| The Android Open Source Project | 1dc9e47 | 2009-03-03 19:28:35 -0800 | [diff] [blame] | 1 | /* @(#)s_logb.c 5.1 93/09/24 */ |
| 2 | /* |
| 3 | * ==================================================== |
| 4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 5 | * |
| 6 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
| 7 | * Permission to use, copy, modify, and distribute this |
| 8 | * software is freely granted, provided that this notice |
| 9 | * is preserved. |
| 10 | * ==================================================== |
| 11 | */ |
| 12 | |
| 13 | #ifndef lint |
| 14 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_logb.c,v 1.10 2005/12/03 11:57:19 bde Exp $"; |
| 15 | #endif |
| 16 | |
| 17 | /* |
| 18 | * double logb(x) |
| 19 | * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. |
| 20 | * Use ilogb instead. |
| 21 | */ |
| 22 | |
| 23 | #include "math.h" |
| 24 | #include "math_private.h" |
| 25 | |
| 26 | static const double |
| 27 | two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ |
| 28 | |
| 29 | double |
| 30 | logb(double x) |
| 31 | { |
| 32 | int32_t lx,ix; |
| 33 | EXTRACT_WORDS(ix,lx,x); |
| 34 | ix &= 0x7fffffff; /* high |x| */ |
| 35 | if((ix|lx)==0) return -1.0/fabs(x); |
| 36 | if(ix>=0x7ff00000) return x*x; |
| 37 | if(ix<0x00100000) { |
| 38 | x *= two54; /* convert subnormal x to normal */ |
| 39 | GET_FLOAT_WORD(ix,x); |
| 40 | ix &= 0x7fffffff; |
| 41 | return (float) ((ix>>20)-1023-54); |
| 42 | } else |
| 43 | return (double) ((ix>>20)-1023); |
| 44 | } |