#pragma is a preprocessor directive that speaks directly to the implementation,
such as the compiler or linker, or possibly the IDE. Check your documentation.

__fastcall is a suggestion to use registers to pass arguments, if possible, instead
of using the stack.

1 << i is 1 shifted i times leftwards. It is equal to 2 to the power of i.

(maskIO & 0x08) is masking bit 3 (2 to the power of 3 is 8).
If bit 3 is set, the result is non-zero (true).

I do not know what a "bit conjunction operator" is (unless it is just &).