Re: question about random generator

pete wrote:

Eric Sosman wrote:

Peter Nilsson wrote:


Eric Sosman wrote:


...
   The rand() function generates uniformly distributed
integers in the range 0 <= rand() <= RAND_MAX <= 32767.


ITYM: 0 <= rand() <= RAND_MAX, where RAND_MAX >= 32767 

    Indeed, yes, that is exactly and precisely what I,
of course, meant.  (Blbbbpppfft -- I *hate* when I do that.


Does "pseudo-random" mean the same thing as "uniformly distributed" ? 

    No.  The Standard doesn't actually guarantee any particular
distribution from rand().  On the DeathStation 9000, rand()
returns 42 every time you call it.

    I've always assumed that the Standard doesn't describe the
distribution because doing so would require a lot of fairly
deep mathematics; Knuth devotes thirty-five pages to the topic
"What is a random sequence?"  Developing a useful theory of
the randomness of finite sequences is (it seems) no simple
matter -- certainly not a topic for the Standard to explicate.
So the Standard just says "pseudo-random," and we all understand
that it means "sort of uniform-ish in a sort of hand-waving way,
noodge noodge wink wink."

    Anyhow, that's how I've imagined the committee's intent.
The Rationale sheds no further light on the matter, either.

--
Eric Sosman
esosman@xxxxxxxxxxxxxxxxxxx
.

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