Re: warning: & has lower precedence than ==; == will be evaluated first

[Nick Stoughton]

Interesting!

n & 1 == 1

is the same as n & 1, since "1==1" is always true, which is the value 1. If the bottom bit of n is set, this will evaluate to 1, which is also the value "true". So, while clang is perfectly correct about the problem, the code generated is identical with and without the parentheses. This statement should just be

return (n & 1);

This is simpler to understand, and won't generate spurious warnings. Adding parentheses  like this:

return ((n & 1) == 1) ? true : false;

is a waste of time, confusing, and unnecessary.

-- 

Nick Stoughton

On Wed, Jan 4, 2012 at 7:10 PM, Ryan Schmidt <address@hidden> wrote:

Trying to build groff 1.21 with clang 3.0 (or 2.9) on OS X 10.6.8 I get this warning, which seems like it's pointing out a real problem:


input.cpp:998:13: warning: & has lower precedence than ==; == will be evaluated first [-Wparentheses]
 return (n & 1 == 1) ? true : false;
           ^~~~~~~~
input.cpp:998:13: note: place parentheses around the == _expression_ to silence this warning
 return (n & 1 == 1) ? true : false;
           ^
             (     )
input.cpp:998:13: note: place parentheses around the & _expression_ to evaluate it first
 return (n & 1 == 1) ? true : false;
           ^
         (    )
1 warning generated.


I notice you've had a fix for this in your repository for half a year already. Will you release a new version of groff soon? We would like to benefit from all the improvements you've made in groff since the release of 1.21 one year ago.




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