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/*-
* 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 1.9 2014/05/06 16:02:11 joerg 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? */
bge .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 0? */
tstne r3, #BYTE2 /* no, is this byte 0? */
tstne r3, #BYTE3 /* no, is this byte 0? */
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 gt
#endif
movgt 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)
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