Re: [PATCH] zsh/random module [UPDATED]

[Matthew Martin <phy1729@gmail.com>]

On Sun, Nov 20, 2022 at 07:59:54PM -0600, Clinton Bunch wrote:
> On 11/20/2022 7:07 PM, Matthew Martin wrote:
> > I'm not clear on where the getrandom builtin came from. I understand the
> > desire for SRANDOM to have a proper random source in the shell; however,
> > the rest seems like feature creep that if necessary could be implemented
> > with a loop. It seems prudent to keep the initial module to a minimum to
> > ensure there's a usecase and so backwards compat concerns don't crop up.
> > 
> > Would it suffice for your uses to have a module with just SRANDOM?
> 
> One of my use cases is in precmd to replace this function
> 
> get_random() {
>   local retvar=$1;shift
>   local max=${1:-32767}
> 
>   local out=$(( int( rand48(my_seed) * $max + 0.5 ) ))
> 
>   eval "${retvar}=$out"
> }
> 
> used here:
> 
> precmd () {
>   get_random cdb_fg "6"
>   psvar[1]=$(( cdb_fg + 1))
> }
> 
> A better more uniform distribution of random numbers can be achieved with
> 
> getrandom -U 6 -s cdb_fg
> 
> than $SRANDOM % 7 which will have a modulo bias

It's true SRANDOM % 7 would have modulo bias; however, even if only
SRANDOM is provided, the out of range rejection loop could happen in
shell code. While that's less convenient, I am of the opinion once
a user needs to care about modulo bias, they're likely better served by
a language other than shell.

If a uniform random function is desired in zsh, I think it should mirror
the interface of arc4random_uniform: just take an upper_bound and return
a value in the range [0, upper_bound).