> On Apr 26, 2016, at 10:03 AM, Nicola Salmoria via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> it should be enough to do
>
> func <= <T: FloatingPoint>(lhs: T, rhs: T) -> Bool
> {
> return lhs.isLess(than: rhs) || lhs.isEqual(to: rhs)
> }
>
> Or is there some case of x, y where (x <= y) is true but (x < y) and (x == y)
> are both false?
No, these are always equivalent.
However, there is a problem with this approach: the compiler knows about the
built-in floating-point types (Float, Double, Float80) and their aliases
(CGFloat, etc) and can fuse the two comparisons into a single hardware
operation. However, for soft-float types, without a lessThanOrEqual method,
there is no single comparison that the compiler could fuse these to.
In some cases, if they are simple enough, the compiler may be able to actually
fuse the bodies of the two comparison operations, but we can’t reasonably
depend on that happening or even being possible in all cases. So for
performance, it’s important that there be an actual less than or equal to
method.
– Steve
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