/*------------------------------------------------------------------*/
/* stackarrayao.c                                                   */
/* Author: Bob Dondero                                              */
/* A Stack abstract object implementation as an array               */
/*------------------------------------------------------------------*/

#include "stackao.h"
#include <stdlib.h>
#include <assert.h>

enum {INITIAL_PHYS_LENGTH = 2};
enum {GROWTH_FACTOR = 2};

/*------------------------------------------------------------------*/

/* The state of the Stack */

/* The array in which items are stored. */
static double *pdArray;

/* The index one beyond the top element. */
static int iTop;

/* The number of elements in the array. */
static int iPhysLength;

/* Is the Stack initialized? */
static int iInitialized = 0;

/*------------------------------------------------------------------*/

void Stack_init(void)

/* Initialize the Stack.
   It is a checked runtime error for the Stack to be initialized. */

{
   assert(! iInitialized);
   pdArray = (double*)calloc(INITIAL_PHYS_LENGTH, sizeof(double));
   assert(pdArray != NULL);
   iTop = 0;
   iPhysLength = INITIAL_PHYS_LENGTH;
   iInitialized = 1;
}

/*------------------------------------------------------------------*/

void Stack_free(void)

/* Free the resources consumed by the Stack.
   It is a checked runtime error for the Stack to be uninitialized. */

{
   assert(iInitialized);
   free(pdArray);
   iInitialized = 0;
}

/*------------------------------------------------------------------*/

static void Stack_grow(void)

/* Double the physical length of the Stack. */

{
   assert(iInitialized);
   iPhysLength *= GROWTH_FACTOR;
   pdArray = (double*)realloc(pdArray, sizeof(double) * iPhysLength);
   assert(pdArray != NULL);
}

/*------------------------------------------------------------------*/

void Stack_push(double dItem)

/* Push dItem onto the Stack.
   It is a checked runtime error for the Stack to be uninitialized. */

{
   assert(iInitialized);

   if (iTop == iPhysLength)
      Stack_grow();

   pdArray[iTop] = dItem;
   iTop++;
}

/*------------------------------------------------------------------*/

double Stack_pop(void)

/* Pop the Stack, and return the popped item.
   It is a checked runtime error for the Stack to be uninitialized or
   empty. */

{
   assert(iInitialized);
   assert(iTop > 0);
   iTop--;
   return pdArray[iTop];
}

/*------------------------------------------------------------------*/

int Stack_isEmpty(void)

/* Return 1 (TRUE) iff the Stack is empty.
   It is a checked runtime error for the Stack to be uninitialized. */

{
   assert(iInitialized);
   return iTop == 0;
}