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frexpl.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*                  Copyright (c) 1985-2005 AT&T Corp.                  *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                            by AT&T Corp.                             *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#pragma prototyped

/*
 * frexpl/ldexpl implementation
 */

#include <ast.h>

#include "FEATURE/float"

#if _lib_frexpl && _lib_ldexpl

NoN(frexpl)

#else

#ifndef LDBL_MAX_EXP
#define LDBL_MAX_EXP    DBL_MAX_EXP
#endif

#if defined(_ast_fltmax_exp_index) && defined(_ast_fltmax_exp_shift)

#define INIT()          _ast_fltmax_exp_t _pow_
#define pow2(i)         (_pow_.f=1,_pow_.e[_ast_fltmax_exp_index]+=((i)<<_ast_fltmax_exp_shift),_pow_.f)

#else

static _ast_fltmax_t    pow2tab[LDBL_MAX_EXP + 1];

static int
init(void)
{
      register int            x;
      _ast_fltmax_t           g;

      g = 1;
      for (x = 0; x < elementsof(pow2tab); x++)
      {
            pow2tab[x] = g;
            g *= 2;
      }
      return 0;
}

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

#define pow2(i)         (pow2tab[i])

#endif

#if !_lib_frexpl

#undef      frexpl

extern _ast_fltmax_t
frexpl(_ast_fltmax_t f, int* p)
{
      register int            k;
      register int            x;
      _ast_fltmax_t           g;

      INIT();

      /*
       * normalize
       */

      x = k = LDBL_MAX_EXP / 2;
      if (f < 1)
      {
            g = 1.0L / f;
            for (;;)
            {
                  k = (k + 1) / 2;
                  if (g < pow2(x))
                        x -= k;
                  else if (k == 1 && g < pow2(x+1))
                        break;
                  else
                        x += k;
            }
            if (g == pow2(x))
                  x--;
            x = -x;
      }
      else if (f > 1)
      {
            for (;;)
            {
                  k = (k + 1) / 2;
                  if (f > pow2(x))
                        x += k;
                  else if (k == 1 && f > pow2(x-1))
                        break;
                  else
                        x -= k;
            }
            if (f == pow2(x))
                  x++;
      }
      else
            x = 1;
      *p = x;

      /*
       * shift
       */

      x = -x;
      if (x < 0)
            f /= pow2(-x);
      else if (x < LDBL_MAX_EXP)
            f *= pow2(x);
      else
            f = (f * pow2(LDBL_MAX_EXP - 1)) * pow2(x - (LDBL_MAX_EXP - 1));
      return f;
}

#endif

#if !_lib_ldexpl

#undef      ldexpl

extern _ast_fltmax_t
ldexpl(_ast_fltmax_t f, register int x)
{
      INIT();
      if (x < 0)
            f /= pow2(-x);
      else if (x < LDBL_MAX_EXP)
            f *= pow2(x);
      else
            f = (f * pow2(LDBL_MAX_EXP - 1)) * pow2(x - (LDBL_MAX_EXP - 1));
      return f;
}

#endif

#endif

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