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99 lines
1.9 KiB
99 lines
1.9 KiB
/*
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* memset - fill memory with a constant
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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 memset routine is optimised on a Cortex-A9 and should work on
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all ARMv7 processors.
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*/
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.syntax unified
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.arch armv7-a
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@ 2011-08-30 david.gilbert@linaro.org
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@ Extracted from local git 2f11b436
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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 __memset_arm
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.type __memset_arm,%function
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__memset_arm:
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@ r0 = address
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@ r1 = character
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@ r2 = count
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@ returns original address in r0
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mov r3, r0 @ Leave r0 alone
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cbz r2, 10f @ Exit if 0 length
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tst r0, #7
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beq 2f @ Already aligned
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@ Ok, so we're misaligned here
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1:
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strb r1, [r3], #1
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subs r2,r2,#1
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tst r3, #7
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cbz r2, 10f @ Exit if we hit the end
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bne 1b @ go round again if still misaligned
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2:
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@ OK, so we're aligned
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push {r4,r5,r6,r7}
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bics r4, r2, #15 @ if less than 16 bytes then need to finish it off
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beq 5f
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3:
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@ POSIX says that ch is cast to an unsigned char. A uxtb is one
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@ byte and takes two cycles, where an AND is four bytes but one
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@ cycle.
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and r1, #0xFF
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orr r1, r1, r1, lsl#8 @ Same character into all bytes
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orr r1, r1, r1, lsl#16
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mov r5,r1
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mov r6,r1
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mov r7,r1
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4:
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subs r4,r4,#16
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stmia r3!,{r1,r5,r6,r7}
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bne 4b
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and r2,r2,#15
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@ At this point we're still aligned and we have upto align-1 bytes left to right
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@ we can avoid some of the byte-at-a time now by testing for some big chunks
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tst r2,#8
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itt ne
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subne r2,r2,#8
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stmiane r3!,{r1,r5}
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5:
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pop {r4,r5,r6,r7}
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cbz r2, 10f
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@ Got to do any last < alignment bytes
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6:
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subs r2,r2,#1
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strb r1,[r3],#1
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bne 6b
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10:
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bx lr @ goodbye
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.size __memset_arm, . - __memset_arm
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