Subject:
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Re: FW: Something else is needed, I think...
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 4 May 1999 18:43:29 GMT
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Original-From:
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John A. Tamplin <jat@liveonthenet%AvoidSpam%.com>
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Viewed:
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1070 times
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On Tue, 4 May 1999, Kekoa Proudfoot wrote:
> > - Floating point is not optional. You may reduce the precision to a few
> > bits, or do a few hacks instead of a full blown floating point support,
> > but we definitely need some sort of floating point. If you want a bot
> > that keeps track of it's position, you need it (you also need at least a
> > sin() function/lookup table). Just one example.
>
> My take on this is that you can use fixed point if you really need extra
> decimal places. That is, work in fractions, not whole numbers.
Remember that a floating point number is still stored as "integers" in RAM
and simply represents m*2^e where m is the mantissa and e is the exponent.
FP is useful when you need to represent a wide range of values, since you
can have 24 bits of precision located anywhere throughout the range (in
IEEE 32-bit floats). If you need precision in a range that doesn't vary
much, using fixed-point math is superior since you aren't wasting bits
on the exponent. Ie, treat your 32-bit integer as having a decimal after
16 bits.
> Providing sin() is difficult because of the tradeoff between memory usage
> and usability. My thoughts are that the cost of memory usage outweighs the
> benefit of having the functions available for the few (?) that will use
> them.
It depends on the resolution required. A sin() table with quarter-degree
resolution is under 700 bytes (store 0-45 and compute the others from that
value). Computing sin() on the fly doesn't take much space, but takes time
(typically about 12 multiply/adds depending on the approximation).
John A. Tamplin Traveller Information Services
jat@LiveOnTheNet.COM 2104 West Ferry Way
256/705-7007 - FAX 256/705-7100 Huntsville, AL 35801
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | Re: FW: Something else is needed, I think...
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| (...) Do you mean, when a timer reaches a certain value, run a specified task? Can't you do this already, or is something broken with the current firmware in this regard? (It seem that some combination of wait and start_task should do the trick, (...) (26 years ago, 4-May-99, to lugnet.robotics)
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