lib/libm/src/w_log2.c

   1 /* @(#)w_log10.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 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: w_log2.c,v 1.1 2005/07/21 16:58:39 christos Exp $");
  16 #endif
  17
  18 /*
  19  * wrapper log2(X)
  20  */
  21
  22 #include "math.h"
  23 #include "math_private.h"
  24
  25
  26 double
  27 log2(double x)          /* wrapper log10 */
  28 {
  29 #ifdef _IEEE_LIBM
  30         return __ieee754_log2(x);
  31 #else
  32         double z;
  33         z = __ieee754_log2(x);
  34         if(_LIB_VERSION == _IEEE_ || isnan(x)) return z;
  35         if(x<=0.0) {
  36             if(x==0.0)
  37                 return __kernel_standard(x,x,48); /* log2(0) */
  38             else
  39                 return __kernel_standard(x,x,49); /* log2(x<0) */
  40         } else
  41             return z;
  42 #endif
  43 }