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Re: [avr-gcc-list] linear regression on 128L

From: E. Weddington
Subject: Re: [avr-gcc-list] linear regression on 128L
Date: Mon, 04 Apr 2005 11:22:45 -0600
User-agent: Mozilla Thunderbird 0.7.3 (Windows/20040803)

intiha Ho gai wrote:

Hi, Having found out that the avr-gcc lib supports floats and handles them
quite gracefully, I tried porting my linear regression code from
desktop on to the atmega 128L, more or less as is. For testing i used
the same table of X and Y values as sample inputs to the algorithm.

Now I am using microsecond granularity as input to the regression
engine and since the values are fairly large - and since there are sum
of products- I get fairly large numbers (If i do the same on my
desktop, the biggest number i get is sumXSq=7260107358192.000000). Now
I know that doubles are 4 bytes - and i was thinking that would not be
enough - Any way around this?.

Btw when i do print the same result over the serial port (from my
embedded port) I get something like sumXSq=7260108000000.000000 - same
but with 6 of the last significant decimal points lost after
rounding). Any suggestions? Please note that currently optimization
isnt an issue, I just want to get it to run and even if it monstrously
slow, I just have to do this once every boot up!

We would need a volunteer to write the support for 8-byte doubles which would be the math routines in avr-libc, and probably some low-level math routines in GCC (libgcc).

Without this, all that is available is the 4 byte doubles/floats that you're using now.


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