[Pycrc-users] PyCrc 0.8.1 - bad code for CRC-5, CRC-7 and table index width 4?

[Radosław G. <ra...@he...>]

Hi,

I'm trying to generate table based code for CRC-5 and pycrc-0.8.1
generates code that produces different CRC for most data when
I'm using --alogrithm-tbl --table-idx-width=4.
I am getting similar results for CRC-4, CRC-6 and CRC-7.

Am I doing something wrong or I have found bug in pycrc?

Thanks in advance for your help.

My code is:

================================== main.c ============================
#include <stdio.h>
#include "crcbbf.h"
#include "crcidx4.h"
#include "crcidx8.h"

int main(int argc,char * argv)
{

     crc5_bbf_t bbf;
     crc5_idx4_t idx4;
     crc5_idx8_t idx8;
     #define data_len 1


     unsigned char data[data_len] = { 0x01 } ;//, 0x02 , 0x03 , 0x44};


     int i;
     for (i=0;i<256;i++)
     {
         data[0]=i;

         bbf= crc5_bbf_init();
         bbf= crc5_bbf_update(bbf, data, data_len);
         bbf= crc5_bbf_finalize(bbf);

         idx4= crc5_idx4_init();
         idx4= crc5_idx4_update(idx4, data, data_len);
         idx4= crc5_idx4_finalize(idx4);

         idx8= crc5_idx8_init();
         idx8= crc5_idx8_update(idx8, data, data_len);
         idx8= crc5_idx8_finalize(idx8);
         if ( (bbf != idx4 ) || (bbf != idx8) )
         {
             printf("data[]={0x%02x} bbf=0x%02x, idx4=0x%02x,"
                    "idx8=0x%02x\n", data[0],bbf, idx4, idx8);
         }
     }
     return 0;
}

=============== Script that generates and compiles code ==============
#!/bin/bash
model="--poly=5 --width=4 --xor-in=0 --xor-out=0"
model="$model --reflect-in=0 --reflect-out=0"

../pycrc.py --algorithm=tbl --table-idx-width=4 $model\
   --std=C99 --symbol-prefix=crc5_idx4_ --generate=c \
   --o crcidx4.c

../pycrc.py --algorithm=tbl --table-idx-width=4 $model\
   --std=C99 --symbol-prefix=crc5_idx4_ --generate=h \
   --o crcidx4.h

../pycrc.py --algorithm=tbl --table-idx-width=8 $model\
   --std=C99 --symbol-prefix=crc5_idx8_ --generate=c \
   --o crcidx8.c

../pycrc.py --algorithm=tbl --table-idx-width=8 $model\
   --std=C99 --symbol-prefix=crc5_idx8_ --generate=h \
    --o crcidx8.h

../pycrc.py --algorithm=bbf $model\
   --std=C99 --symbol-prefix=crc5_bbf_  --generate=c \
   --o crcbbf.c

../pycrc.py --algorithm=bbf $model\
   --std=C99 --symbol-prefix=crc5_bbf_  --generate=h \
   --o crcbbf.h

gcc -c crcidx4.c
gcc -c crcidx8.c
gcc -c crcbbf.c
gcc -c main.c
gcc -o main main.o crcbbf.o  crcidx8.o crcidx4.o
./main | head
================================== Output ============================
data[]={0x10} bbf=0x1a, idx4=0x00,  idx8=0x1a
data[]={0x11} bbf=0x1f, idx4=0x05,  idx8=0x1f
data[]={0x12} bbf=0x10, idx4=0x0a,  idx8=0x10
data[]={0x13} bbf=0x15, idx4=0x0f,  idx8=0x15
data[]={0x14} bbf=0x0e, idx4=0x14,  idx8=0x0e
data[]={0x15} bbf=0x0b, idx4=0x11,  idx8=0x0b
data[]={0x16} bbf=0x04, idx4=0x1e,  idx8=0x04
data[]={0x17} bbf=0x01, idx4=0x1b,  idx8=0x01
data[]={0x18} bbf=0x17, idx4=0x0d,  idx8=0x17
data[]={0x19} bbf=0x12, idx4=0x08,  idx8=0x12
=======================================================================
My system is Debian 7.2 (gcc4.7):

radekg@debian64:~/pycrc-0.8.1/crctest$ uname -a
Linux debian64 3.2.0-4-amd64 #1 SMP Debian 3.2.51-1 x86_64 GNU/Linux
radekg@debian64:~/pycrc-0.8.1/crctest$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5' 
--with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs 
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr 
--program-suffix=-4.7 --enable-shared --enable-linker-build-id 
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext 
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu 
--enable-libstdcxx-debug --enable-libstdcxx-time=yes 
--enable-gnu-unique-object --enable-plugin --enable-objc-gc 
--with-arch-32=i586 --with-tune=generic --enable-checking=release 
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Debian 4.7.2-5)

Best Regards

-- 
Radosław Gancarz                             r a d e k g @ h e l l . p l