Re: [PATCH v4 3/6] commit-graph: turn on commit-graph by default

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Sep 20, 2021, 01:25 UTC
Message-ID: <YUfjIjgk2IwcJNI8@camp.crustytoothpaste.net>
In-Reply-To: <xmqq8rzsdqlq.fsf@gitster.g>

On 2021-09-20 at 00:42:57, Junio C Hamano wrote:

Show 32 quoted lines

> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
> > diff --git a/repo-settings.c b/repo-settings.c
> > index 309577f6bc..d00b675687 100644
> > --- a/repo-settings.c
> > +++ b/repo-settings.c
> > @@ -2,6 +2,8 @@
> >  #include "config.h"
> >  #include "repository.h"
> >  
> > +#define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
> > +
> >  void prepare_repo_settings(struct repository *r)
> >  {
> >  	int value;
> > @@ -16,6 +18,8 @@ void prepare_repo_settings(struct repository *r)
> >  		r->settings.core_commit_graph = value;
> >  	if (!repo_config_get_bool(r, "gc.writecommitgraph", &value))
> >  		r->settings.gc_write_commit_graph = value;
> > +	UPDATE_DEFAULT_BOOL(r->settings.core_commit_graph, 1);
> > +	UPDATE_DEFAULT_BOOL(r->settings.gc_write_commit_graph, 1);
> 
> 
> This is a "review comment" that is more than 2 years late X-<, but I
> noticed that this is used to muck with a structure that was
> initialized by filling it with \0377 bytes.
> 
> +           /* Defaults */
> +           memset(&r->settings, -1, sizeof(r->settings));
> 
> but the structure is is full of "int" and "enum", so apparently this
> works only on 2's complement architecture.

This statement is true, but are there systems capable of running Git which don't use two's complement? Rust requires two's complement signed integers, and there's a proposal[0] to the C++ working group to only support two's complement because "[t]o the author’s knowledge no modern machine uses both C++ and a signed integer representation other than two’s complement". That proposal goes on to note that none of MSVC, GCC, or LLVM support other options.

Personally I am not aware of any modern processor which provides signed integer types using other than two's complement.

[0] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0907r4.html

-- 
brian m. carlson (he/him or they/them)
Toronto, Ontario, CA