| | 1 | /* |
| | 2 | * Copyright (c) 1999 Apple Computer, Inc. All rights reserved. |
| | 3 | * |
| | 4 | * @APPLE_LICENSE_HEADER_START@ |
| | 5 | * |
| | 6 | * The contents of this file constitute Original Code as defined in and |
| | 7 | * are subject to the Apple Public Source License Version 1.1 (the |
| | 8 | * "License"). You may not use this file except in compliance with the |
| | 9 | * License. Please obtain a copy of the License at |
| | 10 | * http://www.apple.com/publicsource and read it before using this file. |
| | 11 | * |
| | 12 | * This Original Code and all software distributed under the License are |
| | 13 | * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER |
| | 14 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, |
| | 15 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, |
| | 16 | * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the |
| | 17 | * License for the specific language governing rights and limitations |
| | 18 | * under the License. |
| | 19 | * |
| | 20 | * @APPLE_LICENSE_HEADER_END@ |
| | 21 | */ |
| | 22 | /* Copyright (c) 1992,1997 NeXT Software, Inc. All rights reserved. |
| | 23 | * |
| | 24 | * File: libc/gen/ppc/abs.s |
| | 25 | * Author: Derek B Clegg, NeXT Software, Inc. |
| | 26 | * |
| | 27 | * HISTORY |
| | 28 | * 24-Jan-1997 Umesh Vaishampayan (umeshv@NeXT.com) |
| | 29 | * Ported to PPC. |
| | 30 | * 10-Nov-92 Derek B Clegg (dclegg@next.com) |
| | 31 | * Created. |
| | 32 | * 13-Jan-93 Derek B Clegg (dclegg@next.com) |
| | 33 | * Optimized. |
| | 34 | * |
| | 35 | * ANSI X3.159-1989: |
| | 36 | * int abs(int j); |
| | 37 | * |
| | 38 | * Description: |
| | 39 | * The `abs' function computes the absolute value of an integer `j'. |
| | 40 | * If the result cannot be represented, the behavior is undefined. |
| | 41 | * Returns: |
| | 42 | * The `abs' function returns the absolute value. |
| | 43 | */ |
| | 44 | #include <architecture/ppc/asm_help.h> |
| | 45 | #include <architecture/ppc/pseudo_inst.h> |
| | 46 | |
| | 47 | /* We calculate abs(x) as |
| | 48 | * s = x >> 31; |
| | 49 | * y = x + s; |
| | 50 | * return y ^ s; |
| | 51 | * |
| | 52 | * If x >= 0, then s = 0, so clearly we return x. On the other hand, if |
| | 53 | * x < 0, then we may write x as ~z + 1, where z = -x. In this case, |
| | 54 | * s = -1, so y = x - 1 = ~z, and hence we return -1 ^ (x - 1) = -1 ^ ~z |
| | 55 | * = z = -x. |
| | 56 | */ |
| | 57 | LEAF(_abs) |
| | 58 | srawi a1,a0,31 |
| | 59 | add a2,a1,a0 |
| | 60 | xor a0,a2,a1 |
| | 61 | blr |
| | 62 | END(_abs) |
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