On 8/24/15 1:43 PM, bachmeier wrote:
On Monday, 24 August 2015 at 16:52:54 UTC, Márcio Martins wrote:
I'm posting this here for visibility. This was silently corrupting our
data, and might be doing the same for others as well.
import std.stdio;
void main() {
double x = 1.2;
writeln(cast(ulong)(x * 10.0));
double y = 1.2 * 10.0;
writeln(cast(ulong)y);
}
Output:
11
12
to!ulong instead of the cast does the right thing, and is a viable
work-around.
Issue: https://issues.dlang.org/show_bug.cgi?id=14958)
I would not describe to!ulong as a "work-around". You just discovered
one of the reasons to! exists: it is the right way to do it and
cast(ulong) is the wrong way. As the others have noted, floating point
is tricky business, and you need to use the right tools for the job.
real y = x * 10.0;
writeln(y.to!ulong); // 11
to! does not do anything different than cast. What is happening here is
the implicit cast from real to double. D treats the result of x * 10.0
as type double, but it's done at real precision. In that conversion, the
error is hidden by a rounding automatically done by the processor I think.
-Steve
