From: Eric Hodel <drbrain@...7.net>
Date: 2005-07-06T03:19:48+09:00
Subject: Re: Ruby2c and large numbers


On 04 Jul 2005, at 15:22, Garance A Drosehn wrote:

> Checking out the writeup on Ruby2C at:
>
> http://www.zenspider.com/~ryand/Ruby2C.pdf
>
> there is one thing about the example on page 25 (of the pdf)
> which concerns me a little bit.  The example has:
>
> class MyTest
>   def factorial(n)
>     f = 1
>     n.downto(2) { |x| f *= x }
>     return f
>   end
> end
>
> turn into:
>
> static VALUE factorial(VALUE self,
>                         VALUE _n) {
>     long n = NUM2INT(_n);
>     long f;
>     long x;
>     f = 1;
>     x = n;
>     while (x >= 2) {
>         f = f * x;
>         x = x - 1;
>     };
>     return INT2NUM(f);
> }
>
> One nice thing about ruby is that the programmer does not have
> to worry about supported-ranges for integer values.  Ruby just
> switches from "fixnum" objects into "bignum" objects, without
> any attention from the programmer.  It seems to me that the C
> code that is listed above just assumes the multiplication of
> 'f * x' will not overflow.  Is that the case?

You are correct.

We could add the ability to automatically add the bignum/fixnum auto- 
conversion stuff, but we've not needed the capability yet.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
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