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    /* vim: set tabstop=4 expandtab shiftwidth=4 softtabstop=4: */
    
    /*
     * Copyright 2015 University of Piemonte Orientale, Computer Science Institute
     *
     * This file is part of UPOalglib.
     *
     * UPOalglib 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.
     *
     * UPOalglib 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 UPOalglib.  If not, see <http://www.gnu.org/licenses/>.
     */
    
    #include "stack_private.h"
    #include <stdio.h>
    #include <stdlib.h>
    
    
    upo_stack_t upo_stack_create()
    {
        upo_stack_t stack = malloc(sizeof(struct upo_stack_s));
        if (stack == NULL)
        {
            perror("Unable to create a stack");
            abort();
        }
    
        stack->top = NULL;
        stack->size = 0;
    
        return stack;
    }
    
    void upo_stack_destroy(upo_stack_t stack, int destroy_data)
    {
        if (stack != NULL)
        {
            upo_stack_clear(stack, destroy_data);
            free(stack);
        }
    }
    
    void upo_stack_push(upo_stack_t stack, void *data)
    {
        if (stack) {
            upo_stack_node_t *second = stack->top;
    
            upo_stack_node_t *first = malloc(sizeof(upo_stack_node_t));
            first->data = data;
            first->next = second;
    
            stack->top = first;
            ++stack->size;
        }
    }
    
    void upo_stack_pop(upo_stack_t stack, int destroy_data)
    {
        if (stack) {
            upo_stack_node_t *first = stack->top->next;
            if (destroy_data) {
                free(stack->top->data);
            }
            free(stack->top);
            stack->top = first;
            --stack->size;
        }
    }
    
    void* upo_stack_top(const upo_stack_t stack)
    {
        return !upo_stack_is_empty(stack) ? stack->top->data : NULL;
    }
    
    int upo_stack_is_empty(const upo_stack_t stack)
    {
        return stack ? stack->size == 0 : 1;
    }
    
    size_t upo_stack_size(const upo_stack_t stack)
    {
        return stack ? stack->size : 0;
    }
    
    void upo_stack_clear(upo_stack_t stack, int destroy_data)
    {
        while (!upo_stack_is_empty(stack)) {
            upo_stack_pop(stack, destroy_data);
        }
    }