compiler/mlib/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 1.6 1999/08/28 00:06:49 peter Exp $";
  15 #endif
  16
  17 /* ilogb(double x)
  18  * return the binary exponent of non-zero x
  19  * ilogb(0) = 0x80000001
  20  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  21  */
  22
  23 #include "math.h"
  24 #include "math_private.h"
  25
  26 #ifdef __STDC__
  27         int __generic_ilogb(double x)
  28 #else
  29         int __generic_ilogb(x)
  30         double x;
  31 #endif
  32 {
  33         int32_t hx,lx,ix;
  34
  35         EXTRACT_WORDS(hx,lx,x);
  36         hx &= 0x7fffffff;
  37         if(hx<0x00100000) {
  38             if((hx|lx)==0)
  39                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  40             else                        /* subnormal x */
  41                 if(hx==0) {
  42                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  43                 } else {
  44                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  45                 }
  46             return ix;
  47         }
  48         else if (hx<0x7ff00000) return (hx>>20)-1023;
  49         else return 0x7fffffff;
  50 }