Re: Generating pseudo-random integers

[Pádraig Brady]

On 05/02/11 07:51, Jim Meyering wrote:
> Melikamp T. Medley wrote:
> 
>> Thanks!
>>
>> I think I want to write a utility that prints pseudo-random
>> integers (I have in CL, but I like it fast, so this time in C),
>> and link it with coreutils. I looked at Paul Eggert's work,
>> and I won't be able to do any better than that if I spend
>> years on it :) I want to print uniformly distributed integers
>> fast, formatted, in bulk if needed. And I want to call it roll.
>> Let me know if you have a word of advice.
>>
>> On 02/04/2011 11:35 PM, Eric Blake wrote:
>>> Using just coreutils, though, I'm afraid your options are slim.  You
>>> could use 'seq 0 9 | sort -R | head -n1' (or use shuf instead of sort
>>> -R) to generate one random number at a time, but that gets expensive.
>>> Or, if you don't mind limiting yourself to 62**6 values (instead of the
>>> more traditional 2**32), you could do 'mkdir tmp; mktemp -u -p tmp
>>> XXXXXX'.  But that's the extent of coreutils' randomness exposed to the
>>> user.
> 
> It's hard to justify writing a new program in C
> when you can do the job with a Perl one-liner:
> 
>   $ perl -le 'foreach (1..20) { print int rand 1000 }'
>   423
>   619
>   917
>   396
>   957
>   345
>   892
>   13
>   424
>   519
>   898
>   689
>   208
>   383
>   605
>   196
>   384
>   893
>   618
>   344
> 
> However, adding an *option* to shuf might make sense,
> since you can already give shuf both a range and a count
> of how many numbers to print.

Sorry for being dense, but what option shuf is needed? formatting?

Though on trying shuf to generate the numbers I notice:

$ shuf -i0-$((2**31)) -n1
1241475845
$ shuf -i0-$((2**31)) -n2
shuf: memory exhausted

cheers,
Pádraig.