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 133a8617a8SJordan K. Hubbard #ifndef lint 147f3dea24SPeter Wemm static char rcsid[] = "$FreeBSD$"; 153a8617a8SJordan K. Hubbard #endif 163a8617a8SJordan K. Hubbard 173a8617a8SJordan K. Hubbard /* 183a8617a8SJordan K. Hubbard * double logb(x) 193a8617a8SJordan K. Hubbard * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 203a8617a8SJordan K. Hubbard * Use ilogb instead. 213a8617a8SJordan K. Hubbard */ 223a8617a8SJordan K. Hubbard 236821aba9SDavid Schultz #include <float.h> 246821aba9SDavid Schultz 253a8617a8SJordan K. Hubbard #include "math.h" 263a8617a8SJordan K. Hubbard #include "math_private.h" 273a8617a8SJordan K. Hubbard 2800b1756bSBruce Evans static const double 2900b1756bSBruce Evans two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 3000b1756bSBruce Evans 3159b19ff1SAlfred Perlstein double 323819e840SPeter Wemm logb(double x) 333a8617a8SJordan K. Hubbard { 343a8617a8SJordan K. Hubbard int32_t lx,ix; 353a8617a8SJordan K. Hubbard EXTRACT_WORDS(ix,lx,x); 363a8617a8SJordan K. Hubbard ix &= 0x7fffffff; /* high |x| */ 373a8617a8SJordan K. Hubbard if((ix|lx)==0) return -1.0/fabs(x); 383a8617a8SJordan K. Hubbard if(ix>=0x7ff00000) return x*x; 3900b1756bSBruce Evans if(ix<0x00100000) { 4000b1756bSBruce Evans x *= two54; /* convert subnormal x to normal */ 4100b1756bSBruce Evans GET_FLOAT_WORD(ix,x); 4200b1756bSBruce Evans ix &= 0x7fffffff; 4300b1756bSBruce Evans return (float) ((ix>>20)-1023-54); 4400b1756bSBruce Evans } else 4500b1756bSBruce Evans return (double) ((ix>>20)-1023); 463a8617a8SJordan K. Hubbard } 476821aba9SDavid Schultz 486821aba9SDavid Schultz #if (LDBL_MANT_DIG == 53) 496821aba9SDavid Schultz __weak_reference(logb, logbl); 506821aba9SDavid Schultz #endif 51