On Wednesday, 27 December 2017 at 14:14:42 UTC, Benjamin Thaut
wrote:
On Wednesday, 27 December 2017 at 13:40:28 UTC, rumbu wrote:
Is that normal?
It computes the difference between float.max and the next
smaller reprensentable number in floating point. The difference
printed by the program is:
20282409603651670423947251286016.0
As you might notice this is siginificantly bigger then 1.0.
Floating point operations work like this: They perform the
operation and then round to the nearest representable number in
floating point. So adding 1.0 to float.max and then rounding to
the nearest representable number will just give you back
float.max. If you however add float.max and float.max the next
nearest reprensentable number is float.inf.
The float with the lower exponent would have to be shifted to
match the higher which means 1.0 would be shifted something like
156 bits to the right before the addition can be done. If you
shift right more bits than are in the mantissa then it get
rounded to zero. Hence once the two values are lined up to do the
actual op it becomes float.max + 0.0.
That said i suspect the OP was expecting the FPU unit to catch
that in theory it should overflow. Not that the actual op would
overflow but that the FPU would be checking the values on input.
Maybe.
