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

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Danh,

On Thu, 7 Nov 2019, Danh Doan wrote:

> On 2019-11-06 11:23:00 +0900, Junio C Hamano wrote:
> > > @@ -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?
>
> Neither num_chunks nor ctx->commits.nr is promoted because both of
> them are int. The result of `num_chunks * ctx->commits.nr' will be int
> and will be promoted to u64 to pass to caller.

If you up-cast, maybe do the second operand so that nobody has to spend
cycles trying to remember whether the cast or the arithmetic operand
bind stronger? I.e. `num_chunks * (uint64_t)ctx->commits.nr`.

Ciao,
Dscho