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Fixed some minor issues with did generation

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- We need to clamp dids to 31-bits. We were clamping to 32-bits
  correctly, but we rely on dids fitting in 31-bits to fit them into our
  lfsr_data_t type.

  This does make our dids more dense when the mtree is near full, but
  keeping dids 31-bits (or bound to the file size type) also gives us
  more flexibility when it comes to deduplicating common leb128 operations.

- We weren't using the right mask during collision resolution. This was
  just an oversight and an unimpactful fix.

  Also saved 4 bytes, which is probably the cost of storing the outdated
  constant in a nearby constant pool. We don't really care.
This commit is contained in:
Christopher Haster
2023-07-31 01:07:15 -05:00
parent 741a9ae652
commit 08ab470c2b
1 changed files with 8 additions and 7 deletions
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lfs.c
+6 -5
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@@ -7297,12 +7297,13 @@ int lfsr_mkdir(lfs_t *lfs, const char *path) {
// 4096/32 = 128, so a filesystem with a single mdir encodes dids in a // 4096/32 = 128, so a filesystem with a single mdir encodes dids in a
// single byte. // single byte.
// //
lfs_size_t did = lfs_crc32c(0, path, strlen(path)) // Note we also need to be careful to catch integer overflow.
// note we need to be careful to catch integer overflow //
& ((1 << lfs_min32( lfs_size_t dmask = (1 << lfs_min32(
lfs_nlog2(lfsr_mtree_weight(lfs)) lfs_nlog2(lfsr_mtree_weight(lfs))
+ lfs_nlog2(lfs->cfg->block_size/32), + lfs_nlog2(lfs->cfg->block_size/32),
32)) - 1); 32)) - 1;
lfs_size_t did = lfs_crc32c(0, path, strlen(path)) & dmask;
// Check if we have a collision. If we do, search for the next // Check if we have a collision. If we do, search for the next
// available did // available did
@@ -7319,7 +7320,7 @@ int lfsr_mkdir(lfs_t *lfs, const char *path) {
} }
// try the next did // try the next did
did = (did + 1) & 0xfffffff; did = (did + 1) & dmask;
} }
// found a good did, now to commit to the mtree // found a good did, now to commit to the mtree