/*--------------------------------------------------------------------*/
/* stack.c (Version 2)                                                */
/* 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;
};

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

struct Stack *Stack_new(void)

/* Return a new Stack. */

{
   struct Stack *psStack;

   psStack = (struct Stack *)malloc(sizeof(struct Stack));
   assert(psStack != NULL);

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

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

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

void Stack_free(struct Stack *psStack)

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

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

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

static void Stack_grow(struct Stack *psStack)

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

{
   assert(psStack != NULL);

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

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

void Stack_push(struct Stack *psStack, double dItem)

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

{
   assert(psStack != NULL);

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

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

double Stack_top(struct Stack *psStack)

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

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

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

void Stack_pop(struct Stack *psStack)

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

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

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

int Stack_isEmpty(struct Stack *psStack)

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

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