projects / apple / libc.git / blame
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|---|---|---|
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1 | /* |
| 2 | * Copyright (c) 1999 Apple Computer, Inc. All rights reserved. | |
| 3 | * | |
| 4 | * @APPLE_LICENSE_HEADER_START@ | |
| 5 | * | |
| 734aad71 A |
6 | * This file contains Original Code and/or Modifications of Original Code |
| 7 | * as defined in and that are subject to the Apple Public Source License | |
| 8 | * Version 2.0 (the 'License'). You may not use this file except in | |
| 9 | * compliance with the License. Please obtain a copy of the License at | |
| 10 | * http://www.opensource.apple.com/apsl/ and read it before using this | |
| 11 | * file. | |
| 12 | * | |
| 13 | * The Original Code and all software distributed under the License are | |
| 14 | * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER | |
| e9ce8d39 A |
15 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, |
| 16 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, | |
| 734aad71 A |
17 | * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. |
| 18 | * Please see the License for the specific language governing rights and | |
| 19 | * limitations under the License. | |
| e9ce8d39 A |
20 | * |
| 21 | * @APPLE_LICENSE_HEADER_END@ | |
| 22 | */ | |
| 23 | /* Copyright (c) 1992,1997 NeXT Software, Inc. All rights reserved. | |
| 24 | * | |
| 25 | * File: libc/gen/ppc/abs.s | |
| 26 | * Author: Derek B Clegg, NeXT Software, Inc. | |
| 27 | * | |
| 28 | * HISTORY | |
| 29 | * 24-Jan-1997 Umesh Vaishampayan (umeshv@NeXT.com) | |
| 30 | * Ported to PPC. | |
| 31 | * 10-Nov-92 Derek B Clegg (dclegg@next.com) | |
| 32 | * Created. | |
| 33 | * 13-Jan-93 Derek B Clegg (dclegg@next.com) | |
| 34 | * Optimized. | |
| 35 | * | |
| 36 | * ANSI X3.159-1989: | |
| 37 | * int abs(int j); | |
| 38 | * | |
| 39 | * Description: | |
| 40 | * The `abs' function computes the absolute value of an integer `j'. | |
| 41 | * If the result cannot be represented, the behavior is undefined. | |
| 42 | * Returns: | |
| 43 | * The `abs' function returns the absolute value. | |
| 44 | */ | |
| 45 | #include <architecture/ppc/asm_help.h> | |
| 46 | #include <architecture/ppc/pseudo_inst.h> | |
| 47 | ||
| 48 | /* We calculate abs(x) as | |
| 49 | * s = x >> 31; | |
| 50 | * y = x + s; | |
| 51 | * return y ^ s; | |
| 52 | * | |
| 53 | * If x >= 0, then s = 0, so clearly we return x. On the other hand, if | |
| 54 | * x < 0, then we may write x as ~z + 1, where z = -x. In this case, | |
| 55 | * s = -1, so y = x - 1 = ~z, and hence we return -1 ^ (x - 1) = -1 ^ ~z | |
| 56 | * = z = -x. | |
| 57 | */ | |
| 58 | LEAF(_abs) | |
| 59 | srawi a1,a0,31 | |
| 60 | add a2,a1,a0 | |
| 61 | xor a0,a2,a1 | |
| 62 | blr | |
| 63 | END(_abs) |