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 #ifndef lint 14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_logb.c,v 1.10 2005/12/03 11:57:19 bde Exp $"; 15 #endif 16 17 /* 18 * double logb(x) 19 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 20 * Use ilogb instead. 21 */ 22 23 #include "math.h" 24 #include "math_private.h" 25 26 static const double 27 two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 28 29 double 30 logb(double x) 31 { 32 int32_t lx,ix; 33 EXTRACT_WORDS(ix,lx,x); 34 ix &= 0x7fffffff; /* high |x| */ 35 if((ix|lx)==0) return -1.0/fabs(x); 36 if(ix>=0x7ff00000) return x*x; 37 if(ix<0x00100000) { 38 x *= two54; /* convert subnormal x to normal */ 39 GET_FLOAT_WORD(ix,x); 40 ix &= 0x7fffffff; 41 return (float) ((ix>>20)-1023-54); 42 } else 43 return (double) ((ix>>20)-1023); 44 } 45
