commit_list: store in/out-degrees as uint16_t

The commit list's in- and out-degrees are currently stored as `unsigned
short`. When assigning it the value of `git_array_size`, which returns
an `size_t`, this generates a warning on some Win32 platforms due to
loosing precision.

We could just cast the returned value of `git_array_size`, which would
work fine for 99.99% of all cases as commits typically have less than
2^16 parents. For crafted commits though we might end up with a wrong
value, and thus we should definitely check whether the array size
actually fits into the field.

To ease the check, let's convert the fields to store the degrees as
`uint16_t`. We shouldn't rely on such unspecific types anyway, as it may
lead to different behaviour across platforms. Furthermore, this commit
introduces a new `git__is_uint16` function to check whether it actually
fits -- if not, we return an error.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/integer.h b/src/integer.h
index 10b109737..4738e9e35 100644
--- a/src/integer.h
+++ b/src/integer.h
@@ -21,6 +21,13 @@ GIT_INLINE(int) git__is_ssizet(size_t p)
 	return p == (size_t)r;
 }
 
+/** @return true if p fits into the range of a uint16_t */
+GIT_INLINE(int) git__is_uint16(size_t p)
+{
+	uint16_t r = (uint16_t)p;
+	return p == (size_t)r;
+}
+
 /** @return true if p fits into the range of a uint32_t */
 GIT_INLINE(int) git__is_uint32(size_t p)
 {