Subject:
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Re: NQC v. LegOS / size
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 9 Feb 1999 17:45:02 GMT
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Original-From:
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Ben Laurie <ben@algroup.co.SAYNOTOSPAMuk>
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Viewed:
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1343 times
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dave madden wrote:
>
> =>From: Ben Laurie <ben@algroup.co.uk>
> =>...
> =>Markus L. Noga wrote:
> =>> Apart from the limitations imposed by H8 architecture (an 8/16 bit
> =>> platform with the usual constraints on integer length, available memory
> =>> and library functions), there's mainly one language limitation I am
> =>> aware of.
> =>
> =>Actually, I ran into another - you can divide by numbers that aren't
> =>powers of two. At least, I can't. There seems to be a missing assembler
> =>routine.
>
> Yes, the H8 divide instruction can only do (16 bits)/(8 bits), so GCC
> calls a helper routine when you attempt to divide an integer by
> another integer. (Same thing with multiplication: the hardware can
> only do (8 bits) x (8 bits) -> (16 bits), so GCC often calls a helper
> function for that, too.) Powers of two (division & multiplication)
> can be converted to shifts, and multiplication/division by a constant
> can often be turned into a combination of shifts and adds; GCC will do
> that if it thinks the combination will be more efficient than a
> generalized routine.
I knew that! In my youth I got one up on a Z80 assembler guru by doing a
divide by 80 with shifts and adds faster than his best optimized
version...
> I haven't had need of any complicated math, so I haven't written the
> helper routines; maybe Markus has some. (Alternatively, I believe
> Kekoa identified some math routines in the RCX ROM...it might be
> possible to use those.)
It didn't matter much to me either - I was trying to do a rolling
average, but I didn't mind having 8 on the bottom instead of 10 :-)
Cheers,
Ben.
--
http://www.apache-ssl.org/ben.html
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | Re: NQC v. LegOS / size
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| =>From: Ben Laurie <ben@algroup.co.uk> =>... =>Markus L. Noga wrote: =>> Apart from the limitations imposed by H8 architecture (an 8/16 bit =>> platform with the usual constraints on integer length, available memory =>> and library functions), (...) (25 years ago, 9-Feb-99, to lugnet.robotics)
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