https://issues.dlang.org/show_bug.cgi?id=15763
Issue ID: 15763
Summary: std.math.approxEqual is not symmetric
Product: D
Version: D2
Hardware: All
OS: All
Status: NEW
Severity: minor
Priority: P1
Component: phobos
Assignee: [email protected]
Reporter: [email protected]
Current implementation of std.math.approxEqual is not symmetric. The code
below gives an example.
import std.math : eq = approxEqual;
immutable real
a = (2e-3)-(1e-5),
b = (2e-3)+(1e-5);
assert ( a.eq(b)); // (error relative to b) = 1 / (100.5)
assert (!b.eq(a)); // (error relative to a) = 1 / ( 99.5)
IMO at least we need to document this. It may be enough since the case this
asymmetricity do something harm is rare.
If we "fix" it, we must consider the backward compatibility, and/or
performance.
I would be pleased with an alternative for approxEqual like this:
return ((a - b).abs < abserr) || ((a - b).abs / (a.abs + b.abs) < relerr / 2);
Any opinion?
--
