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The C Standard, subclause F.6 states:  [ISO/IEC 9899:2011]. , states:

If the return expression is evaluated in a floating-point format different from the return type, the expression is converted as if by assignment³⁶² to the return type of the function and the resulting value is returned to the caller.

362) Assignment removes any extra range and precision.

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float calcPercentage(float value) {
  return (float)(value * 0.1f);
}

void floatRoutine(void) {
  float value = 99.0f;
  long double percentage;

  percentage = calcPercentage(value);
}

Compliant

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Solution (Alternative)

Unfortunately, not all compilers honor casts. In this case, the range and precision must be forced by assignment to a variable of the correct type. This compliant solution forces the assignment by type-qualifying result as volatile and assigning the result of the floating-point operation to result before returning it:

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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