The C programming language provides the ability to use floating-point numbers for calculations. The C Standard specifies requirements on a conforming implementation for floating-point numbers but makes few guarantees about the specific underlying floating-point representation because of the existence of competing floating-point systems.
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On 64-bit Linux, with GCC compiler 4.1, it produces
| Code Block |
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Float is 0.33333334326744079589843750000000000000000000000000 |
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When compiled on an IA-32 Linux machine with GCC compiler 3.4.4 at optimization level 1 or higher, or on an IA-64 Windows machine with Microsoft Visual Studio 2012 in Debug or Release mode, this code prints
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On an IA-32 Linux machine with GCC compiler 3.4.4 with optimization turned off, this code prints
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Failing to understand the limitations of floating-point numbers can result in unexpected computational results and exceptional conditions, possibly resulting in a violation of data integrity.
Recommendation | Severity | Likelihood |
|---|
Detectable | Repairable | Priority | Level |
|---|---|---|---|
FLP00-C | Medium | Probable | No |
No | P4 | L3 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CodeSonar |
| LANG.ARITH.FMULOFLOW LANG.ARITH.FPEQUAL | Float multiplication overflow Floating point equality | ||||||
| ECLAIR |
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| CC2.FLP00 | Fully implemented | ||||||||
| Helix QAC |
| C0275, C0581, C1490, C3339, | |||||||
| Parasoft C/C++test |
| CERT_C-FLP00-a | Floating-point expressions shall not be tested for equality or inequality | ||||||
| PC-lint Plus |
| 777, 9252 | Partially supported | ||||||
| CERT C: Rec. FLP00-C | Checks for absorption of float operand (rec. partially covered) |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this recommendation on the CERT website.
Related Guidelines
| SEI CERT C++ |
| Coding Standard | VOID FLP00-CPP. Understand the limitations of floating-point numbers |
FLP35-CPP. Take granularity into account when comparing floating-point values |
| CERT Oracle Secure Coding Standard for Java |
| NUM53-J. Use the strictfp modifier for floating-point calculation consistency across platforms | |
| ISO/IEC TR 24772:2013 | Floating-point Arithmetic [PLF] |
Bibliography
| [Gough 2005] | Section 8.6, "Floating-Point Issues" |
| [ |
| Hatton 1995] | Section 2.7.3, "Floating-Point Misbehavior" |
| [IEEE 754 2006] | |
| [Lockheed Martin 2005] | AV Rule 202, Floating-point variables shall not be tested for exact equality or inequality |
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