rle.c

#include <stdio.h>
#include <limits.h>

int
rle_encode(FILE *src, FILE *dest) {
	int c, prev, cnt;

	prev = fgetc(src);
	cnt = 1;

	while (prev != EOF) {
		c = fgetc(src);

		if (c != prev || cnt == UCHAR_MAX) {
			fputc(cnt, dest);
			fputc(prev, dest);
			prev = c;
			cnt = 0;
		}

		cnt++;
	}

	return ferror(src);
}

int
rle_decode(FILE *src, FILE *dest) {
	int c, cnt, i;

	while ((cnt = fgetc(src)) != EOF && (c = fgetc(src)) != EOF)
		for (i = 0; i < cnt; i++)
			fputc(c, dest);

	return ferror(src);
}