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GitHub Repository: att/ast
 Path: blob/master/src/lib/libast/comp/frexp.c
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/***********************************************************************

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*                                                                      *

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*               This software is part of the ast package               *

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*          Copyright (c) 1985-2011 AT&T Intellectual Property          *

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*                      and is licensed under the                       *

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*                 Eclipse Public License, Version 1.0                  *

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*                    by AT&T Intellectual Property                     *

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*                                                                      *

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*                A copy of the License is available at                 *

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*          http://www.eclipse.org/org/documents/epl-v10.html           *

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*         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *

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*                                                                      *

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*              Information and Software Systems Research               *

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*                            AT&T Research                             *

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*                           Florham Park NJ                            *

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*                                                                      *

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*                 Glenn Fowler <[email protected]>                  *

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*                  David Korn <[email protected]>                   *

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*                   Phong Vo <[email protected]>                    *

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*                                                                      *

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***********************************************************************/

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#pragma prototyped

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/*

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 * frexp/ldexp implementation

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 */

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#include <ast.h>

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#include "FEATURE/float"

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#if _lib_frexp && _lib_ldexp

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NoN(frexp)

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#else

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#if defined(_ast_dbl_exp_index) && defined(_ast_dbl_exp_shift)

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#define INIT()		_ast_dbl_exp_t _pow_

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#define pow2(i)		(_pow_.f=1,_pow_.e[_ast_dbl_exp_index]+=((i)<<_ast_dbl_exp_shift),_pow_.f)

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#else

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static double		pow2tab[DBL_MAX_EXP + 1];

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static int

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init(void)

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{

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	register int	x;

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	double		g;

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	g = 1;

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	for (x = 0; x < elementsof(pow2tab); x++)

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	{

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		pow2tab[x] = g;

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		g *= 2;

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	}

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	return 0;

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}

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#define INIT()		(pow2tab[0]?0:init())

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#define pow2(i)		pow2tab[i]

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#endif

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#if !_lib_frexp

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extern double

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frexp(double f, int* p)

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{

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	register int	k;

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	register int	x;

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	double		g;

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	INIT();

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	/*

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	 * normalize

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	 */

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	x = k = DBL_MAX_EXP / 2;

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	if (f < 1)

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	{

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		g = 1.0L / f;

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		for (;;)

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		{

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			k = (k + 1) / 2;

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			if (g < pow2(x))

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				x -= k;

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			else if (k == 1 && g < pow2(x+1))

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				break;

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			else

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				x += k;

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		}

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		if (g == pow2(x))

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			x--;

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		x = -x;

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	}

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	else if (f > 1)

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	{

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		for (;;)

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		{

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			k = (k + 1) / 2;

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			if (f > pow2(x))

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				x += k;

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			else if (k == 1 && f > pow2(x-1))

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				break;

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			else

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				x -= k;

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		}

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		if (f == pow2(x))

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			x++;

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	}

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	else

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		x = 1;

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	*p = x;

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	/*

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	 * shift

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	 */

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	x = -x;

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	if (x < 0)

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		f /= pow2(-x);

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	else if (x < DBL_MAX_EXP)

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		f *= pow2(x);

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	else

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		f = (f * pow2(DBL_MAX_EXP - 1)) * pow2(x - (DBL_MAX_EXP - 1));

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	return f;

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}

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#endif

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#if !_lib_ldexp

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extern double

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ldexp(double f, register int x)

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{

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	INIT();

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	if (x < 0)

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		f /= pow2(-x);

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	else if (x < DBL_MAX_EXP)

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		f *= pow2(x);

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	else

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		f = (f * pow2(DBL_MAX_EXP - 1)) * pow2(x - (DBL_MAX_EXP - 1));

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	return f;

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}

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#endif

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#endif

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