Don wrote:
Andrei Alexandrescu wrote:
auto rng = Random(unpredictableSeed);
auto a = 0.0, b = 1.0;
auto x1 = uniform!("[]")(rng, a, b);
auto x2 = uniform!("[)")(rng, a, b);
auto x3 = uniform!("(]")(rng, a, b);
auto x4 = uniform!("()")(rng, a, b);
This is a general issue applying to any numeric range. I've been giving
the issue of numeric ranges some thought, and I have begun an
implementation of a general abstraction.
Any open range can be converted into a closed range, but the converse
does not apply. So any implementation will be using "[]" internally.
-range("[)", a, b) == range("(]", -b, -a)
range("[)", a, b) == range("[]", a, predecessor(b))
range("()", a, b) == range("[]", successor(a), predecessor(b))
There's a couple of difficult situations involving floating-point numbers.
* "[)" has the uncomfortable property that (-2,-1, rng) includes -2 but
not -1, whereas (1, 2, rng) includes 1 but not 2.
* any floating point range which includes 0 is difficult, because there
are so many numbers which are almost zero. The probability of getting a
zero for an 80-bit real is so small that you probably wouldn't encounter
it in your lifetime. I think this weakens arguments based on analogy
with the integer case.
However, it is much easier to make an unbiased rng for [1,2) than for
[1,2] or (1,2) (since the number of members in the range is even).
So what would you recommend? [a, b) for floats and [a, b] for ints, or
[a, b) for everything?
Andrei
