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133 lines
3.7 KiB
133 lines
3.7 KiB
/*
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* memchr - scan memory for a character
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*
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* Copyright (c) 2010-2021, Arm Limited.
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* SPDX-License-Identifier: MIT
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*/
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/*
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Written by Dave Gilbert <david.gilbert@linaro.org>
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This __memchr_arm routine is optimised on a Cortex-A9 and should work on
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all ARMv7 processors. It has a fast past 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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*/
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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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@ 2011-12-07 david.gilbert@linaro.org
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@ Removed unneeded cbz from align loop
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.syntax unified
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.arch armv7-a
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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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.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_arm
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.type __memchr_arm,%function
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__memchr_arm:
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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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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 r4, r2, #7 @ Number of double words to work with
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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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ldmia r0!,{r5,r6}
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subs r4, r4, #8
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eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target
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eor r6,r6, r1
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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, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
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uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
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sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, 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) If not run out of bytes then go around again
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pop {r4,r5,r6,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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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 - 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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@ 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 3rd 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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.size __memchr_arm, . - __memchr_arm
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