write function for bulk removal of chunks

src/dat/mcx.c

@@ -1,6 +1,6 @@
 #include "mcx.h"
 
-#include <assert.h>
+#include <endian.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
@@ -9,70 +9,35 @@
 #include "../util/compat/endian.h"
 #include "../util/intdef.h"
 
-/* Moves chunks `src_s` to `src_e` (inclusive) from `src`, back onto `dst`. */
-static void mvchunks(u8 *restrict buf, u8 *src, u8 *dst, int src_s, int src_e) {
-	assert(src > dst);
-	u32 *table = (u32 *)buf;
-	size_t len = src - dst; // acquire the amount of bytes that we shall move
-	assert(len % 0x1000);
-
-	// count how many bytes we need to move, whilst updating location data
-	size_t blen = 0;
-	for (src_s++; src_s <= src_e; src_s++) {
-		blen += (be32toh(table[src_s]) & 0xFF) * 0x1000;
-		table[src_s] -= htobe32((len / 0x1000) << 8);
-	}
-	memmove(dst, src, blen);
-}
-
-/* Deletes chunk `sidx` by moving chunks up to `eidx` back over `sidx` in `buf`.
+/* Deletes chunk `sidx`, by moving chunks up to `eidx` back over `sidx` in `buf`.
  * `rmb` is an optional additional offset that can be applied, and signifies bytes already removed.
  * Returns the bytes removed by this function. */
 static size_t delchunk(u8 *restrict buf, size_t rmb, int sidx, int eidx) {
-	// load the table data
+	// load the table data, and clear it
 	u32 *table = (u32 *)buf;
 	size_t slen, bidx, blen;
-	slen = be32toh(table[sidx]) & 0xFF;          // acquire the sector length of the chunk
-	bidx = (be32toh(table[sidx]) >> 8) * 0x1000; // acquire and compute the byte offset the chunk starts at
-	blen = slen * 0x1000;                        // compute the byte length of the chunk
-
-	// reset the table data
+	slen = be32toh(table[sidx] & 0xFF);        // acquire the sector length of the chunk
+	bidx = be32toh(table[sidx] >> 8) * 0x1000; // acquire and compute the byte offset the chunk starts at
+	blen = slen * 0x1000;                      // compute the byte length of the chunk
 	table[sidx] = 0;
-	table[sidx + 0x400] = htobe32(time(NULL)); // assign the current time to the timestamp, for correctness  NOTE: might need to zero-out instead
+	table[sidx + 0x400] = time(NULL); // assign the current time to the timestamp, for correctness  NOTE: might need to zero-out instead
 
-	// move the succeeding chunks over the deleted chunk
 	u8 *dst = buf + bidx - rmb;
 	u8 *src = buf + bidx + blen;
-	mvchunks(buf, src, dst, sidx, eidx - 1);
-	return blen;
+	rmb = blen;
+	blen = 0;
+	for (sidx++; sidx < eidx; sidx++) {
+		blen += be32toh(table[sidx] & 0xFF) * 0x1000;
+		table[sidx] -= htobe32(slen << 8);
+	}
+	memmove(dst, src, blen);
+	return rmb;
 }
 
-/* Just call `delchunk` with the parameters and some defaults.
- * This is done instead of `delchunk` being globally linked, because
- * `delchunk` requests more specific parameters, which is confusing outside this module. */
 size_t mcx_delchunk(u8 *restrict buf, int chunk) {
 	return delchunk(buf, 0, chunk, 0x400);
 }
 
-size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) {
-	assert(start < end && end < 0x400);
-	u32 *table = (u32 *)buf;
-	u8 *dst = buf + (be32toh(table[start]) >> 8) * 0x1000;
-	u8 *src = buf + (be32toh(table[end]) >> 8) * 0x1000;
-	src += (be32toh(table[end]) & 0xFF) * 0x1000;
-
-	// zeroes-out the chunk data within this range. (and set the timestamp)
-	u32 ts = htobe32(time(NULL));
-	for (int i = start; i <= end; i++) {
-		table[i] = 0;
-		table[i + 0x400] = ts;
-	}
-
-	// move the remaining chunks down
-	mvchunks(buf, src, dst, start, end);
-	return src - dst;
-}
-
 /* comparer function for to be inputted into `qsort` to compare two */
 static int cmp_chunkids(const void *restrict x, const void *restrict y) {
 	u16 x2 = *(u16 *)x;
@@ -80,19 +45,16 @@ static int cmp_chunkids(const void *restrict x, const void *restrict y) {
 	return (x2 > y2) - (x2 < y2);
 }
 
-/* Sorts the chunks marked for deletion from smallest to greatest index.
- * Then performs the deletion in this order. Making sure to only update the chunks up to the next. */
-size_t mcx_delchunk_bulk(u8 *restrict buf, const u16 *restrict chunks, int chunkc) {
+void mcx_delchunks(u8 *restrict buf, const u16 *restrict chunks, int chunkc) {
 	// ensure the chunks ids we're working on are sorted from least to greatest
 	u16 chunkids[chunkc + 1];
 	memcpy(chunkids, chunks, chunkc);
 	qsort(chunkids, chunkc, sizeof(int), cmp_chunkids);
-	chunkids[chunkc] = 0x400; // set the spare chunk to the max chunks, so the rest of the chunks are moved
+	chunkids[chunkc] = 0; // set the spare chunk to zero, to prevent out-of-bounds access
 
 	size_t rmb = 0;
 	for (int i = 0; i < chunkc; i++)
 		rmb += delchunk(buf, rmb, chunkids[i], chunkids[i + 1]);
-	return rmb;
 }
 
 /* Sum together the 4th byte in each location integer to compute the sector size of all chunks.

src/dat/mcx.h

@@ -14,24 +14,12 @@ struct mcx_chunk {
 	u32 time;   // modification time in epoch seconds
 };
 
-/* Deletes a single chunk (`chunk`) out of `buf`.
- * The chunk's location data shall become `0`, and timestamp data the current time.
- * All succeeding chunks shall be moved back, freeing space.
- * Returns the amount of bytes removed. */
-size_t mcx_delchunk(u8 *restrict buf, int chunk) NONNULL((1));
+/* Deletes chunk `idx` from `buf`, moving all chunks downwards in the process. */
+size_t mcx_delchunk(u8 *restrict buf, int idx);
 
-/* Deletes the range defined by `start`—`end` (inclusive) of chunks out of `buf`.
- * The chunk's location data shall become `0`, and timestamp data the current time.
- * All succeeding chunks shall be moved back, freeing space.
- * Returns the amount of bytes removed */
-size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) NONNULL((1));
-
-/* Deletes a `chunkc` chunks from `chunks` out of `buf`.
- * If the `chunks` indices are known to be sequential, i.e. have a constant difference of `1`, `mcx_delchunk_range` should be preferred.
- * The chunk's location data shall become `0`, and timestamp data the current time.
- * All succeeding chunks shall be moved back, freeing space.
- * Returns the amount of bytes removed */
-size_t mcx_delchunk_bulk(u8 *restrict buf, const u16 *restrict chunks, int chunkc) NONNULL((1, 2));
+/* Deletes `chunkc` chunks specified in `chunks` from the `*.mcX` file.
+ * This is done in a way to perform minimal memmove operations. */
+void mcx_delchunks(u8 *restrict buf, const u16 *restrict chunks, int chunkc);
 
 /* Computes the byte size of the `*.mcX` file in `buf` and returns it. */
 size_t mcx_calcsize(const u8 *restrict buf) NONNULL((1)) PURE;