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