Re: [PATCH] vcs-svn: Fix some compiler warnings
From: Jonathan Nieder <hidden>
Date: 2016-06-15 22:52:54
Hi, Ramsay Jones wrote:
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 typeYuck. Suppressing this warning would presumably also suppress the optimization that notices the comparison is always false. The -Wtype-limits warning also triggers in some other perfectly reasonable situations: see <http://gcc.gnu.org/PR51712>. I wonder if we should keep a list of unreliable warnings somewhere (e.g., Meta/Make). [...]
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). [...]
quoted hunk ↗ jump to hunk
--- a/vcs-svn/fast_export.c +++ b/vcs-svn/fast_export.c@@ -300,7 +300,8 @@ void fast_export_blob_delta(uint32_t mode, uint32_t len, struct line_buffer *input) { long postimage_len; - if (len > maximum_signed_value_of_type(off_t)) + uintmax_t delta_len = (uintmax_t) len; + if (delta_len > maximum_signed_value_of_type(off_t)) die("enormous delta"); postimage_len = apply_delta((off_t) len, input, old_data, old_mode);
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?
Jonathan