I read through this in detail... Is it just me, or are these things that are invoked by intentionally bypassing the typing?

I mean, you have to go out of your way and use a cast to get the UB in the first example.

For the `isxdigit` implementation, using a parameter to index into an array without a length check is pretty suspect already. I don't think any of my code actually indexes an array without checking the length in some way.

For the float -> int conversion, converting a float to an int without picking a conversion does not make sense in the first place - math.h has rounding and ceiling functions.

> For all you know the compiler has no internal way to even express your intention here.

I'm human, not a compiler, and even I cannot tell what the intention is behind trying to call NULL as a function. What exactly is expected to happen?

> Because the argument needs to be a pointer, and the NULL macro may be misinterpreted as an integer zero.

I don't think this is true for C. The NULL macro is defined to be a pointer in the C standard, AFAIK. Just because comparisons with zero are allowed, does not imply that the standard implicitly promotes NULL to `int`.

I think only the final one is of note (the 24-bit shift assigned to a uint64_t).

> I don't think this is true for C. The NULL macro is defined to be a pointer in the C standard, AFAIK. Just because comparisons with zero are allowed, does not imply that the standard implicitly promotes NULL to `int`.

Probably confusion with C++ where NULL is 0 which is a special case that can be implicitly cast to both integers and pointers, unlike non-zero constants. C doesn't need this because it doesn't require explicit casts from void pointers to others.