161 lines
4.9 KiB
ArmAsm
161 lines
4.9 KiB
ArmAsm
/* Copyright (C) 2011-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
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@ and ARMv6T2 processors. It has a fast path for short sizes, and has an
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@ optimised path for large data sets; the worst case is finding the match early
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@ in a large data set.
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@ Note: The use of cbz/cbnz means it's Thumb only
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@ 2011-07-15 david.gilbert@linaro.org
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@ Copy from Cortex strings release 21 and change license
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@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
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@ Change function declarations/entry/exit
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@ 2011-12-01 david.gilbert@linaro.org
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@ Add some fixes from comments received (including use of ldrd instead ldm)
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@ 2011-12-07 david.gilbert@linaro.org
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@ Removed cbz from align loop - can't be taken
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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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.syntax unified
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.text
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.thumb
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.thumb_func
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.global memchr
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.type memchr,%function
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ENTRY(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 think we can trust the caller to actually pass a char
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cmp r2,#16 @ If it's 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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bne 5b @ If not aligned yet then do next byte
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10:
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@ At this point, 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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cfi_adjust_cfa_offset (16)
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cfi_rel_offset (r4, 0)
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cfi_rel_offset (r5, 4)
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cfi_rel_offset (r6, 8)
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cfi_rel_offset (r7, 12)
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cfi_remember_state
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orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
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orr r1, r1, r1, lsl #16
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bic r6, 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 r4,r5, [r0],#8
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subs r6, r6, #8
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eor r4,r4, r1 @ Get it so that r4,r5 have 00's where the bytes match the target
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eor r5,r5, r1
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uadd8 r4, r4, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
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sel r4, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
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uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
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sel r5, r4, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
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cbnz r5, 60f
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bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
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pop {r4,r5,r6,r7}
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cfi_adjust_cfa_offset (-16)
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cfi_restore (r4)
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cfi_restore (r5)
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cfi_restore (r6)
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cfi_restore (r7)
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and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
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and r2,r2,#7 @ Leave the count remaining as the number 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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DO_RET(lr)
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50:
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subs r0,r0,#1 @ found
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DO_RET(lr)
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60: @ We're here because the fast path found a hit - 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 that was tested
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@ r4 has the 00/ff pattern for the first word, r5 has the chained value
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cfi_restore_state
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cmp r4, #0
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itte eq
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moveq r4, r5 @ 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 r4, # CHARTSTMASK(0) @ 1st character
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bne 61f
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adds r0,r0,#1
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tst r4, # CHARTSTMASK(1) @ 2nd character
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ittt eq
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addeq r0,r0,#1
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tsteq r4, # (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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cfi_adjust_cfa_offset (-16)
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cfi_restore (r4)
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cfi_restore (r5)
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cfi_restore (r6)
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cfi_restore (r7)
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subs r0,r0,#1
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DO_RET(lr)
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END(memchr)
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libc_hidden_builtin_def (memchr)
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