Re: [boost] [Random] uniform_int vs. uniform_real vs. uniform_01

From: Jens Maurer (Jens.Maurer_at_[hidden])
Date: 2004-12-31 10:51:14

Doug Gregor wrote:
> I'm having a few problems dealing with uniform_real and uniform_01.
> 
> The basic issue is that uniform_real does not always produce values 
> between its min and its max. 

uniform_real was meant to be used with variate_generate<> only.
Reviewing the language in the ISO C++ TR draft seems to miss
one requirement: That the Engine used as input for uniform_real()
always returns numbers in the range [0..1[, if floating-point numbers
are requested.  This is one of the features of variate_generate<>:
it wraps the original Engine so that this is always the case.

Note that the current ISO C++ TR draft already requires
that the input Engine produce numbers of the "correct" type
(floating-point or integer).

> Looking at the source to uniform_real, the problem is obvious:
> 
>   result_type operator()(Engine& eng) { return eng() * (_max - _min) + 
> _min; }

Yes.  Fixed.

>   However, uniform_01 is also broken in several ways:

uniform_01, at this time, is just an implementation helper
for variate_generator<> and thus should move to the details
namespace ASAP.  Since it's hideously broken for general
use right now, I'm inclined to perform the move without
any deprecation period.

Jens Maurer