John Maddock skrev:
Thorsten Ottosen wrote:
I don't fully understand this...AFAIK, this is not allowed for an IEEE complient implementation. How could we ever implement *anything* with respect to floats then?
With difficulty :-(
Here's the thought experiment I came up with to verify that this is a real issue:
* Imagine that the constraint is that the value is > 1, and that we're working with double's. * Imagine that the value being assigned is the result of some complex computation, and that the assignment function is inlined. * The compiler may now take the value being assigned as it exists in a register (from the computation), and perform a the check on that. * If the register containing the result is wider than a double (say Intels 80-bit long double), and the result is very slightly > 1, then the comparison will succeed. * The value is now stored in the object - and rounded down to double precision in the process. * The value may have been rounded down to exactly 1, and the constrait is now broken!
Obviously if the constraint had been >= 1 then we'd be OK in this case (but then values very slightly < 1 may get rounded up, so we could eroniously reject a value).
This might be quite OK. At least this preserves the invariant and therefore seems much better than the alternative. -Thorsten