On Wednesday, 27 December 2017 at 13:40:28 UTC, rumbu wrote:
Is that normal?
use std.math;
float f = float.max;
f += 1.0;
assert(IeeeFlags.overflow) //failure
assert(f == float.inf) //failure, f is in fact float.max
On the contrary, float.max + float.max will overflow. The
behavior is the same for double and real.
This is actually correct floating point behavior. Consider the
following program:
float nextReprensentableToMax = float.max;
// find next smaller representable floating point number
(*cast(int*)&nextReprensentableToMax)--;
writefln("%f", float.max - nextReprensentableToMax);
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.
When trying to understand how floating point works I would highly
recommend that you read these articles (oldest first):
https://randomascii.wordpress.com/category/floating-point/
Kind Regards
Benjamin Thaut
