1 /* 2 * ==================================================== 3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 4 * 5 * Developed at SunPro, a Sun Microsystems, Inc. business. 6 * Permission to use, copy, modify, and distribute this 7 * software is freely granted, provided that this notice 8 * is preserved. 9 * ==================================================== 10 */ 11 12 /* 13 * double logb(x) 14 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 15 * Use ilogb instead. 16 */ 17 18 #include <float.h> 19 20 #include "math.h" 21 #include "math_private.h" 22 23 static const double 24 two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 25 26 double 27 logb(double x) 28 { 29 int32_t lx,ix; 30 EXTRACT_WORDS(ix,lx,x); 31 ix &= 0x7fffffff; /* high |x| */ 32 if((ix|lx)==0) return -1.0/fabs(x); 33 if(ix>=0x7ff00000) return x*x; 34 if(ix<0x00100000) { 35 x *= two54; /* convert subnormal x to normal */ 36 GET_HIGH_WORD(ix,x); 37 ix &= 0x7fffffff; 38 return (double) ((ix>>20)-1023-54); 39 } else 40 return (double) ((ix>>20)-1023); 41 } 42 43 #if (LDBL_MANT_DIG == 53) 44 __weak_reference(logb, logbl); 45 #endif 46