> From: Jeff King <peff@xxxxxxxx>
>
> In a following patch we will allocate a variable number
> of words in some bitmaps. When iterating over the words we
> will need a mark to tell us when to stop iterating. Let's
> always allocate 2 more words, that will always contain 0,
> as that mark.
[snip]
> if (block >= self->word_alloc) {
> size_t old_size = self->word_alloc;
> - self->word_alloc = block * 2;
> + self->word_alloc = (block + 1) * 2;
> REALLOC_ARRAY(self->words, self->word_alloc);
> memset(self->words + old_size, 0x0,
> (self->word_alloc - old_size) * sizeof(eword_t));
This patch set was mentioned as needing more thorough review in "What's
Cooking" [1], so I thought I'd give it a try. As Peff said [2], the
justification in the commit message looks incorrect. He suggests that it
is most likely because "block" might be 0 (which is possible because a
previous patch eliminated the minimum of 32), which makes sense to me.
In any case, the next patch does not use 0 as a sentinel mark. Iteration
stops when word_alloc is reached anyway, and since this is a regular
bitmap, 0 is a valid word and cannot be used as a sentinel. (Maybe 0 is
a valid word in a compressed EWAH bitmap too...not sure about that.)
I think this should be squashed with patch 3, adding to that commit
message "since word_alloc might be 0, we need to change the growth
function". (Or just make the minimum word_alloc be 1 or 32 or something
positive, if that's possible.)
[1] https://public-inbox.org/git/xmqq36g5444k.fsf@xxxxxxxxxxxxxxxxxxxxxxxxx/
[2] https://public-inbox.org/git/20191002155721.GD6116@xxxxxxxxxxxxxxxxxxxxx/
