sysdeps/ieee754/dbl-64/s_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 #ifdef __STDC__
  29         int __ilogb(double x)
  30 #else
  31         int __ilogb(x)
  32         double x;
  33 #endif
  34 {
  35         int32_t hx,lx,ix;
  36
  37         GET_HIGH_WORD(hx,x);
  38         hx &= 0x7fffffff;
  39         if(hx<0x00100000) {
  40             GET_LOW_WORD(lx,x);
  41             if((hx|lx)==0)
  42                 return FP_ILOGB0;       /* ilogb(0) = FP_ILOGB0 */
  43             else                        /* subnormal x */
  44                 if(hx==0) {
  45                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  46                 } else {
  47                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  48                 }
  49             return ix;
  50         }
  51         else if (hx<0x7ff00000) return (hx>>20)-1023;
  52         else if (FP_ILOGBNAN != INT_MAX) {
  53             /* ISO C99 requires ilogb(+-Inf) == INT_MAX.  */
  54             GET_LOW_WORD(lx,x);
  55             if(((hx^0x7ff00000)|lx) == 0)
  56                 return INT_MAX;
  57         }
  58         return FP_ILOGBNAN;
  59 }
  60 weak_alias (__ilogb, ilogb)
  61 #ifdef NO_LONG_DOUBLE
  62 strong_alias (__ilogb, __ilogbl)
  63 weak_alias (__ilogb, ilogbl)
  64 #endif