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

reply d-bugmail puremagic.com writes:
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 puremagic.com
        ReportedBy: bearophile_hugs eml.cc



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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Nov 19 2010
next sibling parent d-bugmail puremagic.com writes:
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A specialized overload/function like this is useful in Phobos even if it's not
faster.

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Nov 19 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Denis Derman <denis.spir gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |denis.spir gmail.com



---
I would vote for uniform01(). Having it called random() would implicitely
promote to the default random function, from which all other forms of random
would/should be computed.

Denis

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Nov 21 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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strtr despam.it changed:

           What    |Removed                     |Added
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                 CC|                            |strtr despam.it



I am probably missing something, but what is wrong with uniform!(0,1) ?
Then you can add optimizations for all the special cases you want.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 I am probably missing something, but what is wrong with uniform!(0,1) ?
 Then you can add optimizations for all the special cases you want.


Currently uniform() uses run-time arguments, not template ones.

--------------------------------------

See also:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=122634

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Nov 22 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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I was commenting on the suggested name uniform01.
Templating the function seemed obvious to me and I was also surprised you
didn't suggest doing that so I thought I was missing something there.

As for speed, as tn mentioned on the newsgroup, subnormal numbers considerately
slow down calculations.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 I was commenting on the suggested name uniform01.
 Templating the function seemed obvious to me and I was also surprised you
 didn't suggest doing that so I thought I was missing something there.


I don't like the idea of a templated ranged uniform. In most cases is not what
I need or what's better.



 As for speed, as tn mentioned on the newsgroup, subnormal numbers considerately
 slow down calculations.


It's in the link of Comment 4

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Nov 22 2010
prev sibling parent d-bugmail puremagic.com writes:
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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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Jan 09 2011