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annotate src/libsys/bzero.S @ 179:2a9935250c95

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src/cs: sync with Magnetite
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 04 Jan 2020 21:38:55 +0000
parents 425ab6d987f3
children
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86
425ab6d987f3 src/libsys: pieced together from Citrine
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1 /*
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2 * This ARM implementation of bzero() has been derived from:
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3 *
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4 * linux/arch/arm/lib/memzero.S
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5 *
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6 * Copyright (C) 1995-2000 Russell King
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7 *
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8 * This program is free software; you can redistribute it and/or modify
425ab6d987f3 src/libsys: pieced together from Citrine
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9 * it under the terms of the GNU General Public License version 2 as
425ab6d987f3 src/libsys: pieced together from Citrine
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10 * published by the Free Software Foundation.
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11 */
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12
425ab6d987f3 src/libsys: pieced together from Citrine
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13 .text
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14 .code 32
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15 .globl bzero
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16
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17 /*
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18 * Align the pointer in r0. r3 contains the number of bytes that we are
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19 * mis-aligned by, and r1 is the number of bytes. If r1 < 4, then we
425ab6d987f3 src/libsys: pieced together from Citrine
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20 * don't bother; we use byte stores instead.
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21 */
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22 1: subs r1, r1, #4 @ 1 do we have enough
425ab6d987f3 src/libsys: pieced together from Citrine
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23 blt 5f @ 1 bytes to align with?
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24 cmp r3, #2 @ 1
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25 strltb r2, [r0], #1 @ 1
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26 strleb r2, [r0], #1 @ 1
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27 strb r2, [r0], #1 @ 1
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28 add r1, r1, r3 @ 1 (r1 = r1 - (4 - r3))
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29 /*
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30 * The pointer is now aligned and the length is adjusted. Try doing the
425ab6d987f3 src/libsys: pieced together from Citrine
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31 * bzero again.
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32 */
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33
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34 bzero:
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35 mov r2, #0 @ 1
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36 ands r3, r0, #3 @ 1 unaligned?
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37 bne 1b @ 1
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38 /*
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39 * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary.
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40 */
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41 3: subs r1, r1, #4
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42 strge r2, [r0], #4
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43 bgt 3b @ 1
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44 bxeq lr @ 1/2 quick exit
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45 /*
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46 * No need to correct the count; we're only testing bits from now on
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47 *
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48 * When we get here, we've got less than 4 bytes to zero. We
425ab6d987f3 src/libsys: pieced together from Citrine
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49 * may have an unaligned pointer as well.
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50 */
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51 5: tst r1, #2 @ 1 2 bytes or more?
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52 strneb r2, [r0], #1 @ 1
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53 strneb r2, [r0], #1 @ 1
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54 tst r1, #1 @ 1 a byte left over
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55 strneb r2, [r0], #1 @ 1
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56 bx lr @ 1