/*
 * stack_template.c - A type-independent template for a single stack.
 * Samuel A. Rebelsky
 * Version 1.0 of 11 February 2007
 *
 * Note: To use this, you must define SPREFIX(thing), STYPE, and, optionaly,
 *   INITIAL_STACK_SIZE
 */

#include <stdlib.h>

#ifndef INITIAL_STACK_SIZE
#define INITIAL_STACK_SIZE 16
#endif 

#define _S_STACK SPREFIX(stack)
#define _S_TOP SPREFIX(top)
#define _S_SIZE SPREFIX(size)

/* Sam believes in stacks that can grow. */
STYPE *_S_STACK = NULL;	/* The stack. */
int _S_TOP = 0;		/* The top of the stack. */
int _S_SIZE = 0;		/* The current size of the stack. */

void 
SPREFIX(push)(STYPE val)
{
  /* If no stack exists, create one. */
  if (NULL == _S_STACK) {
    _S_SIZE = INITIAL_STACK_SIZE;
    _S_STACK = (STYPE *) malloc(_S_SIZE * sizeof(STYPE));
    _S_TOP = 0;
  }
  /* If the stack is too small, expand it. */
  if (_S_SIZE == _S_TOP) {
    STYPE *newstack = (STYPE *) malloc(2*_S_SIZE*sizeof(STYPE));
    /* WARNING! Did not check whether the result is null. */
    int i;
    for (i = 0; i < _S_SIZE; i++) {
      newstack[i] = _S_STACK[i];
    }
    free(_S_STACK);
    _S_STACK = newstack;
    _S_SIZE = 2*_S_SIZE;
  }
  /* We're FINALLY ready to push the value. */
  _S_STACK[_S_TOP++] = val;
} /* push(int) */

STYPE SPREFIX(pop)()
{
  return _S_STACK[--_S_TOP];
} /* pop() */

STYPE SPREFIX(empty)()
{
  return !_S_TOP;
} /* empty() */

#undef _S_STACK 
#undef _S_TOP 
#undef _S_SIZE