c/10226: unsigned short promotion with bitwise inversion

[Glen Nakamura]

The following reply was made to PR c/10226; it has been noted by GNATS.

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org,
	mmarks@internetmachines.com
Cc:  
Subject: Re: c/10226: unsigned short promotion with bitwise inversion
Date: Wed, 26 Mar 2003 10:06:02 -1000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10226
 > unsigned short A = 0xDEAD;
 > unsigned short B;
 > B = ~A;
 > if ( B == ~A) {
 >    printf("Pass\n");
 > }
 > else {
 >    printf("Fail\n");
 > }
 
 I'll leave the final decision to the language lawyers, but I don't think
 this is a bug in GCC.  The ~ operator is subject to integer promotion,
 so with the implicit conversions the expression becomes:
   if ((int) B == ~((int) A))
 which is indeed false in the example above.
 
 In fact, I see the following warning when compiling with -Wall (GCC 3.3):
 warning: comparison of promoted ~unsigned with unsigned
 
 Perhaps "if (B == (unsigned short) ~A)" will behave as you expect.
 
 - glen