Re: [PATCH] vcs-svn: Fix some compiler warnings

Jonathan Nieder wrote:

Ramsay Jones wrote:

quoted

In particular, some versions of gcc complains as follows:

        CC vcs-svn/sliding_window.o
    vcs-svn/sliding_window.c: In function `check_overflow':
    vcs-svn/sliding_window.c:36: warning: comparison is always false \
        due to limited range of data type

Yuck.  Suppressing this warning would presumably also suppress the
optimization that notices the comparison is always false.

I didn't check, but I would assume so.  I would prefer not to loose any
chance at optimizing the code, but in this case, given that we are talking
about a fatal error path, I don't think it is much of a loss.

The -Wtype-limits warning also triggers in some other perfectly
reasonable situations: see <http://gcc.gnu.org/PR51712>.

[...]

quoted

Note that the "some versions of gcc" which complain includes 3.4.4 and
4.1.2, whereas gcc version 4.4.0 compiles the code without complaint.

Thanks for tracking this down.  Interesting.  -Wtype-limits was split
out from the default set of warnings (!) in gcc 4.3 to address
<http://gcc.gnu.org/PR12963>, among other bugs (r124875, 2007-05-20).

Thanks for the above references, and for taking the time to track them
down.

Is there some less ugly way to write the condition "if this value is
not representable in this type"?

I guess I could live with something like the following (please don't
take the names too seriously):

	static inline off_t off_t_or_die(uintmax_t val, const char *msg_if_bad)
	{
		if (val > maximum_signed_value_of_type(off_t))
			die("%s", msg_if_bad);
		return (off_t) val;
	}

	...

		off_t delta_len = off_t_or_die(len, "enormous delta");
		postimage_len = apply_delta(delta_len, input, ...);

What do you think?

An static inline function was actually my first thought (although I had
something more like Junio's suggestion [elsewhere in this thread] in mind),
but I didn't want to place it in git-compat-util.h and could not find a
suitable place in the vcs-svn directory.

Hmm, I will send a v2 patch along these lines ...

ATB,
Ramsay Jones