? */ +4: adds r2, r2, #4 + moveq r0, #0 + beq 9f + + /* finish off the remaining bytes */ + b 8f + +2: /* the last 4 bytes are different, restart them */ + sub r4, r4, #4 + sub r1, r1, #4 + mov r2, #4 + + /* process the last few bytes */ +8: ldrb r0, [r4], #1 + ldrb ip, [r1], #1 + // stall + 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 ***************/ + and r0, r1, #3 + cmp r0, #2 + bne 4f + + /* here, offset is 2 (16-bits aligned, special cased) */ + + /* make sure we have at least 16 bytes to process */ + subs r2, r2, #16 + addmi r2, r2, #16 + bmi 8b + + /* align the unaligned pointer */ + bic r1, r1, #3 + ldr lr, [r1], #4 + +6: PLD (r1, #64) + PLD (r4, #64) + mov ip, lr, lsr #16 + ldr lr, [r1], #4 + ldr r0, [r4], #4 + orr ip, ip, lr, lsl #16 + eors r0, r0, ip + moveq ip, lr, lsr #16 + ldreq lr, [r1], #4 + ldreq r0, [r4], #4 + orreq ip, ip, lr, lsl #16 + eoreqs r0, r0, ip + moveq ip, lr, lsr #16 + ldreq lr, [r1], #4 + ldreq r0, [r4], #4 + orreq ip, ip, lr, lsl #16 + eoreqs r0, r0, ip + moveq ip, lr, lsr #16 + ldreq lr, [r1], #4 + ldreq r0, [r4], #4 + orreq ip, ip, lr, lsl #16 + eoreqs r0, r0, ip + bne 7f + subs r2, r2, #16 + bhs 6b + sub r1, r1, #2 + /* are we done? */ + adds r2, r2, #16 + moveq r0, #0 + beq 9b + /* finish off the remaining bytes */ + b 8b + +7: /* fix up the 2 pointers and fallthrough... */ + sub r1, r1, #(4+2) + sub r4, r4, #4 + mov r2, #4 + b 8b + + +4: /*************** offset is 1 or 3 (less optimized) ***************/ + + stmfd sp!, {r5, r6, r7} + + // r5 = rhs + // r6 = lhs + // r7 = scratch + + mov r5, r0, lsl #3 /* r5 = right shift */ + rsb r6, r5, #32 /* r6 = left shift */ + + /* align the unaligned pointer */ + bic r1, r1, #3 + ldr r7, [r1], #4 + sub r2, r2, #8 + +6: mov ip, r7, lsr r5 + ldr r7, [r1], #4 + ldr r0, [r4], #4 + orr ip, ip, r7, lsl r6 + eors r0, r0, ip + moveq ip, r7, lsr r5 + ldreq r7, [r1], #4 + ldreq r0, [r4], #4 + orreq ip, ip, r7, lsl r6 + eoreqs r0, r0, ip + bne 7f + subs r2, r2, #8 + bhs 6b + + sub r1, r1, r6, lsr #3 + ldmfd sp!, {r5, r6, r7} + + /* 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, #4 + sub r1, r1, r6, lsr #3 + sub r4, r4, #4 + mov r2, #4 + ldmfd sp!, {r5, r6, r7} + b 8b |