fifo.c

#include <stdio.h>
#include <stdlib.h>

#define FIFO_SIZE 42

typedef struct
{
	int x, y;
}
pair;

pair fifo[FIFO_SIZE];
int fifo_read_pointer = 0;
int fifo_write_pointer = 0;

void fatal_error (char *msg)
{
	fprintf (stderr, "%s\n", msg);
	exit (1);
}

void push_pair (int x, int y)
{
	if (fifo_write_pointer < 0 || fifo_write_pointer >= FIFO_SIZE)
		fatal_error ("push_pair: fifo inconsistence");
	else
	{
		printf ("pushing (%d,%d)\n", x, y);
		fifo[fifo_write_pointer].x = x;
		fifo[fifo_write_pointer].y = y;
		fifo_write_pointer++;
		if (fifo_write_pointer >= FIFO_SIZE)
			fifo_write_pointer = 0;
		if (fifo_write_pointer == fifo_read_pointer)
			fatal_error ("fifo overflow");
    }
}

pair pop_pair (void)
{
	pair nix;
	if (fifo_read_pointer < 0 || fifo_read_pointer >= FIFO_SIZE)
    {
		fatal_error ("pop_pair: fifo inconsistence");		
		return nix;
    }
	else if (fifo_read_pointer == fifo_write_pointer)
    {
		fatal_error ("fifo underflow");
		return nix;
    }
	else
    {
		printf ("popping (%d,%d)\n", fifo[fifo_read_pointer].x, fifo[fifo_read_pointer].y);
		pair value = fifo[fifo_read_pointer];
		fifo[fifo_read_pointer].x = 0;
		fifo[fifo_read_pointer].y = 0;
		fifo_read_pointer++;
		if (fifo_read_pointer >= FIFO_SIZE)
			fifo_read_pointer = 0;
		return value;
    }
}

void dump_stack (void)
{
	int i;
	printf ("dump_stack:");
	for (i = 0; i < FIFO_SIZE; i++)
		printf (" (%d,%d)", fifo[i].x, fifo[i].y);
	printf ("\n");
}

int main (void)
{
	dump_stack ();
	push_pair (3, 0);
	dump_stack ();
	push_pair (7, 2);
	dump_stack ();
	push_pair (23, 23);
	dump_stack ();
	pop_pair ();
	dump_stack ();
	pop_pair ();
	dump_stack ();
	push_pair (42, 137);
	dump_stack ();
	pop_pair ();
	dump_stack ();
	pop_pair ();
	dump_stack ();
	return 0;
}