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s_logb.c revision 1.6 
      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[] = "$Id: s_logb.c,v 1.6 1994/08/18 23:07:04 jtc 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 #ifdef __STDC__
     27 	double logb(double x)
     28 #else
     29 	double logb(x)
     30 	double x;
     31 #endif
     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>>=20)==0) 			/* IEEE 754 logb */
     39 		return -1022.0;
     40 	else
     41 		return (double) (ix-1023);
     42 }
     43