/*

 * stack.c -- Implementation for stack functions for use by extensions.

 */

/*

 * Copyright (C) 2012, 2013 the Free Software Foundation, Inc.

 *

 * This file is part of GAWK, the GNU implementation of the

 * AWK Programming Language.

 *

 * GAWK 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 3 of the License, or

 * (at your option) any later version.

 *

 * GAWK 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 this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA

 */

#include <stdlib.h>

#include "stack.h"

#define INITIAL_STACK	20

static size_t size;

static void **stack;

static int index = -1;

/* stack_empty --- return true if stack is empty */

int

stack_empty()

{

	return index < 0;

}

/* stack_top --- return top object on the stack */

void *

stack_top()

{

	if (stack_empty() || stack == NULL)

		return NULL;

	return stack[index];

}

/* stack_pop --- pop top object and return it */

void *

stack_pop()

{

	if (stack_empty() || stack == NULL)

		return NULL;

	return stack[index--];

}

/* stack_push --- push an object onto the stack */

int stack_push(void *object)

{

	void **new_stack;

	size_t new_size = 2 * size;

	if (stack == NULL) {

		stack = (void **) malloc(INITIAL_STACK * sizeof(void *));

		if (stack == NULL)

			return 0;

		size = INITIAL_STACK;

	} else if (index + 1 >= size) {

		if (new_size < size)

			return 0;

		new_stack = realloc(stack, new_size * sizeof(void *));

		if (new_stack == NULL)

			return 0;

		size = new_size;

		stack = new_stack;

	}

	stack[++index] = object;

	return 1;

}