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A reviewer could now recognize that the operation should also be checked for overflow. This The need for an overflow check might not have been apparent in the original, noncompliant code example . See rule (see NUM00-J. Detect or prevent integer overflow for more information).
Noncompliant Code Example (Logical Right Shift)
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This noncompliant code example masks off the upper 24 bits of the promoted byte array element before performing the addition. The number of bits required to mask the sizes of byte and int are specified by the JLS The Java Language Specification. Although this code calculates the correct result, it violates this rule by combining bitwise and arithmetic operations on the same data.
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| Code Block | ||
|---|---|---|
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int limit = 0x1FFFF; // 2^17 - 1 = 131071 |
NUM01-J-EX1: Data that is normally treated arithmetically may be treated with bitwise operations for the purpose of serialization or deserialization. This alternative treatment is often required for reading or writing the data from a file or network socket. Bitwise operations are also permitted when reading or writing the data from a tightly packed data structure of bytes.
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Performing bitwise manipulation and arithmetic operations on the same variable obscures the programmer's intentions and reduces readability. Consequently, it is more difficult for a security auditor or maintainer to determine which checks must be performed to eliminate security flaws and ensure data integrity. For instance, overflow checks are critical for numeric types that undergo arithmetic operations but less critical for numeric types that undergo bitwise operations.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
NUM01-J | Medium | Unlikely | Medium | P4 | L3 |
Automated Detection
| Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Parasoft Jtest |
| CERT.NUM01.BADSHIFT CERT.NUM01.NCBAV | Avoid incorrect shift operations Do not perform bitwise and arithmetic operations on the same data |
Related Guidelines
INT14-C. Avoid performing bitwise and arithmetic operations on the same data | |
VOID INT14-CPP. Avoid performing bitwise and arithmetic operations on the same data |
Bibliography
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