| /* @(#)s_logb.c 5.1 93/09/24 */ |
| /* |
| * ==================================================== |
| * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| * |
| * Developed at SunPro, a Sun Microsystems, Inc. business. |
| * Permission to use, copy, modify, and distribute this |
| * software is freely granted, provided that this notice |
| * is preserved. |
| * ==================================================== |
| */ |
| |
| #include <sys/cdefs.h> |
| __FBSDID("$FreeBSD$"); |
| |
| /* |
| * double logb(x) |
| * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. |
| * Use ilogb instead. |
| */ |
| |
| #include <float.h> |
| |
| #include "math.h" |
| #include "math_private.h" |
| |
| static const double |
| two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ |
| |
| double |
| logb(double x) |
| { |
| int32_t lx,ix; |
| EXTRACT_WORDS(ix,lx,x); |
| ix &= 0x7fffffff; /* high |x| */ |
| if((ix|lx)==0) return -1.0/fabs(x); |
| if(ix>=0x7ff00000) return x*x; |
| if(ix<0x00100000) { |
| x *= two54; /* convert subnormal x to normal */ |
| GET_HIGH_WORD(ix,x); |
| ix &= 0x7fffffff; |
| return (double) ((ix>>20)-1023-54); |
| } else |
| return (double) ((ix>>20)-1023); |
| } |
| |
| #if (LDBL_MANT_DIG == 53) |
| __weak_reference(logb, logbl); |
| #endif |
