Re: random numbers

Sure.  More generally, you can get a pseudo-random integer from 0 to N-1 by
rerolling whenever you get anything > N*floor(32767/N). My point was that
even if you don't do that, the actual variation from uniformity is not huge
as long as you keep your divisor in a reasonable range relative to 32767.

On Mon, Sep 15, 2025 at 3:12 PM Roman Perepelitsa <
[email protected]> wrote:

> You can get a uniform random number from [0, 10) like this:
>
>     integer n
>     while true; do
>       (( n = RANDOM ))
>       if (( n <= 32760 )); then
>         (( n %= 10 ))
>         break
>       fi
>     done
>
> Roman
>
> On Mon, Sep 15, 2025 at 8:56 PM Mark J. Reed <[email protected]> wrote:
>
>> > I think i know why, it's because zsh's RANDOM tops out at 32,767, but
>> this insures that the first digit of a string of random numbers isn't
>> random but strongly weighted to 1 and 2, with 3 also weighted.
>>
>> I mean, only if you use the whole value of RANDOM directly, which most
>> applications of random numbers don't do. If you do the usual trick of
>> taking the remainder of RANDOM modulo a range, e.g. picking random digits
>> one at a time with (( RANDOM % 10 )), you won't see such a strong
>> weighting. In the case of single digits you are 0.03% less likely to get an
>> 8 or 9 than a 0 through 7, but that's a pretty mild deviation from
>> uniformity.
>>
>> On Mon, Sep 15, 2025 at 9:36 AM Clinton Bunch <[email protected]>
>> wrote:
>>
>>>
>>> I think i know why, it's because zsh's RANDOM tops out at 32,767, but
>>> this insures that the first digit of a string of random numbers isn't
>>> random but strongly weighted to 1 and 2, with 3 also weighted.  Is this
>>> worth worrying about?  I'd say so.  Perhaps it should max out at 10,000 or
>>> 100,000 or even offer a user selectable range?  Or do we have other tricks
>>> for coping with this?  I find zsh to be quite competent mathematically so
>>> having to use an external utility to get really random numbers seems not up
>>> to snuff.
>>>
>>> Check out the zsh/random module in the current test release and the
>>> zrand_int math function.
>>>
>>
>>
>> --
>> Mark J. Reed <[email protected]>
>>
>

-- 
Mark J. Reed <[email protected]>