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Posted to dev@commons.apache.org by Greg Sterijevski <gs...@gmail.com> on 2011/08/29 07:17:26 UTC
[math] MersenneTwister question
Hello All,
In the MersenneTwister implementation in commons, I notice the following:
@Override
public void setSeed(int seed) {
// we use a long masked by 0xffffffffL as a poor man unsigned int
long longMT = seed;
mt[0]= (int) longMT;
for (mti = 1; mti < N; ++mti) {
// See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier.
// initializer from the 2002-01-09 C version by Makoto Matsumoto
longMT = (1812433253l * (longMT ^ (longMT >> 30)) + mti) &
0xffffffffL;
mt[mti]= (int) longMT;
}
}
While probably not a big deal, shouldn't the initial element in the array mt
be 'anded' by 0xffffffffL?
mt[0]= (int) longMT & 0xffffffffL;
Thanks,
-Greg
Re: [math] MersenneTwister question
Posted by Greg Sterijevski <gs...@gmail.com>.
Yes, I think this is a good idea. I will do it.
On Tue, Aug 30, 2011 at 5:37 AM, sebb <se...@gmail.com> wrote:
> On 29 August 2011 07:11, Greg Sterijevski <gs...@gmail.com> wrote:
> > My apologies, I was looking at the original c code and neglected to
> notice
> > the cast.
>
> Perhaps add a comment to the cast to make it clearer?
>
> > On Mon, Aug 29, 2011 at 12:56 AM, Greg Sterijevski
> > <gs...@gmail.com>wrote:
> >
> >> Yes, you seem to have a good point. My bad.
> >>
> >> On Mon, Aug 29, 2011 at 12:50 AM, Ted Dunning <ted.dunning@gmail.com
> >wrote:
> >>
> >>> Why?
> >>>
> >>> Isn't that what casting as an (int) does?
> >>>
> >>> On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
> >>> <gs...@gmail.com>wrote:
> >>>
> >>> > While probably not a big deal, shouldn't the initial element in the
> >>> array
> >>> > mt
> >>> > be 'anded' by 0xffffffffL?
> >>> >
> >>> > mt[0]= (int) longMT & 0xffffffffL;
> >>> >
> >>>
> >>
> >>
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: dev-unsubscribe@commons.apache.org
> For additional commands, e-mail: dev-help@commons.apache.org
>
>
Re: [math] MersenneTwister question
Posted by Greg Sterijevski <gs...@gmail.com>.
Added short comment. -Greg
On Tue, Aug 30, 2011 at 5:37 AM, sebb <se...@gmail.com> wrote:
> On 29 August 2011 07:11, Greg Sterijevski <gs...@gmail.com> wrote:
> > My apologies, I was looking at the original c code and neglected to
> notice
> > the cast.
>
> Perhaps add a comment to the cast to make it clearer?
>
> > On Mon, Aug 29, 2011 at 12:56 AM, Greg Sterijevski
> > <gs...@gmail.com>wrote:
> >
> >> Yes, you seem to have a good point. My bad.
> >>
> >> On Mon, Aug 29, 2011 at 12:50 AM, Ted Dunning <ted.dunning@gmail.com
> >wrote:
> >>
> >>> Why?
> >>>
> >>> Isn't that what casting as an (int) does?
> >>>
> >>> On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
> >>> <gs...@gmail.com>wrote:
> >>>
> >>> > While probably not a big deal, shouldn't the initial element in the
> >>> array
> >>> > mt
> >>> > be 'anded' by 0xffffffffL?
> >>> >
> >>> > mt[0]= (int) longMT & 0xffffffffL;
> >>> >
> >>>
> >>
> >>
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: dev-unsubscribe@commons.apache.org
> For additional commands, e-mail: dev-help@commons.apache.org
>
>
Re: [math] MersenneTwister question
Posted by sebb <se...@gmail.com>.
On 29 August 2011 07:11, Greg Sterijevski <gs...@gmail.com> wrote:
> My apologies, I was looking at the original c code and neglected to notice
> the cast.
Perhaps add a comment to the cast to make it clearer?
> On Mon, Aug 29, 2011 at 12:56 AM, Greg Sterijevski
> <gs...@gmail.com>wrote:
>
>> Yes, you seem to have a good point. My bad.
>>
>> On Mon, Aug 29, 2011 at 12:50 AM, Ted Dunning <te...@gmail.com>wrote:
>>
>>> Why?
>>>
>>> Isn't that what casting as an (int) does?
>>>
>>> On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
>>> <gs...@gmail.com>wrote:
>>>
>>> > While probably not a big deal, shouldn't the initial element in the
>>> array
>>> > mt
>>> > be 'anded' by 0xffffffffL?
>>> >
>>> > mt[0]= (int) longMT & 0xffffffffL;
>>> >
>>>
>>
>>
>
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Re: [math] MersenneTwister question
Posted by Greg Sterijevski <gs...@gmail.com>.
My apologies, I was looking at the original c code and neglected to notice
the cast.
On Mon, Aug 29, 2011 at 12:56 AM, Greg Sterijevski
<gs...@gmail.com>wrote:
> Yes, you seem to have a good point. My bad.
>
> On Mon, Aug 29, 2011 at 12:50 AM, Ted Dunning <te...@gmail.com>wrote:
>
>> Why?
>>
>> Isn't that what casting as an (int) does?
>>
>> On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
>> <gs...@gmail.com>wrote:
>>
>> > While probably not a big deal, shouldn't the initial element in the
>> array
>> > mt
>> > be 'anded' by 0xffffffffL?
>> >
>> > mt[0]= (int) longMT & 0xffffffffL;
>> >
>>
>
>
Re: [math] MersenneTwister question
Posted by Greg Sterijevski <gs...@gmail.com>.
Yes, you seem to have a good point. My bad.
On Mon, Aug 29, 2011 at 12:50 AM, Ted Dunning <te...@gmail.com> wrote:
> Why?
>
> Isn't that what casting as an (int) does?
>
> On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
> <gs...@gmail.com>wrote:
>
> > While probably not a big deal, shouldn't the initial element in the array
> > mt
> > be 'anded' by 0xffffffffL?
> >
> > mt[0]= (int) longMT & 0xffffffffL;
> >
>
Re: [math] MersenneTwister question
Posted by Ted Dunning <te...@gmail.com>.
Why?
Isn't that what casting as an (int) does?
On Sun, Aug 28, 2011 at 10:17 PM, Greg Sterijevski
<gs...@gmail.com>wrote:
> While probably not a big deal, shouldn't the initial element in the array
> mt
> be 'anded' by 0xffffffffL?
>
> mt[0]= (int) longMT & 0xffffffffL;
>