1 files changed, 89 insertions, 0 deletions
diff --git a/6/2.c b/6/2.c
new file mode 100644
index 0000000..c9d1083
--- /dev/null
+++ b/6/2.c
@@ -0,0 +1,89 @@
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+enum {
+	WIDTH = 1000,
+	HEIGHT = 1000,
+};
+
+struct instr {
+	signed char db;
+	struct pos {
+		unsigned short x, y;
+	} start, end;
+};
+
+unsigned short read_be16(void *_buf)
+{
+	unsigned char *buf = _buf;
+	return (buf[0] << 8) | buf[1];
+}
+
+bool read_instr(struct instr *i, FILE *f)
+{
+	unsigned char buf[9];
+	signed char db;
+	unsigned short v;
+
+	assert(i != NULL);
+	assert(f != NULL);
+
+	if (fread(buf, sizeof buf, 1, f) != 1)
+		return false;
+	if (buf[0] <= 127)
+		db = buf[0];
+	else {
+		db = -0x80;
+		db += buf[0] - 0x80;
+	}
+	if (db < -1 || db > 2) {
+		fprintf(stderr, "this db is crazy: %d -> %d\n", buf[0], db);
+		return false;
+	}
+	i->db = db;
+
+#define SET(f, p) { \
+		v = read_be16(&buf[p]); \
+		if (v > 999) \
+			return false; \
+		i->f = v; \
+	}
+	SET(start.x, 1);
+	SET(start.y, 3);
+	SET(end.x, 5);
+	SET(end.y, 7);
+
+	return true;
+}
+
+int main(void)
+{
+	int screen[WIDTH][HEIGHT] = { 0 };
+	unsigned long long total;
+	struct instr i;
+	FILE *f;
+
+	f = fopen("inputbin", "rb");
+	if (f == NULL)
+		exit(EXIT_FAILURE);
+
+	while (read_instr(&i, f)) {
+		for (int y = i.start.y; y <= i.end.y; y++) {
+			for (int x = i.start.x; x <= i.end.x; x++) {
+				screen[x][y] += i.db;
+				if (screen[x][y] < 0)
+					screen[x][y] = 0;
+			}
+		}
+	}
+
+	fclose(f);
+
+	total = 0;
+	for (int y = 0; y < HEIGHT; y++)
+		for (int x = 0; x < WIDTH; x++)
+			total += screen[x][y];
+	printf("%llu\n", total);
+}