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Multiplication result converted to larger type

ID: cpp/integer-multiplication-cast-to-long Kind: problem Security severity: 8.1 Severity: warning Precision: high Tags: - reliability - security - correctness - types - external/cwe/cwe-190 - external/cwe/cwe-192 - external/cwe/cwe-197 - external/cwe/cwe-681 Query suites: - cpp-code-scanning.qls - cpp-security-extended.qls - cpp-security-and-quality.qls

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This rule finds code that converts the result of an integer multiplication to a larger type. Since the conversion applies after the multiplication, arithmetic overflow may still occur.

The rule flags every multiplication of two non-constant integer expressions that is (explicitly or implicitly) converted to a larger integer type. The conversion is an indication that the expression would produce a result that would be too large to fit in the smaller integer type.

Recommendation

Use a cast to ensure that the multiplication is done using the larger integer type to avoid overflow.

Example

int i = 2000000000; long j = i * i; //Wrong: due to overflow on the multiplication between ints, //will result to j being -1651507200, not 4000000000000000000 long k = (long) i * i; //Correct: the multiplication is done on longs instead of ints, //and will not overflow long l = static_cast<long>(i) * i; //Correct: modern C++

References