Re: [boost] CRC library error

From: Vladimir Prus (ghost_at_[hidden])
Date: 2002-09-23 03:57:52

Craig Henderson wrote:
> There is a small problem with the CRC library that is shown up at runtime
> with the MSVC7 compiler option "Smaller Type Check" /RTCc. The problem is in
> crc.hpp at line 550 which reads
> 
> { return x ^ ( rem >> (DoReflect ? 0u : Bits - CHAR_BIT) ); }
> 
> Changing this to
> { return 0xff & (x ^ ( rem >> (DoReflect ? 0u : Bits - CHAR_BIT) ) ); }
> 
> solves the problem.

Hi Graig,
can you tell more about that warning? Is it triggered whenever int 
converted to unsigned char has value larger than 255? In this particular 
case, that's precisely what is desired. Is it possible to suppress this 
warning without adding extra operation --- I'm not sure all compilers 
will optimize it.

BTW, Daryle, I think that the comment to the function 'index' which 
contains this warning:

     // Compare a byte to the remainder's highest byte
     static  unsigned char  index( value_type rem, unsigned char x )

is rather misleading. It's been long since I last looked in CRC, so I 
can't offer better comment off-hand, but I believe "compare" implies 
true or false result, not index into precomputed crc table. What do you 
think?

- Volodya