sysdeps/ieee754/dbl-64/e_ilogb.c

   1 /* @(#)s_ilogb.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 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
  15 #endif
  16
  17 /* ilogb(double x)
  18  * return the binary exponent of non-zero x
  19  * ilogb(0) = FP_ILOGB0
  20  * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
  21  * ilogb(+-Inf) = INT_MAX (no signal is raised)
  22  */
  23
  24 #include <limits.h>
  25 #include <math.h>
  26 #include <math_private.h>
  27
  28 int
  29 __ieee754_ilogb (double x)
  30 {
  31   int32_t hx, lx, ix;
  32
  33   GET_HIGH_WORD (hx, x);
  34   hx &= 0x7fffffff;
  35   if (hx < 0x00100000)
  36     {
  37       GET_LOW_WORD (lx, x);
  38       if ((hx | lx) == 0)
  39         return FP_ILOGB0;               /* ilogb(0) = FP_ILOGB0 */
  40       else                              /* subnormal x */
  41       if (hx == 0)
  42         {
  43           for (ix = -1043; lx > 0; lx <<= 1)
  44             ix -= 1;
  45         }
  46       else
  47         {
  48           for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1)
  49             ix -= 1;
  50         }
  51       return ix;
  52     }
  53   else if (hx < 0x7ff00000)
  54     return (hx >> 20) - 1023;
  55   else if (FP_ILOGBNAN != INT_MAX)
  56     {
  57       /* ISO C99 requires ilogb(+-Inf) == INT_MAX.  */
  58       GET_LOW_WORD (lx, x);
  59       if (((hx ^ 0x7ff00000) | lx) == 0)
  60         return INT_MAX;
  61     }
  62   return FP_ILOGBNAN;
  63 }