Re: Issues with rand()

[Daniel J S. <dan...@ie...>]

Ethan Merritt wrote:
> On Tuesday, December 28, 2010, Daniel J Sebald wrote:
> 
>> Ethan Merritt wrote:
[snip]
>> A couple odd things however.  Why is the limiting value
>> 017777777777UL? Is that some bad way of obtaining the maximum 32
>> value of 2^32-1, i.e., 4294967295?
> 
> I think the intent is to make sure that the integer value didn't
> overflow before being converted to (double). Off the top of my head,
> I can't explain why the test isn't against 037777777777 instead.
> 
> 
> 
>> If not, then it should be
>> 
>> if (real(init) >= (double)(04294967295UL)) 
>> int_error(NO_CARET,"Illegal seed value"); if (imag(init) >=
>> (double)(04294967295UL)) int_error(NO_CARET,"Illegal seed value");
> 
> 
> Why?  All bits set is easy to remember; the numerical value
> 4294967295 - not so easy.

Oh yeah, octal.  I'm used to thinking either decimal or hex.  Right, 10 sevens is 30 bits equal 1, so 2 more bits would be a value of 3. 037777777777UL makes more sense.

[snip]
>> Regarding the out of date comment, did it mean that seed1 and seed2
>> should be 64-bit, i.e., long long?
> 
> 
> Upon reflection, I think the comment is pointing out that since we
> just disallowed any values with the high bit set you can only set the
> low 31 bits of each half.  I.e. only 62 of the 64 bits can be set.

Shouldn't be a problem if using 037777777777UL.

As you pointed out, placing one seed in the real component and one seed in the imaginary component is a bit peculiar.  Can the rand() function simply have two optional inputs?

Dan