libm/s_logb.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * double logb(x)
  14  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  15  * Use ilogb instead.
  16  */
  17
  18 #include "math.h"
  19 #include "math_private.h"
  20
  21 double logb(double x)
  22 {
  23         int32_t lx,ix;
  24         EXTRACT_WORDS(ix,lx,x);
  25         ix &= 0x7fffffff;                       /* high |x| */
  26         if((ix|lx)==0) return -1.0/fabs(x);
  27         if(ix>=0x7ff00000) return x*x;
  28         if((ix>>=20)==0)                        /* IEEE 754 logb */
  29                 return -1022.0;
  30         else
  31                 return (double) (ix-1023);
  32 }
  33 libm_hidden_def(logb)