Re: rigorously predictable random numbers

[Roman Perepelitsa <roman.perepelitsa@xxxxxxxxx>]

On Mon, May 20, 2024 at 7:41 PM Kannan Varadhan <kvaradhan3@xxxxxxxxx> wrote:
>
> Hi folks:
>
> This was an interesting pointer.  I am puzzled about some of the
> zsh-isms here and the logic, so
>
> some questions:
>
> >      while (( $#bytes < 4 )); do
> >        sysread -s$((4-$#bytes)) 'bytes[$#bytes+1]' </dev/urandom || return
> >      done
>
> It looks like we want 4 individual byes (the sysread promises anywhere
> from 1 to size of buffer specified, max 8192 (in zshmodules(1)) but may
> return after only reading 1B.    So why not only say `-s1` instead of
> the more involved `-s$((4-$#bytes))`?

Reading 1 byte at a time is slower than reading 4 bytes at once.

> >      local b1=$bytes[1] b2=$bytes[2] b3=$bytes[3] b4=$bytes[4]
> >      return '#b1 << 24 | #b2 << 16 | #b3 << 8 | #b4'
>
> Why copy to a scalar parameters

My goal was to implement the contract described in the comments. This
is how I managed to do it. Your asking "why" appears to imply that you
have another implementation in mind that is more natural to you. If
so, can you post it?

> what does referring to them as '#b1', #b2', ... mean.

These are the numeric values of the bytes held in b1..b4.

    % x='A'
    % print -r -- $(( #x ))
    65

Roman.