5 Comment on Implementations

All 16-bit x 16-bit = 32-bit functions implemented here start by clearing the R2 register, which is just used as a “dummy” register with the “add with carry” (ADC) and “subtract with carry” (SBC) operations. These operations do not alter the contents of the R2 register. If the R2 register is not used elsewhere in the code, it is not necessary to clear the R2 register each time these functions are called, but only once prior to the first call to one of the functions.