[avr-gcc-list] Re: Tables

[David Brown]

David VanHorn wrote:
>  
> How would I construct a lookup table of logarithms in program memory?
> I'll need the logarithm of N entries between 0 and 1, ex:  If N = 10, 
> then I need log(0), log(0.1), log(0.2) etc.
> I don't know what precision I'll need yet, but I'll need to be adjusting 
> N, so manually creating the table with a spreadsheet would be one way, 
> though icky.
> I'm hoping there's a way to have the compiler generate it for me?
>  

Before you get that far, what do you want the logs for?  And what base 
(if it matters)?  And what speed and accuracy?  If you need low speed 
and high accuracy, just use the standard C log function.  If you need 
high speed and low accuracy and low code space, a find-first-one 
function will give you a start.  And if you decide that a table is the 
best answer, consider first normalizing your numbers (unless you are 
using floating point, in which case they are already normalized), and 
consider using a non-linear table.