[boost] Re: CRC review

From: John Maddock (John_Maddock_at_[hidden])
Date: 2001-03-14 07:52:38

>I've looked at it.  What's wrong with it?  I'm calling a "const" member
>function of a temporary object; isn't that OK?  I've seen it in some C++
>books, and I use it in crc_fast's constructor.  (I have no choice there
>unless I stop using an initializer list.)

All I know is that gcc chokes over it, sorry :-(

I also found it hard to figure out what was going on at first glance - I
prefer to break things up more but that may be personal preference.

>I'll probably turn that to a test in "crc_test.cpp".

Good idea, BTW I think that the way to fix this for VC6, is to use a
function object rather than a free function, but that probably relegates
reflect to an implementation detail.

>You're missing a parenthesis here; there's supposed to be one after
"Bits."
 
I spotted that afterwards, the problem seems to be that shifting by more
than (or equal to) the number of bits in the value is undefined behaviour -
and this is what messes up Borland C++.

>I don't think there are "standard" CRC parameters.  I picked the ones
above
>as examples because those were the examples used in the Internet papers I
>read.  If I use other types, I would have to compute the "123456789"
>reference CRC result by hand as a check; which isn't easy.  (I took about
a
>half-hour doing the 1-bit example that is in the test.)

That isn't the impression that I got - chosing the wrong parameters can
lead to something that's not as strong as it should be - but maybe some
else can jump in here.

>The unsigned-char version should cover the others by implicit conversion.
>For a name, maybe "process"?

Maybe, it's hard to think of a really good one I admit.

>I hope you haven't reported that last bug.  If so, take it back.  It is
not
>a bug, because "<:" is a perfectly legitimate digraph!  It represents the
>opening square bracket ("[").

Well well, you learn something new every day - just shows how few compilers
support digraphs that only gcc (as far as I know) chokes over this.

- John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/