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add comments to point at where strict aliasing rule violations occur in data scripts

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this is definitely not all of them, a thorough rewrite must take place
to fix as many as we can.
This commit is contained in:
Quinn
2025-09-03 22:39:15 +02:00
parent 55635d44ae
commit b72b8eaee1
2 changed files with 13 additions and 9 deletions
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12
src/dat/mcx.c
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@@ -18,8 +18,8 @@
/* 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
u32 *table = (u32 *)buf; // BUG: strict aliasing
size_t len = src - dst; // acquire the amount of bytes that we shall move
assert(!(len % SECTOR));
// count how many bytes we need to move, whilst updating location data
@@ -36,7 +36,7 @@ static void mvchunks(u8 *restrict buf, u8 *src, u8 *dst, int src_s, int src_e) {
* 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
u32 *table = (u32 *)buf;
u32 *table = (u32 *)buf; // BUG: strict aliasing
size_t slen, bidx, blen;
slen = be32toh(table[sidx]) & 0xFF; // acquire the sector length of the chunk
bidx = (be32toh(table[sidx]) >> 8) * SECTOR; // acquire and compute the byte offset the chunk starts at
@@ -62,7 +62,7 @@ size_t mcx_delchunk(u8 *restrict buf, int chunk) {
size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) {
assert(start < end && end < CHUNKS);
u32 *table = (u32 *)buf;
u32 *table = (u32 *)buf; // BUG: strict aliasing
u8 *dst = buf + (be32toh(table[start]) >> 8) * SECTOR;
u8 *src = buf + (be32toh(table[end]) >> 8) * SECTOR;
src += (be32toh(table[end]) & 0xFF) * SECTOR;
@@ -70,8 +70,8 @@ size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) {
// 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 + CHUNKS] = ts;
table[i] = 0; // BUG: strict aliasing
table[i + CHUNKS] = ts; // BUG: strict aliasing
}
// move the remaining chunks down