lib/libm/src/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  * $NetBSD: s_ilogb.c,v 1.12 2002/05/26 22:01:56 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/s_ilogb.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /* ilogb(double x)
  17  * return the binary exponent of non-zero x
  18  * ilogb(0) = 0x80000001
  19  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  20  */
  21
  22 #include <math.h>
  23 #include "math_private.h"
  24
  25 int
  26 ilogb(double x)
  27 {
  28         int32_t hx,lx,ix;
  29
  30         GET_HIGH_WORD(hx,x);
  31         hx &= 0x7fffffff;
  32         if(hx<0x00100000) {
  33             GET_LOW_WORD(lx,x);
  34             if((hx|lx)==0)
  35                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  36             else                        /* subnormal x */
  37                 if(hx==0) {
  38                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  39                 } else {
  40                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  41                 }
  42             return ix;
  43         }
  44         else if (hx<0x7ff00000) return (hx>>20)-1023;
  45         else return 0x7fffffff;
  46 }