[Issue 5240] New: Faster std.random.uniform() for [0.0, 1.0) range

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5240

           Summary: Faster std.random.uniform() for [0.0, 1.0) range
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2010-11-19 07:16:51 PST ---
std.random.uniform() is a powerful and flexible function, but some tests show
that it's slow. It also calls nextafter() that is not fast.

A very common use case is the generation of random doubles in the [0.0, 0.1[
range (open on the right). So I suggest to speed up this special case. This
special case is present in the Python standard module "random" too, it is just
named random().

A way to support it is just to add a uniform() that takes no arguments (and
hopefully it doesn't need to call nextafter() inside):


import std.random: uniform;
void main() {
    double d = uniform(); // equivalent to uniform(0.0, 1.0) but faster
}

This function that takes no arguments may also have a name like "uniform01()"
or "random()".


Another special case that may be worth supporting is the generation of a random
size_t. This is useful because it avoids using floating point values at all,
and probably minimizes other operations too to generate it, so it may be faster
still than the uniform() with no arguments.

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