/* @(#)s_scalbn.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
FUNCTION
<<scalbn>>, <<scalbnf>>---scale by integer
INDEX
	scalbn
INDEX
	scalbnf

ANSI_SYNOPSIS
	#include <math.h>
	double scalbn(double <[x]>, int <[y]>);
	float scalbnf(float <[x]>, int <[y]>);

TRAD_SYNOPSIS
	#include <math.h>
	double scalbn(<[x]>,<[y]>)
	double <[x]>;
	int <[y]>;
	float scalbnf(<[x]>,<[y]>)
	float <[x]>;
	int <[y]>;

DESCRIPTION
<<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times
2 to the power <[n]>.  The result is computed by manipulating the
exponent, rather than by actually performing an exponentiation or
multiplication.

RETURNS
<[x]> times 2 to the power <[n]>.

PORTABILITY
Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V
Interface Definition (Issue 2).

*/

/*
 * scalbn (double x, int n)
 * scalbn(x,n) returns x* 2**n  computed by  exponent
 * manipulation rather than by actually performing an
 * exponentiation or a multiplication.
 */

#include "fdlibm.h"

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__
static const double
#else
static double
#endif
  two54 = 1.80143985094819840000e+16,	/* 0x43500000, 0x00000000 */
  twom54 = 5.55111512312578270212e-17,	/* 0x3C900000, 0x00000000 */
  huge = 1.0e+300, tiny = 1.0e-300;

#ifdef __STDC__
double
scalbn (double x, int n)
#else
double
scalbn (x, n)
     double x;
     int n;
#endif
{
  int32_t k, hx, lx;
  EXTRACT_WORDS (hx, lx, x);
  k = (hx & 0x7ff00000) >> 20;	/* extract exponent */
  if (k == 0)
    {				/* 0 or subnormal x */
      if ((lx | (hx & 0x7fffffff)) == 0)
	return x;		/* +-0 */
      x *= two54;
      GET_HIGH_WORD (hx, x);
      k = ((hx & 0x7ff00000) >> 20) - 54;
      if (n < -50000)
	return tiny * x;	/*underflow */
    }
  if (k == 0x7ff)
    return x + x;		/* NaN or Inf */
  k = k + n;
  if (k > 0x7fe)
    return huge * copysign (huge, x);	/* overflow  */
  if (k > 0)			/* normal result */
    {
      SET_HIGH_WORD (x, (hx & 0x800fffff) | (k << 20));
      return x;
    }
  if (k <= -54)
    {
      if (n > 50000)		/* in case integer overflow in n+k */
	return huge * copysign (huge, x);	/*overflow */
      else
	return tiny * copysign (tiny, x);	/*underflow */
    }
  k += 54;			/* subnormal result */
  SET_HIGH_WORD (x, (hx & 0x800fffff) | (k << 20));
  return x * twom54;
}

#endif /* _DOUBLE_IS_32BITS */