newlib/libm/common/s_scalbln.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 /*
  14  * scalbn (double x, int n)
  15  * scalbn(x,n) returns x* 2**n  computed by  exponent
  16  * manipulation rather than by actually performing an
  17  * exponentiation or a multiplication.
  18  */
  19
  20 #include "fdlibm.h"
  21
  22 #ifndef _DOUBLE_IS_32BITS
  23
  24 #ifdef __STDC__
  25 static const double
  26 #else
  27 static double
  28 #endif
  29 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  30 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  31 huge   = 1.0e+300,
  32 tiny   = 1.0e-300;
  33
  34 #ifdef __STDC__
  35         double scalbln (double x, long int n)
  36 #else
  37         double scalbln (x,n)
  38         double x; long int n;
  39 #endif
  40 {
  41         __int32_t k,hx,lx;
  42         EXTRACT_WORDS(hx,lx,x);
  43         k = (hx&0x7ff00000)>>20;                /* extract exponent */
  44         if (k==0) {                             /* 0 or subnormal x */
  45             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  46             x *= two54;
  47             GET_HIGH_WORD(hx,x);
  48             k = ((hx&0x7ff00000)>>20) - 54;
  49             }
  50         if (k==0x7ff) return x+x;               /* NaN or Inf */
  51         k = k+n;
  52         if (n> 50000 || k >  0x7fe)
  53           return huge*copysign(huge,x); /* overflow  */
  54         if (n< -50000) return tiny*copysign(tiny,x); /*underflow*/
  55         if (k > 0)                              /* normal result */
  56             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  57         if (k <= -54)
  58           return tiny*copysign(tiny,x);         /*underflow*/
  59         k += 54;                                /* subnormal result */
  60         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
  61         return x*twom54;
  62 }
  63
  64 #endif /* _DOUBLE_IS_32BITS */