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refactor of mcx_delchunk to make things a bit more clear and flexible

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Quinn
2025-08-27 12:03:00 +02:00
parent 43e3e4fe85
commit 767f3a5c13
2 changed files with 23 additions and 17 deletions
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37
src/dat/mcx.c
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@@ -9,26 +9,33 @@
#include "../util/compat/endian.h"
#include "../util/intdef.h"
void mcx_delchunk(u8 *restrict buf, int chunk) {
/* 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, and clear it
u32 *table = (u32 *)buf;
size_t bidx = be32toh(table[chunk] >> 8) * 0x1000; // compute the byte offset the chunk starts at
size_t blen = be32toh(table[chunk] & 0xFF) * 0x1000; // compute the byte length of the chunk
size_t slen = be32toh(table[chunk] & 0xFF); // acquire the sector length of the chunk
table[chunk] = 0;
table[chunk + 0x400] = time(NULL); // assign the current time to the timestamp, for correctness NOTE: might need to zero-out instead
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
table[sidx] = 0;
table[sidx + 0x400] = time(NULL); // assign the current time to the timestamp, for correctness NOTE: might need to zero-out instead
// store the head and tail end of the current chunk
u8 *head = buf + bidx;
u8 *tail = buf + bidx + blen;
// count the amount of bytes that we must move
u8 *dst = buf + bidx - rmb;
u8 *src = buf + bidx + blen;
rmb = blen;
blen = 0;
for (chunk++; chunk < 0x400; chunk++) {
blen += table[chunk] & 0xFF * 0x1000;
table[chunk] -= htobe32(slen << 8);
for (sidx++; sidx < eidx; sidx++) {
blen += be32toh(table[sidx] & 0xFF) * 0x1000;
table[sidx] -= htobe32(slen << 8);
}
memmove(head, tail, blen);
memmove(dst, src, blen);
return rmb;
}
size_t mcx_delchunk(u8 *restrict buf, int chunk) {
return delchunk(buf, 0, chunk, 0x400);
}
/* Sum together the 4th byte in each location integer to compute the sector size of all chunks.

3
src/dat/mcx.h
View File

@@ -14,9 +14,8 @@ struct mcx_chunk {
u32 time; // modification time in epoch seconds
};
// TODO: should return some form of feedback about its success
/* Deletes chunk `idx` from `buf`, moving all chunks downwards in the process. */
void mcx_delchunk(u8 *restrict buf, int idx);
size_t 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;