SEI CERT C Coding Standard

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  • Standard programming model for current (Intel family) PC processors is ILP32.
  • One issue with long in C was that there are both codebases that expect pointer and long to have the same size, while there are also large codebases that expect int and long to be the same size. The compability model LLP64 was designed to preserve long and int compability by introducing a new type to remain compatible with pointer (long long)
  • long long LLP64 is only defined for LLP64the only data model that defines a size for the long long type.
  • LP32 is used as model for the win-16 APIs of Windows 3.1.
  • Most Unixes use LP64, primarily to conserve memory space compared to ILP64. Examples, including: 64-bit Linux, FreeBSD, NetBSD, and OpenBSD.
  • Win64 uses the LLP64 model (also known as P64). This model conserves type compability between long and int, but looses type compability between long and pointer types. Any cast between a pointer and an existing type requires modification.
  • ILP64 is the easiest model to work with, since because it retains all compability with the much used ubiquitous ILP32 model, except specific assumptions that the core types are 32-bit. However this model requires significant memory, and both code and data size significantly increase.

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