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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Quick inverse square root
Date: Mon, 4 Jan 2021 13:13:00 +0100
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On 2021-01-04 12:28, AdaMagica wrote:
> AdaMagica schrieb am Montag, 4. Januar 2021 um 12:13:53 UTC+1:
>>> with INTERFACES; use INTERFACES;
>>> generic
>>> type F is digits <>;
>>> type U is mod <>;
>>> with function SHIFT_RIGHT( n : U; amount : NATURAL ) return U;
>>> function G_QUICK_INVERSE_SQRT( a : F ) return F;
> 
> I haven't got the slightest idea for which range this function should be applied, but for sure not for the complete Float range.
> Thus there should be an assertion about the range of the parameter a in the body. Or even better a precondition in the spec.

It appears to be the Newton method with an heuristic used to choose the 
starting point. The descriptions is here:

    https://en.wikipedia.org/wiki/Fast_inverse_square_root

It also mentions a hack for double precision IEEE 754 floats.

P.S. The method makes no sense to implement or use on modern hardware.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de