lib/libm/src/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  * $NetBSD: s_logb.c,v 1.11 2002/05/26 22:01:57 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/s_logb.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /*
  17  * double logb(x)
  18  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  19  * Use ilogb instead.
  20  */
  21
  22 #include <math.h>
  23 #include "math_private.h"
  24
  25 double
  26 logb(double x)
  27 {
  28         int32_t lx,ix;
  29         EXTRACT_WORDS(ix,lx,x);
  30         ix &= 0x7fffffff;                       /* high |x| */
  31         if((ix|lx)==0) return -1.0/fabs(x);
  32         if(ix>=0x7ff00000) return x*x;
  33         if((ix>>=20)==0)                        /* IEEE 754 logb */
  34                 return -1022.0;
  35         else
  36                 return (double) (ix-1023);
  37 }