sysdeps/ieee754/dbl-64/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, rix;
  26
  27   EXTRACT_WORDS (ix, lx, x);
  28   ix &= 0x7fffffff;             /* high |x| */
  29   if ((ix | lx) == 0)
  30     return -1.0 / fabs (x);
  31   if (ix >= 0x7ff00000)
  32     return x * x;
  33   if (__glibc_unlikely ((rix = ix >> 20) == 0))
  34     {
  35       /* POSIX specifies that denormal number is treated as
  36          though it were normalized.  */
  37       int ma;
  38       if (ix == 0)
  39         ma = __builtin_clz (lx) + 32;
  40       else
  41         ma = __builtin_clz (ix);
  42       rix -= ma - 12;
  43     }
  44   return (double) (rix - 1023);
  45 }
  46 weak_alias (__logb, logb)
  47 #ifdef NO_LONG_DOUBLE
  48 strong_alias (__logb, __logbl) weak_alias (__logb, logbl)
  49 #endif