/****************************************************************************
 *
 * $Source: /usr/local/cvsroot/gccsdk/unixlib/source/math/scalbn.c,v $
 * $Date: 2001/01/29 15:10:19 $
 * $Revision: 1.2 $
 * $State: Exp $
 * $Author: admin $
 *
 ***************************************************************************/

/* @(#)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.
 * ====================================================
 */

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
#endif

/*
 * 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 <math.h>
#include <unixlib/math.h>
#include <unixlib/types.h>

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

double
scalbn (double x, int n)
{
  __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;
}
