Derrick Stolee <dsto...@microsoft.com> writes:
> The generation number of a commit is defined recursively as follows:
>
> * If a commit A has no parents, then the generation number of A is one.
> * If a commit A has parents, then the generation number of A is one
> more than the maximum generation number among the parents of A.
>
> Add a uint32_t generation field to struct commit so we can pass this
> information to revision walks. We use two special values to signal
> the generation number is invalid:
>
> GENERATION_NUMBER_ININITY 0xFFFFFFFF
> GENERATION_NUMBER_ZERO 0
>
> The first (_INFINITY) means the generation number has not been loaded or
> computed. The second (_ZERO) means the generation number was loaded
> from a commit graph file that was stored before generation numbers
> were computed.
Should it also be possible for a caller to tell if a given commit
has too deep a history, i.e. we do not know its generation number
exactly, but we know it is larger than 1<<30?
It seems that we only have a 30-bit field in the file, so wouldn't
we need a special value defined in (e.g. "0") so that we can tell
that the commit has such a large generation number? E.g.
> + item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
if (!item->generation)
item->generation = GENERATION_NUMBER_OVERFLOW;
when we read it from the file?
We obviously need to do something similar when assigning a
generation number to a child commit, perhaps like
#define GENERATION_NUMBER_OVERFLOW (GENERATION_NUMBER_MAX + 1)
commit->generation = 1; /* assume no parent */
for (p = commit->parents; p; p++) {
uint32_t gen = p->item->generation + 1;
if (gen >= GENERATION_NUMBER_OVERFLOW) {
commit->generation = GENERATION_NUMBER_OVERFLOW;
break;
} else if (commit->generation < gen)
commit->generation = gen;
}
or something? And then on the writing side you'd encode too large a
generation as '0'.
