On 8/15/04 5:34 PM, "Bert Klaps" <bertk@easics.be> wrote:
On Sat, Aug 14, 2004 at 10:44:48PM -0400, Daryle Walker wrote:
On 8/10/04 11:32 AM, "Bert Klaps" <bertk@txc.com> 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?
Sure, though in the end I picked random values for polynomials etc and found that for CRC width or `Bits' < 8 and ReflectIn = false crc_basic and crc_optimal give different results for those as well - crc_basic is correct of course.
Example #1 is a SDH/SONET Low Order LCAS control word with CRC-3 taken from ITU-T G.707 (12/03) XIII.2: That's a 29 bit word protected by a 3 bit CRC, together 32 bits or 4 bytes. The ITU-T text itself has 4 examples which include a correct CRC-3. So the answer to these four sequences should be zero. a. 0x3a 0xc4 0x08 0x06, answer is 0 b. 0x42 0xc5 0x0a 0x41, answer is 0 c. 0x4a 0xc5 0x08 0x22, answer is 0 d. 0x52 0xc4 0x08 0x05, answer is 0 The LCAS CRC-3 parameters are: - polynomial: 0x3 ( x^3 + x + 1 ) - initial remainder: 0 - final xor value: 0 - reflected input: false - reflected remainder: false
Example #2 is a SDH/SONET J0/J1/J2/N1/N2/TR TTI (trace message) with CRC-7, o.a. ITU-T G.707 Annex B, G.832 Annex A: That's basically calculated over 16 bytes: the first input byte is always 0x80, the following 15 bytes are printable characters. Some examples: a. "\x80""123456789ABCDEF" , answer is 0x62 b. "\x80""TTI UNAVAILABLE" , answer is 0x23 The TTI CRC-7 parameters are: - polynomial: 0x9 ( x^7 + x^3 + 1 ) - initial remainder: 0 - final xor value: 0 - reflected input: false - reflected remainder: false
Does anyone know how to add patches to a file? (It looked like it was in a "diff" format.
Plain "diff -c"...
OK, I added the fixes from the original patch, and I added the two test cases above. I'm wondering: do the augmented-CRC functions need similar protection from inappropriate shifting? When I tried the augmented-CRC functions with the new tests, I got (right) shifting warnings. My attempt to generalize the patch fix to the augmented-CRC functions got simultaneous left- and right-shift warnings (so I removed that "fix"). I guess I haven't thought about the problem enough. The affected files would be "crc.hpp" and "crc_test.cpp". -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com