![]() The upcast technique is the preferred approach when applicable. ![]() This approach can be somewhat more difficult to implement and to audit than either of the other two approaches. The precondition testing technique requires different precondition tests for each arithmetic operation. Consequently, compliant code performs only a single range check just before converting the final result to the original smaller type and throws an ArithmeticException if the final result is outside the range of the original smaller type. The arithmetic operations implemented as methods of this type cannot overflow instead, they produce the numerically correct result. Type BigInteger is the standard arbitrary-precision integer type provided by the Java standard libraries. Convert the inputs into objects of type BigInteger and perform all arithmetic using BigInteger methods. This approach cannot be used for type long because long is already the largest primitive integer type. Downcast the final result to the original smaller type before assigning to a variable of the original smaller type. Note that the range check must be performed after each arithmetic operation larger expressions without per-operation bounds checking can overflow the larger type. Check each intermediate result for overflow of the original smaller type and throw an ArithmeticException if the range check fails. Cast the inputs to the next larger primitive integer type and perform the arithmetic in the larger size. Throw an ArithmeticException when the operation would overflow if it were performed otherwise, perform the operation. Check the inputs to each arithmetic operator to ensure that overflow cannot occur. ![]() Comparison of Compliant Techniquesįollowing are the three main techniques for detecting unintended integer overflow: For operands of opposite signs, this approach can result in integer overflow, consequently violating the compareTo() contract. Consequently, an apparent but incorrect optimization would be to subtract the operands and return the result. The meaning of the return value of the compareTo() method is defined only in terms of its sign and whether it is zero the magnitude of the return value is irrelevant. Failure to account for integer overflow has resulted in failures of real systems, for example, when implementing the compareTo() method. The silent wrap can result in incorrect computations and unanticipated outcomes. When a mathematical operation cannot be represented using the supplied integer types, Java's built-in integer operators silently wrap the result without indicating overflow. Because the () method returns the absolute value of any number, it can also overflow if given the minimum int or long as an argument. set to the minimum or the maximum value in the representable range, rather than wrapped around.Because the ranges of Java types are not symmetric (the negation of each minimum value is one more than each maximum value), even operations such as unary negation can overflow if applied to a minimum value. On some processors like graphics processing units (GPUs) and digital signal processors (DSPs) which support saturation arithmetic, overflowed results would be "clamped", i.e. The C11 standard states that for unsigned integers, modulo wrapping is the defined behavior and the term overflow never applies: "a computation involving unsigned operands can never overflow." In particular, if the possibility has not been anticipated, overflow can compromise a program's reliability and security.įor some applications, such as timers and clocks, wrapping on overflow can be desirable. modulo a power of the radix, usually two in modern computers, but sometimes ten or another radix).Īn overflow condition may give results leading to unintended behavior. ![]() The most common result of an overflow is that the least significant representable digits of the result are stored the result is said to wrap around the maximum (i.e. This is wrapping in contrast to saturating. All digits are set to the maximum 9 and the next increment of the white digit causes a cascade of carry-over additions setting all digits to 0, but there is no higher digit (1,000,000s digit) to change to a 1, so the counter resets to zero. Integer overflow can be demonstrated through an odometer overflowing, a mechanical version of the phenomenon.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |