Function:

Tests the specified bit in the register/memory operand, if it is zero the
Z flag is set otherwise it is cleared. The bit number (CL or immediate)
is ANDed with 07 (for 8-bit operands) or 0F (for 16-bit operands) to get a
valid bit number.

The first (smaller) clock count in each pair is for register operands.
Note that 0F is treated as <POP CS> on the 88/86 and prefixes newer
instructions on 286+.

(Supplied by Anthony Naggs)