libm/s_ilogb.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /* ilogb(double x)
  13  * return the binary exponent of non-zero x
  14  * ilogb(0) = 0x80000001
  15  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  16  */
  17
  18 #include "math.h"
  19 #include "math_private.h"
  20
  21 int ilogb(double x)
  22 {
  23         int32_t hx,lx,ix;
  24
  25         GET_HIGH_WORD(hx,x);
  26         hx &= 0x7fffffff;
  27         if(hx<0x00100000) {
  28             GET_LOW_WORD(lx,x);
  29             if((hx|lx)==0)
  30                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  31             else                        /* subnormal x */
  32                 if(hx==0) {
  33                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  34                 } else {
  35                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  36                 }
  37             return ix;
  38         }
  39         else if (hx<0x7ff00000) return (hx>>20)-1023;
  40         else return 0x7fffffff;
  41 }
  42 libm_hidden_def(ilogb)