sysdeps/libm-ieee754/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) = 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 __ilogb(double x)
  28 #else
  29         int __ilogb(x)
  30         double x;
  31 #endif
  32 {
  33         int32_t hx,lx,ix;
  34
  35         GET_HIGH_WORD(hx,x);
  36         hx &= 0x7fffffff;
  37         if(hx<0x00100000) {
  38             GET_LOW_WORD(lx,x);
  39             if((hx|lx)==0)
  40                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  41             else                        /* subnormal x */
  42                 if(hx==0) {
  43                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  44                 } else {
  45                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  46                 }
  47             return ix;
  48         }
  49         else if (hx<0x7ff00000) return (hx>>20)-1023;
  50         else return 0x7fffffff;
  51 }
  52 weak_alias (__ilogb, ilogb)
  53 #ifdef NO_LONG_DOUBLE
  54 strong_alias (__ilogb, __ilogbl)
  55 weak_alias (__ilogb, ilogbl)
  56 #endif