167 lines
5.2 KiB
ArmAsm
167 lines
5.2 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 memchr routine is optimised on a Cortex-A9 and should work on
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all ARMv7 processors. It has a fast path for short sizes, and has
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an optimised path for large data sets; the worst case is finding the
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match early in a large data set. */
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@ 2011-02-07 david.gilbert@linaro.org
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@ Extracted from local git a5b438d861
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@ 2011-07-14 david.gilbert@linaro.org
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@ Import endianness fix from local git ea786f1b
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@ 2011-10-11 david.gilbert@linaro.org
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@ Import from cortex-strings bzr rev 63
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@ Flip to ldrd (as suggested by Greta Yorsh)
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@ Make conditional on CPU type
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@ tidy
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.syntax unified
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.arch armv7-a
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#include "arm_asm.h"
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@ NOTE: This ifdef MUST match the one in memchr-stub.c
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#if defined(_ISA_ARM_7) || defined(__ARM_ARCH_6T2__)
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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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.text
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.thumb
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@ ---------------------------------------------------------------------------
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.thumb_func
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.align 2
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.p2align 4,,15
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.global memchr
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.type memchr,%function
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memchr:
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@ r0 = start of memory to scan
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@ r1 = character to look for
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@ r2 = length
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@ returns r0 = pointer to character or NULL if not found
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and r1,r1,#0xff @ Don't trust the caller to pass a char
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cmp r2,#16 @ If short don't bother with anything clever
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blt 20f
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tst r0, #7 @ If it's already aligned skip the next bit
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beq 10f
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@ Work up to an aligned point
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5:
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ldrb r3, [r0],#1
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subs r2, r2, #1
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cmp r3, r1
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beq 50f @ If it matches exit found
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tst r0, #7
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cbz r2, 40f @ If we run off the end, exit not found
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bne 5b @ If not aligned yet then do next byte
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10:
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@ We are aligned, we know we have at least 8 bytes to work with
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push {r4,r5,r6,r7}
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orr r1, r1, r1, lsl #8 @ expand the match word across all bytes
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orr r1, r1, r1, lsl #16
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bic r4, r2, #7 @ Number of double words to work with * 8
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mvns r7, #0 @ all F's
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movs r3, #0
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15:
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ldrd r5,r6,[r0],#8
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subs r4, r4, #8
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eor r5,r5, r1 @ r5,r6 have 00's where bytes match the target
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eor r6,r6, r1
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uadd8 r5, r5, r7 @ Par add 0xff - sets GE bits for bytes!=0
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sel r5, r3, r7 @ bytes are 00 for none-00 bytes,
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@ or ff for 00 bytes - NOTE INVERSION
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uadd8 r6, r6, r7 @ Par add 0xff - sets GE bits for bytes!=0
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sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes
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@ or ff for 00 bytes - NOTE INVERSION
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cbnz r6, 60f
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bne 15b @ (Flags from the subs above)
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pop {r4,r5,r6,r7}
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and r1,r1,#0xff @ r1 back to a single character
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and r2,r2,#7 @ Leave the count remaining as the number
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@ after the double words have been done
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20:
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cbz r2, 40f @ 0 length or hit the end already then not found
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21: @ Post aligned section, or just a short call
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ldrb r3,[r0],#1
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subs r2,r2,#1
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eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
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cbz r3, 50f
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bne 21b @ on r2 flags
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40:
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movs r0,#0 @ not found
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bx lr
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50:
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subs r0,r0,#1 @ found
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bx lr
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60: @ We're here because the fast path found a hit
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@ now we have to track down exactly which word it was
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@ r0 points to the start of the double word after the one tested
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@ r5 has the 00/ff pattern for the first word, r6 has the chained value
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cmp r5, #0
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itte eq
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moveq r5, r6 @ the end is in the 2nd word
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subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
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subne r0,r0,#7 @ or 2nd byte of 1st word
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@ r0 currently points to the 2nd byte of the word containing the hit
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tst r5, # CHARTSTMASK(0) @ 1st character
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bne 61f
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adds r0,r0,#1
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tst r5, # CHARTSTMASK(1) @ 2nd character
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ittt eq
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addeq r0,r0,#1
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tsteq r5, # (3<<15) @ 2nd & 3rd character
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@ If not the 3rd must be the last one
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addeq r0,r0,#1
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61:
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pop {r4,r5,r6,r7}
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subs r0,r0,#1
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bx lr
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#endif
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