/*--------------------------------------------------------------------*/
/* stack.c (Version 3)                                                */
/* Author: Bob Dondero                                                */
/*--------------------------------------------------------------------*/

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

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

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

/* A Stack consists of an array of items, and related data. */

struct Stack
{
   /* The array in which items are stored. */
   double *pdArray;

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

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

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

Stack_T Stack_new(void)

/* Return a new Stack_T. */

{
   Stack_T oStack;

   oStack = (Stack_T)malloc(sizeof(struct Stack));
   assert(oStack != NULL);

   oStack->pdArray =
      (double*)calloc(INITIAL_PHYS_LENGTH, sizeof(double));
   assert(oStack->pdArray != NULL);

   oStack->iTop = 0;
   oStack->iPhysLength = INITIAL_PHYS_LENGTH;
   return oStack;
}

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

void Stack_free(Stack_T oStack)

/* Free oStack.  Do nothing if oStack is NULL. */

{
   if (oStack == NULL) return;
   free(oStack->pdArray);
   free(oStack);
}

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

static void Stack_grow(Stack_T oStack)

/* Double the physical length of oStack. */

{
   assert(oStack != NULL);

   oStack->iPhysLength *= GROWTH_FACTOR;
   oStack->pdArray =
      (double*)realloc(oStack->pdArray,
                       sizeof(double) * oStack->iPhysLength);
   assert(oStack->pdArray != NULL);
}

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

void Stack_push(Stack_T oStack, double dItem)

/* Push dItem onto oStack.
   It is a checked runtime error for oStack to be NULL. */

{
   assert(oStack != NULL);

   if (oStack->iTop == oStack->iPhysLength)
      Stack_grow(oStack);
   (oStack->pdArray)[oStack->iTop] = dItem;
   (oStack->iTop)++;
}

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

double Stack_top(Stack_T oStack)

/* Return the top item of oStack.
   It is a checked runtime error for oStack to be NULL or empty. */

{
   assert(oStack != NULL);
   assert(oStack->iTop > 0);
   return (oStack->pdArray)[oStack->iTop - 1];
}

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

void Stack_pop(Stack_T oStack)

/* Pop oStack, and discard the popped item.
   It is a checked runtime error for oStack to be NULL or empty. */

{
   assert(oStack != NULL);
   assert(oStack->iTop > 0);
   (oStack->iTop)--;
}

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

int Stack_isEmpty(Stack_T oStack)

/* Return 1 (TRUE) iff oStack is empty.
   It is a checked runtime error for oStack to be NULL. */

{
   assert(oStack != NULL);
   return oStack->iTop == 0;
}