1 files changed, 68 insertions, 0 deletions
diff --git a/user/deflate.c b/user/deflate.c
new file mode 100644
index 0000000..35018d0
--- /dev/null
+++ b/user/deflate.c
@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+int main(int argc, char **argv)
+{
+	FILE *in, *out;
+	int length_bytes = 0, length = 0, tracking = EOF, next;
+
+	if (argc != 3) {
+		fprintf(stderr, "usage: deflate in out\n");
+		return 1;
+	}
+
+	in = fopen(argv[1], "rb");
+	if (in == NULL) {
+		fprintf(stderr, "cannot read: %s\n", argv[1]);
+		return 1;
+	}
+
+	out = fopen(argv[2], "wb");
+	if (out == NULL) {
+		fprintf(stderr, "cannot write %s\n", argv[2]);
+		return 1;
+	}
+
+	while (next = getc(in), next != EOF) {
+		int diff;
+
+		if (tracking == EOF) {
+			tracking = next;
+			length = 1;
+			length_bytes = 0;
+			continue;
+		}
+
+		diff = tracking - next;
+		diff = diff < 1 ? -diff : diff;
+		if (diff < 2)
+			next = tracking;
+
+		if (tracking == next) {
+			length++;
+			if (length == 255) {
+				length_bytes++;
+				length = 0;
+			}
+			continue;
+		}
+
+		// write output
+		for (int i = 0; i < length_bytes; i++)
+			putc(255, out);
+		putc(length, out);
+		putc(tracking, out);
+		tracking = next;
+		length = 1;
+		length_bytes = 0;
+	}
+
+	if (length) {
+		for (int i = 0; i < length_bytes; i++)
+			putc(255, out);
+		putc(length, out);
+		putc(tracking, out);
+	}
+
+	return 0;
+}