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Date: 6 Sep 2001 19:28:15 -0000
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From: Morten Welinder <terra@diku.dk>
To: linux-kernel@vger.kernel.org, torvalds@transmeta.com
Subject: Type checking MIN with standard interface
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All the silent-cast properties of integer types do not apply to
pointers.  Therefore...

-----------------------------------------------------------------------------

cub:~> gcc -O2 -Wall min.c
min.c: In function `main':
min.c:19: warning: comparison of distinct pointer types lacks a cast


cub:~> gcc -O2 -Wall kernel-source.c 2>&1 | \
        grep "comparison of distinct pointer types lacks a cast" | \
        find-and-shoot-programmer

:-)

Morten


-----------------------------------------------------------------------------

#include <stdio.h>

#define MIN(x,y)                                \
  ({ const typeof(x) _x = x;                    \
     const typeof(y) _y = y;                    \
                                                \
     (void) (&_x == &_y);                       \
                                                \
     _x < _y ? _x : _y;                         \
  })

int
main ()
{
  /* Good: */
  printf ("%d\n", MIN((signed)1, (signed)1));

  /* Bad: */
  printf ("%d\n", MIN((signed)1, (unsigned)1));

  return 0;
}

-----------------------------------------------------------------------------