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Message
From: unneback at opencores.org<unneback@o...>
Date: Tue Sep 21 10:56:54 CEST 2004
Subject: [oc] Logs in hardware?
Hi,I did a log2 implementation a couple of years ago. This
implementation is rather rough and not very accurate,
on the other hand it is small and efficient. ;-)
Lets look on a number with 8 bits:
ex=0110_0000 (=96)
we number the bits from 7 downto 0 (left to right)
Lets assume we want the answer to be unsigned binary
number with decimal point on the form nnn.nnnnnnn
Start looking on the bits from left. Find the first bit='1'
In this case ex(7)='0' but ex(6)='1'. This means that
the integer part of the answer is 2^6.
answer = 110.1000000 (=6+64/128=6.5)
If you need log10 instead of log2 multiply with log10(2)
log10(96)=6.5*log10(2)=1.957
Maybe not that accurate but efficient ...
regards
/Michael
----- Original Message -----
From: Michael M Delaney<mmdst23+@pitt.edu>
To:
Date: Mon Sep 20 22:41:41 CEST 2004
Subject: [oc] Logs in hardware?
> Can anyone suggest any websites, books, or papers on how a log is
> actaully
> calcuated? So far, I haven't had much luck with google, and after
> looking
> at the list archives for the FPU, it seems like it was decided that
> doing
> logs and trigs in hardware wasn't worth the time and effort (I
> could be
> wrong, I only took a quick glance through the source).
> Thanks,
> Mike
>
>
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