You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 40 Next »

Programmers frequently make errors regarding the precedence rules of operators due to the unintuitive low-precedence levels of &, |, ^, <<, and >>. Mistakes regarding precedence rules can be avoided by the suitable use of parentheses. Defensive use of parentheses, if not taken to excess, also improves code readability. The precedence of operations by the order of the subclauses are defined in the Java Tutorials [[Tutorials 08]].

The recommendation EXP09-J. Do not depend on operator precedence while using expressions containing side-effects advises against depending on parentheses for specifying the evaluation order, however this advice is applicable only to expressions that contain side-effects.

Noncompliant Code Example

The intent of the expression in this noncompliant code example is to add the variable OFFSET with the result of the bitwise AND between x and MASK.

public static final int MASK = 1337;
public static final int OFFSET = -1337;

public static int computeCode(int x) {
  return x & MASK + OFFSET;
}

According to the operator precedence rules, the expression is parsed as:

x & (MASK + OFFSET)

This expression gets evaluated as shown below, resulting in the value 0.

x & (1337 - 1337)

Compliant Solution

In this compliant solution, parentheses are used to ensure that the expression evaluates as expected.

public static final int MASK = 1337;
public static final int OFFSET = -1337;

public static int computeCode(int x) {
  return (x & MASK) + OFFSET;
}

Exceptions

EXP00-EX1: Mathematical expressions that follow algebraic order do not require parentheses. For instance, consider the expression:

x + y * z

By mathematical convention, multiplication is performed before addition. Consequently, parentheses may prove to be redundant in this case.

x + (y * z)

Risk Assessment

Mistakes regarding precedence rules may cause an expression to be evaluated in an unintended way. This can lead to unexpected and abnormal program behavior.

Recommendation

Severity

Likelihood

Remediation Cost

Priority

Level

EXP09- J

low

probable

medium

P4

L3

Related Vulnerabilities

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

Other Languages

This rule appears in the C Coding Standard as EXP00-C. Use parentheses for precedence of operation.

This rule appears in the C++ Secure Coding Standard as EXP00-CPP. Use parentheses for precedence of operation.

References

[[Tutorials 08]] Expressions, Statements, and Blocks, Operators
[[ESA 05]] Rule 65: Use parentheses to explicitly indicate the order of execution of numerical operators


EXP05-J. Be aware of integer promotions in binary operators      04. Expressions (EXP)      EXP08-J. Understand the evaluation of expressions containing non short-circuit operators

  • No labels