compiler/mlib/s_scalbn.c

   1 /* @(#)s_scalbn.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 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_scalbn.c,v 1.6 1999/08/28 00:06:54 peter Exp $";
  15 #endif
  16
  17 /*
  18  * scalbn (double x, int n)
  19  * scalbn(x,n) returns x* 2**n  computed by  exponent
  20  * manipulation rather than by actually performing an
  21  * exponentiation or a multiplication.
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 #ifdef __STDC__
  28 static const double
  29 #else
  30 static double
  31 #endif
  32 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  33 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  34 huge   = 1.0e+300,
  35 tiny   = 1.0e-300;
  36
  37 #ifdef __STDC__
  38         double __generic_scalbn (double x, int n)
  39 #else
  40         double __generic_scalbn (x,n)
  41         double x; int n;
  42 #endif
  43 {
  44         int32_t k,hx,lx;
  45         EXTRACT_WORDS(hx,lx,x);
  46         k = (hx&0x7ff00000)>>20;                /* extract exponent */
  47         if (k==0) {                             /* 0 or subnormal x */
  48             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  49             x *= two54;
  50             GET_HIGH_WORD(hx,x);
  51             k = ((hx&0x7ff00000)>>20) - 54;
  52             if (n< -50000) return tiny*x;       /*underflow*/
  53             }
  54         if (k==0x7ff) return x+x;               /* NaN or Inf */
  55         k = k+n;
  56         if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
  57         if (k > 0)                              /* normal result */
  58             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  59         if (k <= -54)
  60             if (n > 50000)      /* in case integer overflow in n+k */
  61                 return huge*copysign(huge,x);   /*overflow*/
  62             else return tiny*copysign(tiny,x);  /*underflow*/
  63         k += 54;                                /* subnormal result */
  64         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
  65         return x*twom54;
  66 }