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optctx.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*          Copyright (c) 1985-2010 AT&T Intellectual Property          *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                    by AT&T Intellectual Property                     *
*                                                                      *
*                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
/*
 * Glenn Fowler
 * AT&T Research
 *
 * _opt_infop_ context control
 *
 * allocate new context:
 *    new_context = optctx(0, 0);
 * free new context:
 *    optctx(0, new_context);
 * switch to new_context:
 *    old_context = optctx(new_context, 0);
 * switch to old_context and free new_context:
 *    optctx(old_context, new_context);
 */

#include <optlib.h>

static Opt_t*     freecontext;

Opt_t*
optctx(Opt_t* p, Opt_t* o)
{
      if (o)
      {
            if (freecontext)
                  free(o);
            else
                  freecontext = o;
            if (!p)
                  return 0;
      }
      if (p)
      {
            o = _opt_infop_;
            _opt_infop_ = p;
      }
      else
      {
            if (o = freecontext)
                  freecontext = 0;
            else if (!(o = newof(0, Opt_t, 1, 0)))
                  return 0;
            memset(o, 0, sizeof(Opt_t));
            o->state = _opt_infop_->state;
      }
      return o;
}

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