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Why does PolySpace 5.1.1 (R2008a) show a red non-terminating loop (NTL) check in my code?

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Asked by MathWorks Support Team
on 27 Jun 2009

My C code looks as follows. When I run a PolySpace verification, the "for" keyword that is mentioned in the comments is marked red with a message that the loop never terminates. Also, I get another red check for a underflow error. I am using the option "-detect-unsigned-overflows".

int main () {
    int intC;
    unsigned int uintA, uintB, i = 0;
    uintA = 20;
    uintB = 30;
    intC = 10;
    // The following keyword "for" is marked with
    // a red NTL check.
    for(i; i < 10; i++) {
      // Subtraction marked with a red UNFL check
      // for a possible underflow.
      if ((uintA - uintB) < uintC) { // UNFL: 20 - 30
        //...
      }
    }
}

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1 Answer

Answer by MathWorks Support Team Sarafina Sarafina BlackTan BlackTan O'Neill BlackTan O'Neill Sarafina BlackTan O'Neill Sarafina O'Neill O'Neill on 27 Jun 2009
  Accepted Answer

The red NTL check is caused by the red underflow check (UNFL) within the loop. Correcting the code that causes the UNFL check or removing the option "-detect-unsigned-overflows" will cause the NTL check to disappear.

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