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In modwrap semantics (also called modulo arithmetic), integer values "wrap round." That is, adding one 1 to MAX produces MIN. This is the defined behavior for unsigned integers in the C standard Standard [ISO/IEC 9899:2011], Section 6.2.5, paragraph 9. This It is frequently the behavior of signed integers, as well. However, it is more sensible in many applications to use saturation semantics instead of modwrap semantics. For example, in the computation of a size (using unsigned integers), it is often better for the size to stay at the maximum value in the event of overflow rather than suddenly becoming a very small value.
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Another technique for avoiding integer overflow is to use only half the range of signed integers. For example, when using an int, use only the range [INT_MIN/2, INT_MAX/2]. This has been a trick of the trade in Fortran for some time, and now that optimizing C compilers are more sophisticated, it can be valuable in C.
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Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Include Page | LDRA_V | LDRA_V | 488 S | Partially implemented.||||||
Compass/ROSE |
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| Could detect violations of this recommendation by flagging any comparison expression involving addition that could potentially overflow. For example, instead of comparing | ||||||
| 488 S | Partially implemented. | |||||||
| PRQA QA-C |
| 0272 (I) | Partially implemented. |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
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| Numeric conversion errors |
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| [FLC] |
Bibliography
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