[Novalug] [OT] Question for computer scientist
James Ewing Cottrell 3rd
JECottrell3@Comcast.NET
Mon Feb 2 18:37:29 EST 2009
As Greg mentioned, powers of 2 are trivial: just a shift count. But to
answer your question in the general case, say, 3, should be obvious: a
lookup table is generally faster than actual multiplication, and
especially division.
In any case, using left shift for multiplication and right shift for
division should be a big win. Avoiding floating point under any
circumstances is even better.
JIM
Bonnie Dalzell wrote:
> If you have a value you are using a lot in a program - in this case
> powers of 2 (2^n and 1/2 to the n). Is it easier on the system (or
> faster) to compute them when you need them or fetch them from a
> premade look up table?
>
> I ask this because I am working on a program to compute coefficients of
> inbreeding and the closed source compiled dos program I have been using
> seems to have a look up table file that it uses in relation to coi and I
> think - examining the table in a hex editor that it is powers of two
> precalculated.
>
> I do not have access to the source code for the old dos program. but i
> have been running it to check and see if the calcs of the value
> generated by my program are correct.
>
> No one seems to have published a numerical recipe for calculating
> coefficient of inbreeding anyplace i can find via google so I (a
> non-mathematician) am trying to come up with one.
>
> I have also decided if I get one (numerical recipe) that works it is going
> onto the web as is the program. Since the program is in perl it is by
> defiition open source.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Bonnie Dalzell, MA
> mail:5100 Hydes Rd PO Box 60, Hydes,MD,USA 21082-0060|EMAIL:bdalzell@qis.net
>
> freelance anatomist, vertebrate paleontologist, writer, illustrator, dog
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