contrib/openbsd_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
  13 /*
  14  * double logb(x)
  15  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  16  * Use ilogb instead.
  17  */
  18
  19 #include "math.h"
  20 #include "math_private.h"
  21
  22 double
  23 logb(double x)
  24 {
  25         int32_t lx,ix;
  26         EXTRACT_WORDS(ix,lx,x);
  27         ix &= 0x7fffffff;                       /* high |x| */
  28         if((ix|lx)==0) return -1.0/fabs(x);
  29         if(ix>=0x7ff00000) return x*x;
  30         if((ix>>=20)==0)                        /* IEEE 754 logb */
  31                 return -1022.0;
  32         else
  33                 return (double) (ix-1023);
  34 }