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 #include <sys/cdefs.h> 14 __FBSDID("$FreeBSD$"); 15 16 /* 17 * double logb(x) 18 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 19 * Use ilogb instead. 20 */ 21 22 #include <float.h> 23 24 #include "math.h" 25 #include "math_private.h" 26 27 static const double 28 two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 29 30 double 31 logb(double x) 32 { 33 int32_t lx,ix; 34 EXTRACT_WORDS(ix,lx,x); 35 ix &= 0x7fffffff; /* high |x| */ 36 if((ix|lx)==0) return -1.0/fabs(x); 37 if(ix>=0x7ff00000) return x*x; 38 if(ix<0x00100000) { 39 x *= two54; /* convert subnormal x to normal */ 40 GET_HIGH_WORD(ix,x); 41 ix &= 0x7fffffff; 42 return (double) ((ix>>20)-1023-54); 43 } else 44 return (double) ((ix>>20)-1023); 45 } 46 47 #if (LDBL_MANT_DIG == 53) 48 __weak_reference(logb, logbl); 49 #endif 50