js/src/fdlibm/s_ilogb.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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  15  *
  16  * The Original Code is Mozilla Communicator client code, released
  17  * March 31, 1998.
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  19  * The Initial Developer of the Original Code is
  20  * Sun Microsystems, Inc.
  21  * Portions created by the Initial Developer are Copyright (C) 1998
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  39
  40 /* @(#)s_ilogb.c 1.3 95/01/18 */
  41 /*
  42  * ====================================================
  43  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  44  *
  45  * Developed at SunSoft, a Sun Microsystems, Inc. business.
  46  * Permission to use, copy, modify, and distribute this
  47  * software is freely granted, provided that this notice
  48  * is preserved.
  49  * ====================================================
  50  */
  51
  52 /* ilogb(double x)
  53  * return the binary exponent of non-zero x
  54  * ilogb(0) = 0x80000001
  55  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  56  */
  57
  58 #include "fdlibm.h"
  59
  60 #ifdef __STDC__
  61         int fd_ilogb(double x)
  62 #else
  63         int fd_ilogb(x)
  64         double x;
  65 #endif
  66 {
  67         int hx,lx,ix;
  68         fd_twoints u;
  69         u.d = x;
  70         hx  = (__HI(u))&0x7fffffff;     /* high word of x */
  71         if(hx<0x00100000) {
  72             lx = __LO(u);
  73             if((hx|lx)==0)
  74                 return 0x80000001;      /* ilogb(0) = 0x80000001 */
  75             else                        /* subnormal x */
  76                 if(hx==0) {
  77                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  78                 } else {
  79                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  80                 }
  81             return ix;
  82         }
  83         else if (hx<0x7ff00000) return (hx>>20)-1023;
  84         else return 0x7fffffff;
  85 }