Re: [Lcms-user] Build warnings on OSX / clang

[Noel C. <NCa...@Pr...>]

For what it's worth I saw both your recent messages, Philip.  It's kind
of up to Marti whether he wants to tweak that code to make it not emit a
warning.

 

Indeed those instructions are mixing unsigned and signed values (e.g.,
under some runtime conditions the signed cmsS1Fixed14Number values in
l1, l2, l3 could be assigned to the unsigned cmsUInt32Number variables
ri, gi, bi.  Interestingly, Visual Studio's C++ compiler does not flag
that as a warning...  It's possible it has figured out that the code
does not logically allow a signed negative value to be copied to an
unsigned lvalue.

 

In any case, for other compilers a change that's valid everywhere using
casting to work around this warning would be to code the following:

 

    // Now we have to clip to 0..1.0 range

    ri = (l1 < 0) ? 0 : ((l1 > 16384) ? 16384U : (cmsUInt32Number) l1);

    gi = (l2 < 0) ? 0 : ((l2 > 16384) ? 16384U : (cmsUInt32Number) l2);

    bi = (l3 < 0) ? 0 : ((l3 > 16384) ? 16384U : (cmsUInt32Number) l3);

 

An anecdote:  On the advice of Bob Friesenhahn who a few days ago
suggested building things with multiple compilers to check code, I've
been doing that with our in-house products lately...  

 

We hadn't thought to take the time to do that before.  Specifically,
we're rebuilding our Visual Studio C++ projects with clang and the -Wall
option, and sure enough it's uncovered several bona fide bugs that had
escaped the notice of Visual Studio's compiler alone.  I guess they all
have some blind spots!

 

Many thanks for the idea, Bob!

 

-Noel