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Dropped "has id" bit encoding in favor of invalid id

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I've been trying to keep tag types organized with an encoding that hints
if a tag uses its id field for file ids. However this seem to have been
a mistake. Using a null id of 0x3ff greatly simplified quite a bit of
the logic around managing file related tags.

The downside is one less id we can use, but if we look at the encoding
cost, donating one full bit costs us 2^9 id permutations vs 1 id
permutation. So even if we had a perfect encoding it's in our favor to
use a null id. The cost of null ids is code size, but with the
complexity around figuring out if a type used it's id or not it just
works out better to use a null id.
This commit is contained in:
Christopher Haster
2018-07-09 14:51:57 -05:00
parent b7bd34f461
commit fd121dc2e2
3 changed files with 16 additions and 23 deletions
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12
tests/test_move.sh
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@@ -59,7 +59,7 @@ tests/test.py << TEST
lfs_rename(&lfs, "b/hello", "c/hello") => 0;
lfs_unmount(&lfs) => 0;
TEST
truncate -s-11 blocks/6
truncate -s-7 blocks/6
tests/test.py << TEST
lfs_mount(&lfs, &cfg) => 0;
lfs_dir_open(&lfs, &dir[0], "b") => 0;
@@ -86,8 +86,8 @@ tests/test.py << TEST
lfs_rename(&lfs, "c/hello", "d/hello") => 0;
lfs_unmount(&lfs) => 0;
TEST
truncate -s-11 blocks/8
truncate -s-11 blocks/a
truncate -s-7 blocks/8
truncate -s-7 blocks/a
tests/test.py << TEST
lfs_mount(&lfs, &cfg) => 0;
lfs_dir_open(&lfs, &dir[0], "c") => 0;
@@ -166,7 +166,7 @@ tests/test.py << TEST
lfs_rename(&lfs, "b/hi", "c/hi") => 0;
lfs_unmount(&lfs) => 0;
TEST
truncate -s-11 blocks/7
truncate -s-7 blocks/7
tests/test.py << TEST
lfs_mount(&lfs, &cfg) => 0;
lfs_dir_open(&lfs, &dir[0], "b") => 0;
@@ -193,8 +193,8 @@ tests/test.py << TEST
lfs_rename(&lfs, "c/hi", "d/hi") => 0;
lfs_unmount(&lfs) => 0;
TEST
truncate -s-11 blocks/9
truncate -s-11 blocks/b
truncate -s-7 blocks/9
truncate -s-7 blocks/b
tests/test.py << TEST
lfs_mount(&lfs, &cfg) => 0;
lfs_dir_open(&lfs, &dir[0], "c") => 0;