FreeCalypso > hg > fc-selenite
comparison src/libsys/bzero.S @ 86:425ab6d987f3
src/libsys: pieced together from Citrine
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Fri, 20 Jul 2018 20:36:19 +0000 |
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| children |
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| 85:4ef6808ea50e | 86:425ab6d987f3 |
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| 1 /* | |
| 2 * This ARM implementation of bzero() has been derived from: | |
| 3 * | |
| 4 * linux/arch/arm/lib/memzero.S | |
| 5 * | |
| 6 * Copyright (C) 1995-2000 Russell King | |
| 7 * | |
| 8 * This program is free software; you can redistribute it and/or modify | |
| 9 * it under the terms of the GNU General Public License version 2 as | |
| 10 * published by the Free Software Foundation. | |
| 11 */ | |
| 12 | |
| 13 .text | |
| 14 .code 32 | |
| 15 .globl bzero | |
| 16 | |
| 17 /* | |
| 18 * Align the pointer in r0. r3 contains the number of bytes that we are | |
| 19 * mis-aligned by, and r1 is the number of bytes. If r1 < 4, then we | |
| 20 * don't bother; we use byte stores instead. | |
| 21 */ | |
| 22 1: subs r1, r1, #4 @ 1 do we have enough | |
| 23 blt 5f @ 1 bytes to align with? | |
| 24 cmp r3, #2 @ 1 | |
| 25 strltb r2, [r0], #1 @ 1 | |
| 26 strleb r2, [r0], #1 @ 1 | |
| 27 strb r2, [r0], #1 @ 1 | |
| 28 add r1, r1, r3 @ 1 (r1 = r1 - (4 - r3)) | |
| 29 /* | |
| 30 * The pointer is now aligned and the length is adjusted. Try doing the | |
| 31 * bzero again. | |
| 32 */ | |
| 33 | |
| 34 bzero: | |
| 35 mov r2, #0 @ 1 | |
| 36 ands r3, r0, #3 @ 1 unaligned? | |
| 37 bne 1b @ 1 | |
| 38 /* | |
| 39 * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary. | |
| 40 */ | |
| 41 3: subs r1, r1, #4 | |
| 42 strge r2, [r0], #4 | |
| 43 bgt 3b @ 1 | |
| 44 bxeq lr @ 1/2 quick exit | |
| 45 /* | |
| 46 * No need to correct the count; we're only testing bits from now on | |
| 47 * | |
| 48 * When we get here, we've got less than 4 bytes to zero. We | |
| 49 * may have an unaligned pointer as well. | |
| 50 */ | |
| 51 5: tst r1, #2 @ 1 2 bytes or more? | |
| 52 strneb r2, [r0], #1 @ 1 | |
| 53 strneb r2, [r0], #1 @ 1 | |
| 54 tst r1, #1 @ 1 a byte left over | |
| 55 strneb r2, [r0], #1 @ 1 | |
| 56 bx lr @ 1 |