On 28 January 2010 12:55, Tony Bernardin <sarusama@xxxxxxxxx> wrote: > > ok, I understand now how 4294967295 is generated in that first case. > Am I understanding right that in the other case at line 18, it works > out "right" because there is no zero-extension and the coercion to a > signed type will interpret the bits "properly"? > In that one it's int32 * uint64, so the (int32)-1 gets promoted to int64, which uses sign-extension, so you get (int64)-1. That then gets reinterpreted as uint64, giving 0xFFFFFFFFFFFFFFFF, but multiplication in twos-complement is the same as unsigned multiplication, so the result just so happens to work out to the value you want. As others have said, I suggest trying on all the warnings you can (-Wsign-conversion in particular, iirc) and being explicit about all such conversions so you're sure what you'll get. ~ Scott
