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digitalReadFast() has issues

The macro digitalReadFast() does not work.
I found two issues:

  • For some reason the __builtin_constant_p(P) always returns true when used in a ternary.
  • The _BIT_READ() macros expects a bit number but is being passed a bit mask.

Here is a digitalReadFast() that I've tested:


#define digitalReadFast(P)         \
({                                     \
    int rval;                          \
    if (__builtin_constant_p(P))       \
    {                                  \
    rval = *(_dpin_to_inp_macro(P)) & ( _dpin_to_bitmask_macro(P)) ? HIGH : LOW; \
    }                                  \
    else                               \
    {                                  \
        rval = digitalRead((P));       \
    }                                  \
    rval; \
})

It uses some gcc cpp extensions which allow creating temporary locals, and returning a value from the macro. The temporary local should be optimized out.

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