/*- * Copyright (c) 2013 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: strchr_arm.S,v 1.8 2013/08/19 17:50:04 matt Exp $") #if defined(__thumb__) && !defined(_ARM_ARCH_T2) #error Only Thumb2 or ARM supported #endif #ifdef __ARMEL__ #define BYTE0 0x000000ff #define BYTE1 0x0000ff00 #define BYTE2 0x00ff0000 #define BYTE3 0xff000000 #define lshi lsl #define lshis lsls #else #define BYTE0 0xff000000 #define BYTE1 0x00ff0000 #define BYTE2 0x0000ff00 #define BYTE3 0x000000ff #define lshi lsr #define lshis lsrs #endif .text ENTRY(strchr) and r2, r1, #0xff /* restrict to byte value */ 1: tst r0, #3 /* test for word alignment */ beq .Lpre_main_loop /* finally word aligned */ ldrb r3, [r0], #1 /* load a byte */ cmp r3, r2 /* is it a match? */ beq 2f /* yes, return current ptr - 1 */ cmp r3, #0 /* no, was it 0? */ bne 1b /* no, try next byte */ movs r0, #0 /* yes, set return value to NULL */ RET /* return */ 2: subs r0, r0, #1 /* back up by one */ RET /* return */ .Lpre_main_loop: #if defined(_ARM_ARCH_7) movw ip, #0xfefe /* magic constant; 254 in each byte */ movt ip, #0xfefe /* magic constant; 254 in each byte */ #elif defined(_ARM_ARCH_6) mov ip, #0xfe /* put 254 in low byte */ orr ip, ip, ip, lsl #8 /* move to next byte */ orr ip, ip, ip, lsl #16 /* move to next halfword */ #endif /* _ARM_ARCH_6 */ orr r2, r2, r2, lsl #8 /* move to next byte */ orr r2, r2, r2, lsl #16 /* move to next halfword */ .Lmain_loop: ldr r3, [r0], #4 /* load next word */ #if defined(_ARM_ARCH_6) /* * Add 254 to each byte using the UQADD8 (unsigned saturating add 8) * instruction. For every non-NUL byte, the result for that byte will * become 255. For NUL, it will be 254. When we complement the * result, if the result is non-0 then we must have encountered a NUL. */ uqadd8 r1, r3, ip /* NUL detection happens here */ eors r3, r3, r2 /* xor to clear each lane */ uqadd8 r3, r3, ip /* char detection happens here */ ands r3, r3, r1 /* merge results */ mvns r3, r3 /* is the complement non-0? */ beq .Lmain_loop /* no, then keep going */ /* * We've encountered a NUL or a match but we don't know which happened * first. */ #if defined(__thumb__) && defined(_ARM_ARCH_T2) cbz r2, .Lfind_match /* searching for NUL? yes, find it */ #else cmp r2, #0 /* searching for NUL? */ beq .Lfind_match /* yes, find the match */ #endif mvns r1, r1 /* did we encounter a NUL? */ beq .Lfind_match /* no, find the match */ bics r3, r3, r1 /* clear match for the NUL(s) */ beq .Lnomatch /* any left set? if not, no match */ lshis r1, r1, #8 /* replicate NUL bit to other bytes */ #ifdef __thumb__ itt ne #endif orrne r1, r1, r1, lshi #8 /* replicate NUL bit to other bytes */ orrne r1, r1, r1, lshi #8 /* replicate NUL bit to other bytes */ bics r3, r3, r1 /* clear any match bits after the NUL */ beq .Lnomatch /* any left set? if not, no match */ .Lfind_match: #ifdef __ARMEL__ rev r3, r3 /* we want this in BE for the CLZ */ #endif clz r3, r3 /* count how many leading zeros */ add r0, r0, r3, lsr #3 /* divide that by 8 and add to count */ subs r0, r0, #4 /* compensate for the post-inc */ RET .Lnomatch: movs r0, #0 RET #else /* * No fancy shortcuts so just test each byte lane for a NUL. * (other tests for NULs in a word take more instructions/cycles). */ eor r1, r3, r2 /* xor .. */ tst r3, #BYTE0 /* is this byte NUL? */ tstne r1, #BYTE0 /* no, does this byte match? */ tstne r3, #BYTE1 /* no, is this byte NUL? */ tstne r1, #BYTE1 /* no, does this byte match? */ tstne r3, #BYTE2 /* no, is this byte NUL? */ tstne r1, #BYTE2 /* no, does this byte match? */ tstne r3, #BYTE3 /* no, is this byte NUL? */ tstne r1, #BYTE3 /* no, does this byte match? */ bne .Lmain_loop sub r2, r0, #4 /* un post-inc */ mov r0, #0 /* assume no match */ tst r1, #BYTE0 /* does this byte match? */ moveq r0, r2 /* yes, point to it */ RETc(eq) /* and return */ tst r3, #BYTE0 /* is this byte NUL? */ RETc(eq) /* yes, return NULL */ tst r1, #BYTE1 /* does this byte match? */ addeq r0, r2, #1 /* yes, point to it */ RETc(eq) /* and return */ tst r3, #BYTE1 /* is this byte NUL? */ RETc(eq) /* yes, return NULL */ tst r1, #BYTE2 /* does this byte match? */ addeq r0, r2, #2 /* yes, point to it */ RETc(eq) /* and return */ tst r3, #BYTE2 /* is this byte NUL? */ RETc(eq) /* yes, return NULL */ tst r1, #BYTE3 /* does this byte match? */ addeq r0, r2, #3 /* yes, point to it */ /* * Since no NULs and no matches this must be the only case left. */ RET /* return */ #endif /* _ARM_ARCH_6 */ END(strchr)
