RE: [boost] Re: CRC review

From: Joe Mariadassou (JMariadassou_at_[hidden])
Date: 2001-03-11 18:26:02

In MSVC :
 k=0;
 k=(~k)<<32;
yields k== 0xffffffff.
Howvever
  k=0;
  k=(~k)<<31<<1;
yields 0 as expected.
So crc_32 works with this fix. But 
crc_16_fast still yields 0x2189
joe 

> -----Original Message-----
> From: Daryle Walker [mailto:darylew_at_[hidden]]
> Sent: Monday, 12 March 2001 7:42 AM
> To: boost_at_[hidden]
> Subject: [boost] Re: CRC review
> 
> 
> [Since I get the daily digest, I didn't see John's 
> attachments.  This is
> written before I looked for them.]
> 
> on 3/10/01 7:59 AM, John Maddock at John_Maddock_at_[hidden] wrote:
> 
> > I'm getting several problem with the crc review code, first 
> the compile
> > time problems:
> > 
> > crc.hpp doesn't build with either VC6 or C++ Builder, I've 
> attatched a
> > modified header file that fixes this, the changes are:
> > 
> > inconsistent use of class and struct (VC6)
> 
> Just noticed that inconsistency in "bit_traits," whoops.
> 
> > use of integral constant expressions not supported by C++ Builder.
> > use of static constant data members changed to 
> BOOST_STATIC_CONSTANT (for
> > VC6).
> 
> I saw this new addition after I downloaded Boost 1.21.0.  I 
> was wondering if
> I should upload a new version of CRC with this change.  But I 
> wouldn't have
> made it before the review period began.  Should I reconsider?
> 
> > I also see the following compiler warnings from Borland:
> > 
> > [C++ Warning] CRC.HPP(92): W8055 Possible overflow in shift 
> operation
> > [C++ Warning] CRC.HPP(95): W8055 Possible overflow in shift 
> operation
> > 
> > And these do look justified to me ??
> 
> You're talking about how I created the "sig_bits_" constants, 
> right?  I'm
> not sure what your warnings exactly mean, but I think that 
> the bits are
> supposed to be overflowing.  I created those constants differently in
> previous versions of the package.  I changed it after Joel 
> Young noticed
> problems with the old method.
> 
> > At run time, VC6 asserts over the following:
> > 
> > // Simulate CRC-16
> > crc_slow<16>  crc_16( 0x8005, 0, 0, true, true );
> > crc_16( data, data + data_len );
> > assert( *crc_16 == 0xBB3D );
> > 
> > and from Borland over:
> > 
> > // Simulate CRC-32
> > crc_slow<32>  crc_32( 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, 
> true, true );
> > crc_32( data, data_len );
> > assert( *crc_32 == 0xCBF43926 );
> > 
> > Looks like the warnings were justified after all?
> 
> All of these tests worked out for me.  Have you checked to 
> see what the
> actual (wrong) numbers were?  Maybe the constants, on the right of the
> equals operators, are written wrong.  I mean as the compiler picked an
> incompatible type for them.  I originally wanted to use 
> macros like UINT32_C
> in <boost/cstdint.hpp>, but they're not #defined on my 
> system(!), so I left
> them bare.
> 
> A few weeks ago, Jens Maurer reported some minor 
> compatibility problems with
> unsigned types in GCC.  It seems that not even the basic 
> unsigned operations
> are that portable.  Ugh.
> 
> > That's all for now, more to come...
> 
> -- 
> Daryle Walker
> Mac, Internet, and Video Game Junkie
> darylew AT mac DOT com
> 
> 
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