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Re: useful macros

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"BartC" <bc@freeuk.com> writes:
[...]
> I use a function random(a..b) which returns a random integer from a to b
> inclusive (in a scripting language, but it calls C's rand()).
>
> I've just tested this, and over a large number of calls, it seems to produce
> a uniform distribution down to 0.001% and better. (And it doesn't know what
> RAND_MAX is except that it might be as low as 32767.)
[...]

Does it perform multiple calls to rand() in some cases?

If not, it's not possible to get a completely uniform distribution, a
problem that might be difficult to see on a system with, say, RAND_MAX
== 2147483647.

For example, if RAND_MAX==32767, then there are exactly 32768 equally
likely results from rand(). random(0..30000), if it depends on a single
call to rand(), will return some results twice as often as others;
random(0..40000) cannot return all possible results.

Question 13.16 of the comp.lang.c FAQ covers this.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
    Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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useful macros Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-05-26 13:08 -0700
  Re: useful macros winndy <jiaoyk@gmail.com> - 2012-05-29 20:26 -0700
    Re: useful macros Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-05-30 00:47 -0700
      Re: useful macros Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-05-30 16:45 +0100
        Re: useful macros James Kuyper <jameskuyper@verizon.net> - 2012-05-30 13:10 -0400
          Re: useful macros Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-05-30 21:54 +0100
          Re: useful macros "BartC" <bc@freeuk.com> - 2012-05-30 23:24 +0100
            Re: useful macros James Kuyper <jameskuyper@verizon.net> - 2012-05-30 18:55 -0400
              Re: useful macros "BartC" <bc@freeuk.com> - 2012-05-31 00:45 +0100
            Re: useful macros Keith Thompson <kst-u@mib.org> - 2012-05-30 17:53 -0700
              Re: useful macros "BartC" <bc@freeuk.com> - 2012-05-31 10:29 +0100

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