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Maximal min() and max()

[LWN subscriber-only content] Like many projects written in C, the kernel makes extensive use of the C preprocessor; indeed, the kernel's use is rather more extensive than most. The preprocessor famously has a number of sharp edges associated with it.

The goal was to increase correctness, but the immediate effect was to break compilation throughout the kernel; the result was a classic linux-kernel flame war of the type that, fortunately, tends not to happen anymore. Even if one expects a large expansion, though, the actual amount may lead to significant eyebrow elevation: the single line of code shown above expands to 47MB of preprocessor output. He converted a number of the worst expansion cases to use the new macros just prior to the 6.11-rc1 release, then merged a patch taking away the ability for min() and max() to work as part of a constant expression.

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