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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.programming
Subject: Re: Here is why C++ and C are bad...
Date: Wed, 30 Dec 2015 20:26:41 +0000
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Richard Heathfield <rjh@cpax.org.uk> writes:

> On 30/12/15 17:19, David Brown wrote:
>
> <snip>
>
>> You didn't get as far as Python, I take it.
>
> No. I would in any case have chosen PHP for my 'P' language, but from
> what you say below it seems that Python would have been the more
> interesting choice.
>
>> In Python, the integer
>> types just get as big as you need (until you run out of time or memory).
>>   So to a large extent you can assume your integers really are
>> mathematical integers, and add them as much as you want.  (So "unsigned"
>> integers don't really exist.)
>
> What if I wanted to construct a candidate for a large prime? The usual
> way to do this is to pick a number of bits, set the top and bottom
> bits, and then arbitrarily assign other bits (either setting or
> clearing them, as dictated by some entropy source). Then one applies
> Miller-Rabin a few times, and adds 2 if any of the tests
> fail. Traditionally one uses an array of unsigned char for this, but
> if you don't /have/ unsigned char, or indeed any unsigned type,
> presumably you could still do this with code such as:
>
> candidate = 1 << (bitcount - 1);
> candidate |= 1;
> for i = 1 to bitcount - 2
>   candidate |= getrandomnumber(0,1) << i;
>
> ?

Yes (though I'd probably set the bits in larger chucks).  In actual
Python:

    candidate = 1 << (bitcount - 1);
    candidate |= 1;
    for i in range(1, bitcount - 2):
        candidate |= random.randint(0,1) << i;

> (I realise I'm moving away from signed/unsigned here!)

-- 
Ben.