The Java Language Specification (JLS), Section 15§15.17.3, "Remainder Operator %" states
The remainder operation for operands that are integers after binary numeric promotion (§5§5.6.2) produces a result value such that (a/b)*b+(a%b) is equal to a. This identity holds even in the special case that the dividend is the negative integer of largest possible magnitude for its type and the divisor is -1 (the remainder is 0). It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative, and can be positive only if the dividend is positive; moreover, the magnitude of the result is always less than the magnitude of the divisor.
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5 % 3 produces 2
5 % (-3) produces 2
(-5) % 3 produces -2
(-5) % (-3) produces -2
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As a result, code that depends upon the remainder operation to always returns return a positive result is erroneous.
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Automated detection of uses of the % operator is straightforward. Sound determination of whether those uses correctly reflect the intent of the programmer is infeasible in the general case. Heuristic warnings could be useful.
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this guideline on the CERT website.
Related Guidelines
C Secure Coding Standard: "INT10-C. Do not assume a positive remainder when using the % operator"
C++ Secure Coding Standard: "INT10-CPP. Do not assume a positive remainder when using the % operator"
Bibliography
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Bibliography#JLS |
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§15.17.3 |
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, "Remainder Operators" | http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.17.3 |
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03. Numeric Types and Operations (NUM) NUM02-J. Avoid performing bitwise and arithmetic operations on the same data