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MSP430 V4.1.0 no compiler warning for comparison between signed and unsigned integers

Danimal
Expert 1135 points


 The TI compiler does not give a warning due to the comparison between signed and unsigned integers.

Why?

This same code compiled using other compilers such as the visual C compiler will generate a warning.

Is there a way to have the compiler generate a diagnostic warning message?

static unsigned long
foo(void) {
 int i=-1;
 unsigned int j = 100;
 volatile unsigned long gt = 0;
 volatile unsigned long lte = 0;

  while ( i != 0) {
    if ( i > j) {
       gt++;
    } else {
       lte++;
     }
     i--;
  }

  return gt;
}

 

The following web location lists all the available diagnostic warning/errors/ remarks messages output by the TI 3.2 version of the compiler. http://processors.wiki.ti.com/images/6/60/TICompiler_MSP430_ErrorList.pdf

There is no compiler warning for a "comparison between signed and unsigned integers" listed.

Just a recommendation, This list may prove to be more useful as an appendix in the slau132g "MSP430 Optimizing C/C++ compiler user's guide".

  • 0
    Guru 227245 points

    Why should you get a warning when comparing a value with a value? The comparison is perfectly valid.
    If you would do a "if j >=0" you'd get an 'expression is always true' or for "if (j<0)" an 'expression is always false' warning. Same for "if (i>32768)".
    IIRC, in your case, the compiler will cast both, i and j to a signed long and compare them. No problem, no warning needed. But even without the cast, the comparison is doable (just not as straight to implement)

  • 0
    Guru 92251 points

    Danimal said:
    There is no compiler warning for a "comparison between signed and unsigned integers" listed.

    Have you tried enabling checking of Misra Rules 10 - Arithmetic Type Conversions? Under CCS project properties -> Build -> MSP430 Compiler -> Advanced Options -> MISRA-C:2004.

    Previous experience is that the TI compilers themselves don't support as "strict" warnings as other C compilers. But since they support checking of Misra rules, the Misra rules can be enabled to get more "strict" warnings.

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