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
  13 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_logb.c,v 1.12 2011/08/03 14:13:07 joerg Exp $");
  16 #endif
  17
  18 /*
  19  * double logb(x)
  20  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  21  * Use ilogb instead.
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 #ifndef __HAVE_LONG_DOUBLE
  28 __strong_alias(logbl,logb)
  29 #endif
  30
  31 double
  32 logb(double x)
  33 {
  34         int32_t lx,ix;
  35         EXTRACT_WORDS(ix,lx,x);
  36         ix &= 0x7fffffff;                       /* high |x| */
  37         if((ix|lx)==0) return -1.0/fabs(x);
  38         if(ix>=0x7ff00000) return x*x;
  39         if((ix>>=20)==0)                        /* IEEE 754 logb */
  40                 return -1022.0;
  41         else
  42                 return (double) (ix-1023);
  43 }