Github/littlefs
1
Fork 0
Code Actions Activity

Re-upped on-disk leb128 limit for tags to 5-bytes

Browse Source 
This gives us the full 16-bit range of ids (65536) instead of the much
smaller 12-bit range (4096) when limited to truncated 4-byte leb128s.

The real motivation for the truncated 4-byte leb128s is to keep the
wasted space in crc padding down, which this doesn't matter for.

In the future this may be configurable. Or maybe not. Only if truncated
leb128 tags prove to have value, at the moment it looks more like a
premature optimization if anything...

Either way we do need to test for overflowing this.
This commit is contained in:
Christopher Haster
2023-01-18 15:37:08 -06:00
parent d08497c299
commit 27e4fbd3ad
1 changed files with 4 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lfs.c
+4 -4
View File
@@ -1057,7 +1057,7 @@ static lfs_ssize_t lfsr_rbyd_readtag(lfs_t *lfs,
// read a pair of leb128s
//
// note we force leb decoding to overflow when truncated
uint8_t buffer[2*4] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
uint8_t buffer[5+4] = {0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff};
lfs_size_t i = 0;
// TODO allow different hint for lookup? bench this? does our hint work backwards?
@@ -1083,7 +1083,7 @@ static lfs_ssize_t lfsr_rbyd_readtag(lfs_t *lfs,
}
lfsr_tag_t tag_;
ssize_t delta = lfs_fromleb128(&tag_, &buffer[i], 4);
ssize_t delta = lfs_fromleb128(&tag_, &buffer[i], 5);
if (delta < 0) {
return delta;
}
@@ -1455,10 +1455,10 @@ static int lfsr_rbyd_progtag(lfs_t *lfs, lfsr_rbyd_t *rbyd_,
tag |= lfs_popc(rbyd_->crc) & 1;
// compress into pair of leb128s
uint8_t buffer[2*4];
uint8_t buffer[5+4];
lfs_size_t delta = 0;
ssize_t delta_ = lfs_toleb128(tag, &buffer[delta], 4);
ssize_t delta_ = lfs_toleb128(tag, &buffer[delta], 5);
if (delta_ < 0) {
return delta_;
}