Re: [eigen] Indexes: why signed instead of unsigned?

[Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>]

On Tue, 11 May 2010, Benoit Jacob wrote:

> What about the other debate, between int (32bit) and ptrdiff_t (same
> size as void*) ?

A disadvantage of the potentially bigger ptrdiff_t is that it costs more 
memory. I guess this is usually not an issue, but it does make a 
difference for sparse matrices. In fact, we earlier had somebody who 
wanted to use 16-bit instead of 32-bit for this reason: 
http://listengine.tuxfamily.org/lists.tuxfamily.org/eigen/2009/02/msg00006.html

The performance hit of using 64-bit indices may not be so big, but we 
never had somebody complain about eigen using only 32-bit indices. And on 
a practical note, it seems rather short before the planned beta tagging to 
make such a radical change.

No opinion on the signed/unsigned debate.


Jitse