long_by_long_mulhi() rewritten and commented

[Christian Thalinger]

On Mon, 2009-02-02 at 08:42 -0800, Chuck Rasbold wrote:
> Christian -
> 
> I think your suggested change with attribution to Hacker's Delight is
> a good idea. C2 already references that source elsewhere.

Good.

> 
> I would change the constants in the comments to match those used in
> the building the ideal graph. Then note in a single place that you
> adjusted Warren's algorithm to 64 bits.

Yeah.  Andrew Haley also said today on IRC that it's a bit confusing.
Should I create a CR, make the changes and upload a webrev?

-- Christian