add function for computing the bytesize of the *.mcX file

src/dat/mcx.c

@@ -28,6 +28,15 @@ void mcx_delchunk(u8 *restrict buf, int chunk) {
 	memmove(head, tail, blen);
 }
 
+/* Sum together the 4th byte in each location integer to compute the sector size of all chunks.
+ * Multiplying by `0x1000`, and adding the size of the table itself. */
+size_t mcx_calcsize(const u8 *restrict buf) {
+	size_t size = 0;
+	for (uint i = 0; i < 0x400; i++)
+		size += *(buf + (i * 4) + 3);
+	return (size * 0x1000) + 0x2000;
+}
+
 /* an `*.mcX` contains a `0x2000` byte long table, the first `0x1000` containing
  * `0x400` entries of chunk data.
  * This chunk data is big-endian, where bytes `0xFFFFFF00` represent the `0x1000` sector offset.

src/dat/mcx.h

@@ -18,6 +18,9 @@ struct mcx_chunk {
 /* Deletes chunk `idx` from `buf`, moving all chunks downwards in the process. */
 void mcx_delchunk(u8 *restrict buf, int idx);
 
+/* Computes the byte size of the `*.mcX` file in `buf` and returns it. */
+size_t mcx_calcsize(const u8 *restrict buf) NONNULL((1)) PURE;
+
 /* indexes the chunks in an `*.mcX` file, writing `0x400` of entries to `chunks` */
 void mcx_index(const u8 *restrict buf, struct mcx_chunk *restrict chunks) NONNULL((1, 2));