hash: bug: initial hash mask miscalculation.

Hash tables are supposed to start with a mask of 255,
which is the 256 modulus less one. However, due to a
coding mistake, they get a modulus of 252. Now this still
works. It just has a few zero bits in it: 1111 1100
rather than 11111111. When this grows by doubling in size,
we get 1 1111 1001, 11 1111 0011 and so on.
Now this still all works, because hash values AND-ed
with such a mask are no greater than that mask. The
table isn't accessed out of bounds. It's just inefficiently
used.

* hash.c (do_make_hash, make_similar_hash, clearhash):
When converting the power-of-two modulus, which is a Lisp
word, to the integer mask, subtract 1 from the integer
value, not the original Lisp word.

0 files changed, 0 insertions, 0 deletions