From: "Junio C Hamano" <gits...@pobox.com>
"Philip Oakley" <philipoak...@iee.org> writes:
I'm working on building Git on Visual Studio as part of the Git for
Windows
capability.
The MSVC compiler is reporting:
1>..\sha1-lookup.c(100) : warning C4146: unary minus operator applied to
unsigned type, result still unsigned
1>..\sha1-lookup.c(316) : warning C4146: unary minus operator applied to
unsigned type, result still unsigned
the two lines of code are the same, and the message suggests a bad
return value:
#100: return -lo-1;
#316: return -lo-1;
Should these be protected by an appropriate brackets/calculation
(-1-lo) ? Or does
gcc use an alternate assumption about unary minus conversion for
functions
returning int?
I think -lo-1 (which is carried out as unsigned) is further casted
back to signed int as part of the return from the function whose
type is signed int. This may be portable in practice, but changing
type of lo to signed int may be prudent.
sha1_pos() uses size_t, but returns "int", which is inconsistent
(size_t could be much larger). Either using int for hi/lo/mi, or
using ssize_t and returning ssize_t would make sense.
I'm going to hold off on patching this at the moment, as there are a few
more signed/unsigned mismatches that are reported but I've been ignoring
(mainly comparisons), so I'll try and catch them all at the same time,
especially as I now understand the standards issues.
This thread has a summary of the standards
http://stackoverflow.com/questions/8026694/c-unary-minus-operator-behavior-with-unsigned-operands
(includes C++ >> C) while
https://msdn.microsoft.com/en-us/library/4kh09110(v=vs.90).aspx explains
what is being reported.
i.e. unary minus on unsigned ints produces the 2's complement + 1 value,
except for 0x8000h, where that would be out of range. It's an oddball of
partially defined behaviours.
--
Philip
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