On Monday, 1 June 2015 at 21:44:57 UTC, Steven Schveighoffer
wrote:
On 6/1/15 5:29 PM, Oleg B wrote:
Hello. I found unexpected (for me) behavior of rounding double
values at
casting to ulong:
$ cat roundtest.d
import std.stdio;
void main()
{
double a = 10, b = 0.01;
writeln( "int: ", cast(int)(a/b) );
writeln( "uint: ", cast(uint)(a/b) );
writeln( "long: ", cast(long)(a/b) );
writeln( "ulong: ", cast(ulong)(a/b) );
}
$ rdmd roundtest.d
int: 1000
uint: 1000
long: 1000
ulong: 999 <----- WTF?? -------
These are NOT roundings. They are truncations.
Note that for floating point 0.01 is not representable exactly.
This is the reason you get the error. On other systems, you may
not get errors for this one case, but you could get errors for
other. Please read about floating point error:
http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems
-Steve
Nonetheless, surely in this case the values should be the same
regardless of the integer target type, no?
