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  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 */
  65.