うんこーどだけどどこかで役に立つかも…立たないか(´д｀)
【追記】使う度にfifo_init()する仕様です、さーせんm(__)m
tinyfifo.c
/* Tiny FIFO */

#include <stdio.h>

#define		TINY_FIFO_SIZE		5

typedef		unsigned char		fifo_t;

typedef enum tiny_fifo_code {
	FIFO_COMPLETE,
	FIFO_ERROR
} fifo_e;

static struct s_tiny_fifo_cntx {
	fifo_t		buff[TINY_FIFO_SIZE];
	int			count;
	int			length;
} tiny_fifo;

static void fifo_init(void)
{
	tiny_fifo.count = 0;
	tiny_fifo.length = 0;
}

static int fifo_count(void)
{
	return tiny_fifo.length - tiny_fifo.count;
}

static fifo_e fifo_set(fifo_t x)
{
	fifo_e result = FIFO_ERROR;

	if (tiny_fifo.length < TINY_FIFO_SIZE) {
		tiny_fifo.buff[tiny_fifo.length++] = x;
		result = FIFO_COMPLETE;
	}

	return result;
}

static fifo_e fifo_get(fifo_t *x)
{
	fifo_e result = FIFO_ERROR;

	if (x != NULL) {
		if (tiny_fifo.count < tiny_fifo.length) {
			*x = tiny_fifo.buff[tiny_fifo.count++];
			result = FIFO_COMPLETE;
		}
	}

	return result;
}

/* for TEST */

static fifo_e fifo_set_(fifo_t x)
{
	fifo_e result = fifo_set(x);
	if (result == FIFO_COMPLETE) {
		printf("Set %d.\n", x);
	}
	else {
		printf("ERROR : Set %d.\n", x);
	}
	return result;
}

static fifo_e fifo_get_(fifo_t *x)
{
	fifo_e result = fifo_get(x);
	if (result == FIFO_COMPLETE) {
		printf("Get %d.\n", *x);
	}
	else {
		printf("ERROR : Get.\n");
	}
	return result;
}

int main(int argc, char* argv[])
{
	fifo_t x;
	fifo_init();
	fifo_set_(1);
	fifo_set_(3);
	fifo_get_(&x);
	fifo_set_(8);
	fifo_set_(9);
	fifo_set_(2);
	fifo_set_(6);
	while (fifo_count()) {
		fifo_get_(&x);
	}
	fifo_get_(&x);
	getchar();
	return 0;
}