/** SFSEXP: Small, Fast S-Expression Library version 1.0Written by Matthew Sottile (matt@lanl.gov)Copyright (2004). The Regents of the University of California. This materialwas produced under U.S. Government contract W-7405-ENG-36 for Los AlamosNational Laboratory, which is operated by the University of California forthe U.S. Department of Energy. The U.S. Government has rights to use,reproduce, and distribute this software. NEITHER THE GOVERNMENT NOR THEUNIVERSITY MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY LIABILITYFOR THE USE OF THIS SOFTWARE. If software is modified to produce derivativeworks, such modified software should be clearly marked, so as not to confuseit with the version available from LANL.Additionally, this program is free software; you can redistribute it and/ormodify it under the terms of the GNU General Public License as published bythe Free Software Foundation; either version 2 of the License, or (at youroption) any later version. Accordingly, this program is distributed in thehope that it will be useful, but WITHOUT ANY WARRANTY; without even theimplied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Seethe GNU General Public License for more details.LA-CC-04-094**//** * \file faststack.h * * \brief Implementation of a fast stack with smart memory management. * * Author: Matt Sottile (matt@lanl.gov) * See LICENSE for info on licensing. */#ifndef __FASTSTACK_H__#define __FASTSTACK_H__#ifdef _DEBUG_MALLOCS_#include "malloc_util.h"#endif/** * Structure representing a single level in the stack.  Has a pointer to the * level above and below itself and a pointer to a generic blob of data * associated with this level. */typedef struct stack_level {  /**   * Pointer to the level above this one.  If NULL, then this level is the   * top of the stack.  If above is non-NULL, this level *may* be the top,   * but all that can be guaranteed is that there are other allocated   * but potentially unused levels above this one.   */  struct stack_level *above;  /**   * Pointer to the level below this one.  If NULL, then this level is the   * bottom.   */  struct stack_level *below;  /**   * Pointer to some data associated with this level.  User is responsible   * for knowing what to cast the \c void \c * pointer into.   */  void *data;} stack_lvl_t;/** * Wrapper around the stack levels - keeps a pointer to the current top and * bottom of the stack and a count of the current height.  This allows the top * to have non-null above pointer resulting from previously allocated stack * levels that may be recycled later without \c malloc overhead. */typedef struct stack_wrapper {  /**   * The top of the stack.  If this is NULL, the stack is empty.   */  stack_lvl_t *top;    /**   * The bottom of the stack.  If this is NULL, the stack is empty.   */  stack_lvl_t *bottom;  /**   * The current height of the stack, in terms of allocated and used levels.   */  int height;} faststack_t;/** functions **//* this is for C++ */#ifdef __cplusplusextern "C" {#endif  /**   * Return a pointer to an empty stack structure.   */faststack_t *make_stack();  /**   * Given a stack structure, destroy it and free all of the stack levels.   * <B>Important note</B> : This function <I>does not</I> free the data   * pointed to from each level of the stack - the user is responsible   * for freeing this data themselves before calling this function to   * prevent memory leakage.   */void destroy_stack(faststack_t *s);  /**   * Given a stack, push a new level on referring to the data pointer.   */faststack_t *push(faststack_t *cur_stack, void *data);  /**   * Given a stack, pop a level off and return a pointer to that level.   * The user is responsible for extracting the data, but the stack_lvl_t   * structures pointed to from the level (above and below) should be left   * alone.   */stack_lvl_t *pop(faststack_t *s);/* this is for C++ */#ifdef __cplusplus}#endif/** * Given a stack \a s, examine the data pointer at the top. */#define top_data(s) (s->top->data)/** * Given a stack \a s, check to see if the stack is empty or not.  Value * is boolean true or false. */#define empty_stack(s) (s->top == NULL)#endif /* __FASTSTACK_H__ */