MCPP bug: conditional operator expression

[beamer145]

There is a bug in the evaluation of the conditional operator when it is used as the right hand side argument of an == or != test in a #if.
I can't see any logic in its behaviour, see code examples….

Code examples:
#if  ( ( 1 ? 1 : 0 ) == 10 )
#pragma message_test1NOK
#else
#pragma message_test1OK
#endif

#if  (10 == ( 1 ? 1 : 0 ) )
#pragma message_test2NOK
#else
#pragma message_test2OK
#endif

#if  (10 == ( 1 ? 10 : 0 ) )
#pragma message_test3OK
#else
#pragma message_test3NOK
#endif

Output:
pragma 'message_test1OK'
pragma 'message_test2NOK'
pragma 'message_test3NOK'

[Eric Smith]

Just in case anyone else finds this via a search engine, the bug is a typo in the eval_signed function in mcpp_eval.c. The line:

   v1 = (--*valpp)->val ? v1 : v2;

should read

   valp--; v1 = (valp->val) ? v1 : v2;

because later in the code the value of valpp is updated from valp. The eval_unsigned function has this right already.