compiler/stdc/math/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 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ilogb.c,v 1.9 2004/10/09 17:14:28 stefanf 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
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29         int ilogb(double x)
  30 {
  31         int32_t hx,lx,ix;
  32
  33         EXTRACT_WORDS(hx,lx,x);
  34         hx &= 0x7fffffff;
  35         if(hx<0x00100000) {
  36             if((hx|lx)==0)
  37                 return FP_ILOGB0;
  38             else                        /* subnormal x */
  39                 if(hx==0) {
  40                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  41                 } else {
  42                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  43                 }
  44             return ix;
  45         }
  46         else if (hx<0x7ff00000) return (hx>>20)-1023;
  47         else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
  48         else return INT_MAX;
  49 }