The functions's header comment mentions "The bitmapsets are all pre-initialized with an unused high bit so that memory allocation is done only once.".
Ah, I neglected to notice this when reviewing the v1 patch. I guess it's implemented this way due to performance considerations, right?
I've attached a patch which adds bms_replace_members(). It's basically like bms_copy() but attempts to reuse the member from another set. I considered if the new function should be called bms_copy_inplace(), but left it as bms_replace_members() for now.
Do you think we can use 'memcpy(a, b, BITMAPSET_SIZE(b->nwords))' directly in the new bms_replace_members() instead of copying the bitmapwords one by one, like:
- i = 0; - do - { - a->words[i] = b->words[i]; - } while (++i < b->nwords); - - a->nwords = b->nwords; + memcpy(a, b, BITMAPSET_SIZE(b->nwords));
But I'm not sure if this is an improvement or not.