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/* $NetBSD: memcmp.S,v 1.1 2014/08/10 05:47:35 matt Exp $ */
/*-
* Copyright (c) 2014 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Matt Thomas of 3am Software Foundry.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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/asm.h>
RCSID("$NetBSD: memcmp.S,v 1.1 2014/08/10 05:47:35 matt Exp $")
ENTRY(memcmp)
mov x9, x0
mov x10, x1
mov x0, xzr
cbz x2, .Lmemcmp_ret
#ifdef _KERNEL
cmp x2, #6
b.eq .Lmemcmp_6bytes
#endif
cmp x2, #7
b.ls .Lmemcmp_lessthan8
ands x3, x9, #7
b.eq .Lmemcmp_dword_loop
/*
* The two addresses have identical alignment but are not yet dword aligned.
*/
add x2, x2, x3 /* add unalignment to length */
sub x2, x2, #8 /* now subtract a dword */
sub x9, x9, x3 /* dword align src1 */
sub x10, x10, x3 /* adjust src2 */
lsl x3, x3, #3 /* convert bytes to bits */
ldr x4, [x9], #8 /* load dword from src1 */
ldr x6, [x10], #8 /* load dword from src2 */
#ifdef __AARCH64EB__
lsl x4, x4, x3 /* discard leading bytes from data1 */
lsl x6, x6, x3 /* discard leading bytes from data2 */
#else
lsr x4, x4, x3 /* discard leading bytes from data1 */
lsr x6, x6, x3 /* discard leading bytes from data2 */
#endif
subs x0, x4, x6 /* compare data */
#ifdef __AARCH64EL__
b.ne .Lmemcmp_last_compare /* difference. find it */
#else
b.eq .Lmemcmp_dword_loop /* no difference. go to loop */
rev x4, x4 /* byte swap data1 */
rev x6, x6 /* byte swap data2 */
b .Lmemcmp_last_compare /* go find the difference. */
#endif
.Lmemcmp_dword_loop:
subs x2, x2, #8
b.mi .Lmemcmp_finish_dword
ldr x4, [x9], #8
ldr x6, [x10], #8
subs x0, x4, x6
b.eq .Lmemcmp_dword_loop /* no difference. go to loop */
#ifdef __AARCH64EB__
rev x4, x4 /* byte swap data1 */
rev x6, x6 /* byte swap data2 */
#endif
b .Lmemcmp_last_compare /* go find the difference. */
.Lmemcmp_finish_dword:
/*
* we might have gotten here with nothing left. If so, just bail.
*/
tst x2, #7
b.eq .Lmemcmp_ret
/*
*
*/
tbz x2, #2, .Lmemcmp_finish_word
ldr w4, [x9], #4
ldr w6, [x10], #4
#ifdef __AARCH64EB__
lsl x4, x4, #32 /* move to MSW */
lsl x6, x6, #32 /* move to MSW */
#endif
.Lmemcmp_finish_word:
tbz x2, #1, .Lmemcmp_finish_hword
ldrh w5, [x9], #2
ldrh w7, [x10], #2
#ifdef __AARCH64EB__
orr x4, x4, x5, lsl #16
orr x6, x6, x7, lsl #16
#else
orr x4, x4, x5, lsl #32
orr x6, x6, x7, lsl #32
#endif
.Lmemcmp_finish_hword:
#ifdef __AARCH64EB__
rev x4, x4 /* byte swap data1 */
rev x6, x6 /* byte swap data1 */
#endif
tbz x2, #0, .Lmemcmp_last_compare
ldrb w5, [x9]
ldrb w7, [x10]
orr x4, x4, x5, lsl #48
orr x6, x6, x7, lsl #48
b .Lmemcmp_last_compare /* go find the difference. */
/*
* D
*/
.Lmemcmp_lessthan8:
sub x2, x2, #1
1: ldrb w4, [x9], #1
ldrb w5, [x10], #1
subs x2, x2, #1
ccmp x4, x5, #0, cs
b.eq 1b
sub x0, x4, x5
.Lmemcmp_ret:
ret
#ifdef _KERNEL
.Lmemcmp_6bytes:
ldr w4, [x9], #4
ldrh w5, [x9]
#if __AARCH64EB__
orr x4, x4, x5, lsl #48
rev x4, x4
#else
orr x4, x4, x5, lsl #32
#endif
ldr w6, [x10], #4
ldrh w7, [x10]
#if __AARCH64EB__
orr x6, x6, x7, lsl #48
rev x6, x6
#else
orr x6, x6, x7, lsl #32
#endif
#endif /* _KERNEL */
/*
* We have loaded the final bytes in x4 and x6 in LE format. Now we have
* to figure what the difference is (if any). First we subtract. Any bytes
* that are the same will be 0. So to find the first non-zero byte we byterev
* and then use clz to find that byte.
* We mask the location to get the start of the byte. We shift both
* data dwords left to remove the equal part. Then we shift right to discard
* the trailing bytes. Then we subtract and return.
*/
subs x0, x4, x6
b.eq .Lmemcmp_ret
.Lmemcmp_last_compare:
rev x1, x0 /* byte reverse */
clz x1, x1 /* find first non-zero byte */
bfi x1, xzr, #0, #3 /* make it byte aligned */
lsr x0, x0, x1 /* shift to LSB */
sxtb w0, w0 /* sign extend */
ret
END(memcmp)
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