I need to implement an logarithm function on an 18F part that executes as
quickly as possible.  Essentialy I need to convert power in nW to dBm with
an resolution of 0.01dBm. i.e. 1E6nW (1mW) would return a value of 100
(1dBm).  Both input and output of the function are 24bit integers.

An interpolated table (like Scott Dattalos example) is the obvious choice,
but I wondered if there was an alternative?

Calculating the integer portion of a number in LOG base 2 is trival, it's
simply the bit position of the most singificant bit which is set.  Can this
be extended to the the lower bits to get more accuracy?  If so my equation
boild down to LOG2(nW) * 301.03 - 6000, obviously the constants will have to
be scaled to suit the fixed point output of the LOG2 function.

Thanks for any assistance with this.

Regards

Mike Rigby-Jones

=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
_______________________________________________
http://www.piclist.com
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist