Subject: Re: [PATCH 2/6] commit: add generation number to struct commmit

From: Brandon Williams <[email-masked]>
Date: Tue, 3 Apr 2018 11:05:36 -0700

On 04/03, Derrick Stolee wrote:
> 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

Is there any reason to believe this would be too small of a value in the
future?  Or is a 32 bit unsigned good enough?

> information to revision walks. We use two special values to signal
> the generation number is invalid:
> 
> GENERATION_NUMBER_UNDEF 0xFFFFFFFF
> GENERATION_NUMBER_NONE 0
> 
> The first (_UNDEF) means the generation number has not been loaded or
> computed. The second (_NONE) means the generation number was loaded
> from a commit graph file that was stored before generation numbers
> were computed.
> 
> Signed-off-by: Derrick Stolee <[email-masked]>
> ---
>  alloc.c        | 1 +
>  commit-graph.c | 2 ++
>  commit.h       | 3 +++
>  3 files changed, 6 insertions(+)
> 
> diff --git a/alloc.c b/alloc.c
> index cf4f8b61e1..1a62e85ac3 100644
> --- a/alloc.c
> +++ b/alloc.c
> @@ -94,6 +94,7 @@ void *alloc_commit_node(void)
>  	c->object.type = OBJ_COMMIT;
>  	c->index = alloc_commit_index();
>  	c->graph_pos = COMMIT_NOT_FROM_GRAPH;
> +	c->generation = GENERATION_NUMBER_UNDEF;
>  	return c;
>  }
>  
> diff --git a/commit-graph.c b/commit-graph.c
> index 1fc63d541b..d24b947525 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -264,6 +264,8 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
>  	date_low = get_be32(commit_data + g->hash_len + 12);
>  	item->date = (timestamp_t)((date_high << 32) | date_low);
>  
> +	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
> +
>  	pptr = &item->parents;
>  
>  	edge_value = get_be32(commit_data + g->hash_len);
> diff --git a/commit.h b/commit.h
> index e57ae4b583..3cadd386f3 100644
> --- a/commit.h
> +++ b/commit.h
> @@ -10,6 +10,8 @@
>  #include "pretty.h"
>  
>  #define COMMIT_NOT_FROM_GRAPH 0xFFFFFFFF
> +#define GENERATION_NUMBER_UNDEF 0xFFFFFFFF
> +#define GENERATION_NUMBER_NONE 0
>  
>  struct commit_list {
>  	struct commit *item;
> @@ -24,6 +26,7 @@ struct commit {
>  	struct commit_list *parents;
>  	struct tree *tree;
>  	uint32_t graph_pos;
> +	uint32_t generation;
>  };
>  
>  extern int save_commit_buffer;
> -- 
> 2.17.0.rc0
> 

-- 
Brandon Williams