Re: [boost] problem with small width CRCs

From: Daryle Walker (darylew_at_[hidden])
Date: 2004-08-14 21:44:48

On 8/10/04 11:32 AM, "Bert Klaps" <bertk_at_[hidden]> wrote:

> I ran into a problem using the CRC library for SDH LCAS control words
> (3-bit CRC) and SDH Trail Trace Identifier messages (7-bit CRC).

Could you provide sample data and answer so a new test case can be added?

> For CRC widths smaller than character width the theoretical and
> optimized CRC computers produce different results for non-reflected
> input. Gcc produces this warning:
> 
> /usr/local/boost/boost_1_31_0/boost/crc.hpp:581: warning: right shift
> count >= width of type
> 
> The problem is that for the table based computer the msb of
> the remainder needs to be compared to the msb of the input byte.
> For most popular CRC parameters that's a right shift, but for CRC
> widths smaller than a character this should be a left shift...
> 
> Reflected input requires comparing lsb's which doesn't involve any
> shifting.
> 
> I've attached a patch that solved the problem for me.
[TRUNCATED list of errors and the patch]

Does anyone know how to add patches to a file?  (It looked like it was in a
"diff" format.  Isn't there an automated tool for this, or do I apply the
changes manually?)

Have we branched for release yet?  I don't want to add the changes (to the
main line) until then so I won't risk breaking the release build.

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com