libjava/classpath/native/fdlibm/s_scalbn.c

   1
   2 /* @(#)s_scalbn.c 1.3 95/01/18 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunSoft, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15  * scalbn (double x, int n)
  16  * scalbn(x,n) returns x* 2**n  computed by  exponent
  17  * manipulation rather than by actually performing an
  18  * exponentiation or a multiplication.
  19  */
  20
  21 #include "fdlibm.h"
  22
  23 #ifndef _DOUBLE_IS_32BITS
  24
  25 #ifdef __STDC__
  26 static const double
  27 #else
  28 static double
  29 #endif
  30 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  31 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  32 huge   = 1.0e+300,
  33 tiny   = 1.0e-300;
  34
  35 #ifdef __STDC__
  36         double scalbn (double x, int n)
  37 #else
  38         double scalbn (x,n)
  39         double x; int n;
  40 #endif
  41 {
  42         int32_t  k,hx,lx;
  43         EXTRACT_WORDS(hx,lx,x);
  44         k = (hx&0x7ff00000)>>20;                /* extract exponent */
  45         if (k==0) {                             /* 0 or subnormal x */
  46             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  47             x *= two54;
  48             GET_HIGH_WORD(hx,x);
  49             k = ((hx&0x7ff00000)>>20) - 54;
  50             if (n< -50000) return tiny*x;       /*underflow*/
  51             }
  52         if (k==0x7ff) return x+x;               /* NaN or Inf */
  53         k = k+n;
  54         if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
  55         if (k > 0)                              /* normal result */
  56             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  57         if (k <= -54)
  58             if (n > 50000)      /* in case integer overflow in n+k */
  59                 return huge*copysign(huge,x);   /*overflow*/
  60             else return tiny*copysign(tiny,x);  /*underflow*/
  61         k += 54;                                /* subnormal result */
  62         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
  63         return x*twom54;
  64 }
  65 #endif /* _DOUBLE_IS_32BITS */