/*- * Copyright (c) 2012 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: strlen_arm.S,v 1.11 2023/01/15 08:43:03 skrll 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 #else #define BYTE0 0xff000000 #define BYTE1 0x00ff0000 #define BYTE2 0x0000ff00 #define BYTE3 0x000000ff #endif #ifdef STRNLEN #define FUNCNAME strnlen #else #define FUNCNAME strlen #endif .text ENTRY(FUNCNAME) #if defined(__ARM_EABI__) && defined(__UNWIND_TABLES__) # if !defined(__ARM_DWARF_EH__) .fnstart # endif .cfi_startproc #endif #ifdef STRNLEN push {r4,r5} /* save some registers */ #if defined(__ARM_EABI__) && defined(__UNWIND_TABLES__) # if !defined(__ARM_DWARF_EH__) .save {r4,r5} # endif .cfi_def_cfa_offset 8 .cfi_offset 5, -4 .cfi_offset 4, -8 #endif adds r5, r0, r1 /* get ptr to end of string */ mov r4, r1 /* save maxlen */ #endif adds r2, r0, #4 /* for the final post-inc */ 1: tst r0, #3 /* test for word alignment */ beq .Lpre_main_loop /* finally word aligned */ #ifdef STRNLEN cmp r0, r5 /* have we gone too far? */ beq .Lmaxed_out /* yes, return maxlen */ #endif ldrb r3, [r0], #1 /* load a byte */ cmp r3, #0 /* is it 0? */ bne 1b /* no, try next byte */ subs r2, r2, #3 /* subtract (4 - the NUL) */ subs r0, r0, r2 /* subtract start */ #ifdef STRNLEN pop {r4, r5} /* restore registers */ #endif RET /* return */ .Lpre_main_loop: #if defined(_ARM_ARCH_7) movw r1, #0xfefe /* magic constant; 254 in each byte */ movt r1, #0xfefe /* magic constant; 254 in each byte */ #elif defined(_ARM_ARCH_6) mov r1, #0xfe /* put 254 in low byte */ orr r1, r1, r1, lsl #8 /* move to next byte */ orr r1, r1, r1, lsl #16 /* move to next halfword */ #endif /* _ARM_ARCH_6 */ .Lmain_loop: #ifdef STRNLEN cmp r0, r5 /* gone too far? */ bhs .Lmaxed_out /* yes, return maxlen */ #endif 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 r3, r3, r1 /* magic happens here */ mvns r3, r3 /* is the complemented result non-0? */ beq .Lmain_loop /* no, then we encountered no NULs */ #else /* * No fancy shortcuts so just test each byte lane for a NUL. * (other tests for NULs in a word take more instructions/cycles). */ tst r3, #BYTE0 /* is this byte 0? */ tstne r3, #BYTE1 /* no, is this byte 1? */ tstne r3, #BYTE2 /* no, is this byte 2? */ tstne r3, #BYTE3 /* no, is this byte 3? */ bne .Lmain_loop /* no, then get next word */ #endif #if defined(_ARM_ARCH_6) /* * We encountered a NUL. Find out where by doing a CLZ and then * shifting right by 3. That will be the number of non-NUL bytes. */ #ifdef __ARMEL__ rev r3, r3 /* we want this in BE for the CLZ */ #endif clz r3, r3 /* count how many leading zeros */ #ifdef __thumb__ lsrs r3, r3, #3 adds r0, r0, r3 /* divide that by 8 and add to count */ #else add r0, r0, r3, lsr #3 /* divide that by 8 and add to count */ #endif #else /* * We encountered a NUL. */ tst r3, #BYTE0 /* 1st byte was NUL? */ beq 1f /* yes, done adding */ add r0, r0, #1 /* we have one more non-NUL byte */ tst r3, #BYTE1 /* 2nd byte was NUL? */ beq 1f /* yes, done adding */ add r0, r0, #1 /* we have one more non-NUL byte */ tst r3, #BYTE2 /* 3rd byte was NUL? */ addne r0, r0, #1 /* no, we have one more non-NUL byte */ 1: #endif /* _ARM_ARCH_6 */ /* * r0 now points to 4 past the NUL due to the post-inc. Subtract the * start of the string (which also has 4 added to it to compensate for * the post-inc. */ subs r0, r0, r2 /* subtract start to get length */ #ifdef STRNLEN cmp r0, r4 /* is it larger than maxlen? */ #ifdef __thumb__ it hi #endif movhi r0, r4 /* yes, return maxlen */ pop {r4, r5} /* restore registers */ #endif RET /* return */ #ifdef STRNLEN .Lmaxed_out: mov r0, r4 /* return maxlen */ pop {r4, r5} /* restore registers */ RET /* return */ #endif #if defined(__ARM_EABI__) && defined(__UNWIND_TABLES__) .cfi_endproc # if !defined(__ARM_DWARF_EH__) .fnend # endif #endif END(FUNCNAME)
