libjava/java/lang/s_scalbn.c

   1
   2 /* @(#)s_scalbn.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, 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 FUNCTION
  16 <<scalbn>>, <<scalbnf>>---scale by integer
  17 INDEX
  18         scalbn
  19 INDEX
  20         scalbnf
  21
  22 ANSI_SYNOPSIS
  23         #include <math.h>
  24         double scalbn(double <[x]>, int <[y]>);
  25         float scalbnf(float <[x]>, int <[y]>);
  26
  27 TRAD_SYNOPSIS
  28         #include <math.h>
  29         double scalbn(<[x]>,<[y]>)
  30         double <[x]>;
  31         int <[y]>;
  32         float scalbnf(<[x]>,<[y]>)
  33         float <[x]>;
  34         int <[y]>;
  35
  36 DESCRIPTION
  37 <<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times
  38 2 to the power <[n]>.  The result is computed by manipulating the
  39 exponent, rather than by actually performing an exponentiation or
  40 multiplication.
  41
  42 RETURNS
  43 <[x]> times 2 to the power <[n]>.
  44
  45 PORTABILITY
  46 Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V
  47 Interface Definition (Issue 2).
  48
  49 */
  50
  51 /*
  52  * scalbn (double x, int n)
  53  * scalbn(x,n) returns x* 2**n  computed by  exponent
  54  * manipulation rather than by actually performing an
  55  * exponentiation or a multiplication.
  56  */
  57
  58 #include "fdlibm.h"
  59
  60 #ifndef _DOUBLE_IS_32BITS
  61
  62 #ifdef __STDC__
  63 static const double
  64 #else
  65 static double
  66 #endif
  67 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  68 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  69 huge   = 1.0e+300,
  70 tiny   = 1.0e-300;
  71
  72 #ifdef __STDC__
  73         double scalbn (double x, int n)
  74 #else
  75         double scalbn (x,n)
  76         double x; int n;
  77 #endif
  78 {
  79         int32_t  k,hx,lx;
  80         EXTRACT_WORDS(hx,lx,x);
  81         k = (hx&0x7ff00000)>>20;                /* extract exponent */
  82         if (k==0) {                             /* 0 or subnormal x */
  83             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  84             x *= two54;
  85             GET_HIGH_WORD(hx,x);
  86             k = ((hx&0x7ff00000)>>20) - 54;
  87             if (n< -50000) return tiny*x;       /*underflow*/
  88             }
  89         if (k==0x7ff) return x+x;               /* NaN or Inf */
  90         k = k+n;
  91         if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
  92         if (k > 0)                              /* normal result */
  93             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  94         if (k <= -54) {
  95             if (n > 50000)      /* in case integer overflow in n+k */
  96                 return huge*copysign(huge,x);   /*overflow*/
  97             else return tiny*copysign(tiny,x);  /*underflow*/
  98         }
  99         k += 54;                                /* subnormal result */
 100         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
 101         return x*twom54;
 102 }
 103
 104 #endif /* _DOUBLE_IS_32BITS */