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To: David Lecomber <david@streamline-computing.com>
Cc: gdb@sources.redhat.com
Subject: Re: Boolean equality (C++/Fortran)
References: <1094224351.31231.59.camel@cpc4-oxfd5-5-0-cust12.oxfd.cable.ntl.com>
From: Jim Blandy <jimb@redhat.com>
Date: Tue, 07 Sep 2004 17:26:00 -0000
In-Reply-To: <1094224351.31231.59.camel@cpc4-oxfd5-5-0-cust12.oxfd.cable.ntl.com>
Message-ID: <vt2isaqdm9v.fsf@zenia.home>
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David Lecomber <david@streamline-computing.com> writes:

> In valarith.c:value_binop, where v1 and v2 have been established to be
> values of type bool, we have:
> 
>        case BINOP_EQUAL:
>           v = v1 == v2;
>           break;
>           
>         case BINOP_NOTEQUAL:
>           v = v1 != v2;
> 	  break;
> 
> Isn't this wrong?  If you are mixing your compilers, then, at least for
> Fortran, the actual value of true can vary (1 or -1 I have so far
> seen).  For C++ this is less likely to happen, and so far as I can tell
> changing the above would not harm anything.  
> 
> Does anyone have any comments on replacing the above with:
> 
>        case BINOP_EQUAL:
>           v = !((!v1 && v2) || (v1 && !v2));
>           break;
>           
>         case BINOP_NOTEQUAL:
>           v = (!v1 && v2) || (v1 && !v2);
> 	  break;

The general idea looks right.  But how about:

>        case BINOP_EQUAL:
>           v = !v1 == !v2;
>           break;
>           
>         case BINOP_NOTEQUAL:
>           v = !v1 != !v2;
> 	  break;