13a8617a8SJordan K. Hubbard /* @(#)s_logb.c 5.1 93/09/24 */ 23a8617a8SJordan K. Hubbard /* 33a8617a8SJordan K. Hubbard * ==================================================== 43a8617a8SJordan K. Hubbard * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 53a8617a8SJordan K. Hubbard * 63a8617a8SJordan K. Hubbard * Developed at SunPro, a Sun Microsystems, Inc. business. 73a8617a8SJordan K. Hubbard * Permission to use, copy, modify, and distribute this 83a8617a8SJordan K. Hubbard * software is freely granted, provided that this notice 93a8617a8SJordan K. Hubbard * is preserved. 103a8617a8SJordan K. Hubbard * ==================================================== 113a8617a8SJordan K. Hubbard */ 123a8617a8SJordan K. Hubbard 13aa7c7c47SBruce Evans #include <sys/cdefs.h> 14aa7c7c47SBruce Evans __FBSDID("$FreeBSD$"); 153a8617a8SJordan K. Hubbard 163a8617a8SJordan K. Hubbard /* 173a8617a8SJordan K. Hubbard * double logb(x) 183a8617a8SJordan K. Hubbard * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 193a8617a8SJordan K. Hubbard * Use ilogb instead. 203a8617a8SJordan K. Hubbard */ 213a8617a8SJordan K. Hubbard 226821aba9SDavid Schultz #include <float.h> 236821aba9SDavid Schultz 243a8617a8SJordan K. Hubbard #include "math.h" 253a8617a8SJordan K. Hubbard #include "math_private.h" 263a8617a8SJordan K. Hubbard 2700b1756bSBruce Evans static const double 2800b1756bSBruce Evans two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 2900b1756bSBruce Evans 3059b19ff1SAlfred Perlstein double 313819e840SPeter Wemm logb(double x) 323a8617a8SJordan K. Hubbard { 333a8617a8SJordan K. Hubbard int32_t lx,ix; 343a8617a8SJordan K. Hubbard EXTRACT_WORDS(ix,lx,x); 353a8617a8SJordan K. Hubbard ix &= 0x7fffffff; /* high |x| */ 363a8617a8SJordan K. Hubbard if((ix|lx)==0) return -1.0/fabs(x); 373a8617a8SJordan K. Hubbard if(ix>=0x7ff00000) return x*x; 3800b1756bSBruce Evans if(ix<0x00100000) { 3900b1756bSBruce Evans x *= two54; /* convert subnormal x to normal */ 40aa7c7c47SBruce Evans GET_HIGH_WORD(ix,x); 4100b1756bSBruce Evans ix &= 0x7fffffff; 42aa7c7c47SBruce Evans return (double) ((ix>>20)-1023-54); 4300b1756bSBruce Evans } else 4400b1756bSBruce Evans return (double) ((ix>>20)-1023); 453a8617a8SJordan K. Hubbard } 466821aba9SDavid Schultz 476821aba9SDavid Schultz #if (LDBL_MANT_DIG == 53) 486821aba9SDavid Schultz __weak_reference(logb, logbl); 496821aba9SDavid Schultz #endif 50