Re: [PATCH 31/32] commit-graph.c: fix code that could convert the result of an integer multiplication to a larger type

[Junio C Hamano <gitster@pobox.com>]

Elia Pinto <gitter.spiros@gmail.com> writes:

> Fix the LGTM warning fired by the rule that finds code that could convert the result of an integer
> multiplication to a larger type. Since the conversion applies after the multiplication,
> arithmetic overflow may still occur.

Overly long?

>  	chunk_offsets[0] = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
>  	chunk_offsets[1] = chunk_offsets[0] + GRAPH_FANOUT_SIZE;
> -	chunk_offsets[2] = chunk_offsets[1] + hashsz * ctx->commits.nr;
> -	chunk_offsets[3] = chunk_offsets[2] + (hashsz + 16) * ctx->commits.nr;
> +	chunk_offsets[2] = chunk_offsets[1] + (uint64_t)hashsz * ctx->commits.nr;
> +	chunk_offsets[3] = chunk_offsets[2] + ((uint64_t)hashsz + 16) * ctx->commits.nr;

chunk_offsets[] is u64[], while hashsz and is uint and
ctx->commits.nr is int.  OK.

> @@ -1426,7 +1426,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
>  	}
>  	if (ctx->num_commit_graphs_after > 1) {
>  		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
> -						hashsz * (ctx->num_commit_graphs_after - 1);
> +						(uint64_t)hashsz * (ctx->num_commit_graphs_after - 1);

Likewise.

> @@ -1454,7 +1454,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
>  			    num_chunks);
>  		ctx->progress = start_delayed_progress(
>  			progress_title.buf,
> -			num_chunks * ctx->commits.nr);
> +			(uint64_t)num_chunks * ctx->commits.nr);

Hmph, do we need this?  I understand that the second parameter to
the callee is u64, so the caller needs to come up with u64 without
overflow, but doesn't that automatically get promoted?

>  	}
>  	write_graph_chunk_fanout(f, ctx);
>  	write_graph_chunk_oids(f, hashsz, ctx);