/* -*-C-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

*/

/* This file contains utilities potentially missing from the math library. */

#include "config.h"

#ifndef HAVE_FREXP

double
frexp (double value, int * eptr)
{
  double x = ((value < 0) ? (-value) : value);
  int e = 0;
  if (x >= 1)
    {
      while (1)
	{
	  if (x > 2)
	    {
	      double xr = (x / 2);
	      double r = 2;
	      int n = 1;
	      while (xr >= r)
		{
		  /* ((xr == (x / r)) && (xr >= r) && (x >= (r * r))) */
		  xr /= r;
		  /* ((xr == (x / (r * r))) && (xr >= 1)) */
		  r *= r;
		  /* ((xr == (x / r)) && (x >= r)) */
		  n += n;
		}
	      /* ((xr >= 1) && (xr < r)) */
	      x = xr;
	      e += n;
	    }
	  else if (x < 2)
	    {
	      x /= 2;
	      e += 1;
	      break;
	    }
	  else
	    {
	      x /= 4;
	      e += 2;
	      break;
	    }
	}
    }
  else if ((x > 0) && (x < 0.5))
    {
      while (1)
	{
	  if (x < 0.25)
	    {
	      double xr = (x * 2);
	      double r = 0.5;
	      int n = 1;
	      /* ((xr == (x / r)) && (xr < 0.5) && (x < (r / 2))) */
	      while (xr < (r / 2))
		{
		  /* ((xr < (r / 2)) && (x < ((r * r) / 2))) */
		  xr /= r;
		  /* ((xr == (x / (r * r))) && (xr < 0.5)) */
		  r *= r;
		  /* ((xr == (x / r)) && (x < (r / 2))) */
		  n += n;
		}
	      /* ((xr >= (r / 2)) && (xr < 0.5)) */
	      x = xr;
	      e -= n;
	    }
	  else
	    {
	      x *= 2;
	      e -= 1;
	      break;
	    }
	}
    }
  (*eptr) = e;
  return ((value < 0) ? (-x) : x);
}

double
ldexp (double value, int exponent)
{
  double x = value;
  int e = exponent;
  double r = 2;
  if (e > 0)
    {
      if (e == 1)
	return (x * 2);
      while (1)
	{
	  if ((e % 2) != 0)
	    x *= r;
	  e /= 2;
	  if (e == 1)
	    return (x * r * r);
	  r *= r;
	}
    }
  else if (e < 0)
    {
      e = (-e);
      if (e == 1)
	return (x / 2);
      while (1)
	{
	  if ((e % 2) != 0)
	    x /= r;
	  e /= 2;
	  if (e == 1)
	    return ((x / r) / r);
	  r *= r;
	}
    }
  else
    return (x);
}

#endif /* not HAVE_FREXP */

#ifndef HAVE_MODF

double
modf (double value, double * iptr)
{
  int exponent;
  double significand = (frexp (value, (&exponent)));
  if ((significand == 0) || (exponent <= 0))
    {
      (*iptr) = 0;
      return (value);
    }
  {
    double s =
      ((((significand < 0) ? (-significand) : significand) * 2) - 1);
    int e = (exponent - 1);
    double n = 1;
    while (1)
      {
	if (e == 0)
	  break;
	s *= 2;
	e -= 1;
	n *= 2;
	if (s >= 1)
	  {
	    s -= 1;
	    n += 1;
	    if (s <= 0)
	      {
		/* Multiply n by 2^e */
		double b = 2;
		if (e == 0)
		  break;
		while (1)
		  {
		    if ((e % 2) == 1)
		      {
			n *= b;
			if (e == 1)
			  break;
			e -= 1;
		      }
		    b *= b;
		    e /= 2;
		  }
		break;
	      }
	  }
      }
    if (significand < 0)
    {
      (*iptr) = (- n);
      return (- s);
    }
    else
    {
      (*iptr) = n;
      return (s);
    }
  }
}

#endif /* not HAVE_MODF */

#ifndef HAVE_FLOOR

double
floor (double x)
{
  double iptr;
  double fraction = (modf (x, (&iptr)));
  return ((fraction < 0) ? (iptr - 1) : iptr);
}

double
ceil (double x)
{
  double iptr;
  double fraction = (modf (x, (&iptr)));
  return ((fraction > 0) ? (iptr + 1) : iptr);
}

#endif /* not HAVE_FLOOR */

#ifdef DEBUG_MISSING

main ()
{
  double input;
  double output;
  int exponent;
  while (1)
    {
      printf ("Number -> ");
      scanf ("%F", (&input));
      output = (frexp (input, (&exponent)));
      printf ("Input = %G; Output = %G; Exponent = %d\n",
	      input, output, exponent);
      printf ("Result = %G\n", (ldexp (output, exponent)));
    }
}

#endif /* DEBUG_MISSING */
