sysdeps/libm-ieee754/s_logb.c

   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 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_logb.c,v 1.8 1995/05/10 20:47:50 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 weak_alias (__logb, logb)
  44 #ifdef NO_LONG_DOUBLE
  45 strong_alias (__logb, __logbl)
  46 weak_alias (__logb, logbl)
  47 #endif