Re: computation of square root & reciprocal calculation

frustum@xxxxxxxxxxx wrote:
....
Jim Blinn wrote an article about abuse of float/int casting and gave
some quick and dirty functions for log/exp/x^y etc pretty much along
the lines as appears above, and in fact, that function was probably one
of the ones he gave too. It was in one of his columns that ran in IEEE
CG&A. I'm pretty sure I have the magazine at work; I'd go check, but I
work from home and rarely visit the office. I think I subscribed to it
from 1992 to 1999, so the article was somewhere in that range of dates.
Even if Jim Blinn didn't have a hand in its creation, his article is
an interesting read and he might give some credit to where he first saw
the trick.

It was in the July/August 1977 edition of IEEE Computer Graphics and
Applications. He doesn't really give credit for where he first saw the
idea (which seems to be par for him). But, as is also par for him, he
describes it all clearly and nothing seems like magic, unlike the code
that started this subthread.

He provides hacks for log2(x), pow2(x), sqrt(x), 1/x, 1/sqrt(x).

If you want a copy, email me at frustum@xxxxxxxxxxx and I'll mail you a
scan of the article. I'd post it online but I don't want to violate
the copyright too badly.

.