js/src/fdlibm/s_logb.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
   2  *
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   4  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   5  *
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  12  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  13  * for the specific language governing rights and limitations under the
  14  * License.
  15  *
  16  * The Original Code is Mozilla Communicator client code, released
  17  * March 31, 1998.
  18  *
  19  * The Initial Developer of the Original Code is
  20  * Sun Microsystems, Inc.
  21  * Portions created by the Initial Developer are Copyright (C) 1998
  22  * the Initial Developer. All Rights Reserved.
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  39
  40 /* @(#)s_logb.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 /*
  53  * double logb(x)
  54  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  55  * Use ilogb instead.
  56  */
  57
  58 #include "fdlibm.h"
  59
  60 #ifdef __STDC__
  61         double fd_logb(double x)
  62 #else
  63         double fd_logb(x)
  64         double x;
  65 #endif
  66 {
  67         int lx,ix;
  68         fd_twoints u;
  69
  70         u.d = x;
  71         ix = (__HI(u))&0x7fffffff;      /* high |x| */
  72         lx = __LO(u);                   /* low x */
  73         if((ix|lx)==0) return -1.0/fd_fabs(x);
  74         if(ix>=0x7ff00000) return x*x;
  75         if((ix>>=20)==0)                        /* IEEE 754 logb */
  76                 return -1022.0;
  77         else
  78                 return (double) (ix-1023);
  79 }