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128 lines
4.2 KiB
ArmAsm
128 lines
4.2 KiB
ArmAsm
/* Copyright (c) 2010-2011, Linaro Limited
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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* Neither the name of Linaro Limited nor the names of its
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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Written by Dave Gilbert <david.gilbert@linaro.org>
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This strlen routine is optimised on a Cortex-A9 and should work on
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all ARMv7 processors. This routine is reasonably fast for short
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strings, but is probably slower than a simple implementation if all
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your strings are very short */
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@ 2011-02-08 david.gilbert@linaro.org
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@ Extracted from local git 6848613a
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@ 2011-10-13 david.gilbert@linaro.org
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@ Extracted from cortex-strings bzr rev 63
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@ Integrate to newlib, flip to ldrd
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@ Pull in Endian macro from my memchr
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#include "arm_asm.h"
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@ NOTE: This ifdef MUST match the ones in arm/strlen.c
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@ We fallback to the one in arm/strlen.c for size optimised or
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@ for older arch's
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#if defined(_ISA_ARM_7) || defined(__ARM_ARCH_6T2__) && \
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!(defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED) || \
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(defined (__thumb__) && !defined (__thumb2__)))
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@ this lets us check a flag in a 00/ff byte easily in either endianness
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#ifdef __ARMEB__
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#define CHARTSTMASK(c) 1<<(31-(c*8))
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#else
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#define CHARTSTMASK(c) 1<<(c*8)
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#endif
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@------------------------------------------------------------------------------
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.syntax unified
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.arch armv7-a
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.thumb_func
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.align 2
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.p2align 4,,15
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.global strlen
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.type strlen,%function
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strlen:
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@ r0 = string
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@ returns count of bytes in string not including terminator
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mov r1, r0
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push { r4,r6 }
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mvns r6, #0 @ all F
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movs r4, #0
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tst r0, #7
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beq 2f
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1:
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ldrb r2, [r1], #1
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tst r1, #7 @ Hit alignment yet?
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cbz r2, 10f @ Exit if we found the 0
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bne 1b
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@ So we're now aligned
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2:
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ldrd r2,r3,[r1],#8
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uadd8 r2, r2, r6 @ Par add 0xff - sets the GE bits for bytes!=0
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sel r2, r4, r6 @ bytes are 00 for none-00 bytes,
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@ or ff for 00 bytes - NOTE INVERSION
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uadd8 r3, r3, r6 @ Par add 0xff - sets the GE bits for bytes!=0
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sel r3, r2, r6 @ chained...bytes are 00 for none-00 bytes,
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@ or ff for 00 bytes - NOTE INVERSION
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cmp r3, #0
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beq 2b
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strlenendtmp:
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@ One (or more) of the bytes we loaded was 0 - but which one?
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@ r2 has the mask corresponding to the first loaded word
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@ r3 has a combined mask of the two words - but if r2 was all-non 0
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@ then it's just the 2nd words
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cmp r2, #0
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itte eq
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moveq r2, r3 @ the end is in the 2nd word
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subeq r1,r1,#3
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subne r1,r1,#7
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@ r1 currently points to the 2nd byte of the word containing the 0
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tst r2, # CHARTSTMASK(0) @ 1st character
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bne 10f
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adds r1,r1,#1
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tst r2, # CHARTSTMASK(1) @ 2nd character
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ittt eq
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addeq r1,r1,#1
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tsteq r2, # (3<<15) @ 2nd & 3rd character
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@ If not the 3rd must be the last one
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addeq r1,r1,#1
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10:
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@ r0 is still at the beginning, r1 is pointing 1 byte after the nul
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sub r0, r1, r0
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subs r0, r0, #1
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pop { r4, r6 }
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bx lr
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#endif
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