[lwip-devel] [bug #33398] Compiler says 'Pointless Comparison'

[Mike Kleshov]

URL:
  <http://savannah.nongnu.org/bugs/?33398>

                 Summary: Compiler says 'Pointless Comparison'
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: kleshov
            Submitted on: Wed 25 May 2011 13:30:00 MSD
                Category: TCP
                Severity: 2 - Minor
              Item Group: Compiler Warning
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: CVS Head

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Details:

Here is the snippet of code:

#ifndef TCP_LOCAL_PORT_RANGE_START
/* From http://www.iana.org/assignments/port-numbers:
   "The Dynamic and/or Private Ports are those from 49152 through 65535" */
#define TCP_LOCAL_PORT_RANGE_START  0xc000
#define TCP_LOCAL_PORT_RANGE_END    0xffff
#endif
  static u16_t port = TCP_LOCAL_PORT_RANGE_START;

 again:
  if (port++ >= TCP_LOCAL_PORT_RANGE_END) {
    port = TCP_LOCAL_PORT_RANGE_START;
  }

The line with the if statement causes a compiler warning: 'pointless integer
comparison, the result is always true.' The compiler is IAR for ColdFire. Size
of int is 32 bits.
The funny thing is when I change '>=' to '>', it says 'pointless integer
comparison, the result is always false.'
It could be a compiler bug. But still, wouldn't it make sense to change it to
(port++ == TCP_LOCAL_PORT_RANGE_END), like in UDP code? Presumably, port can
never be greater than 0xffff since it's u16_t.




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