Maths (Arithmetic): DV41

       Name: DV41                                                    [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Calculate (P R) = 256 * DELTA / A
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * STARS2 calls DV41


 Calculate the following division and remainder:

   P = DELTA / A

   R = remainder as a fraction of A, where 1.0 = 255

 Another way of saying the above is this:

   (P R) = 256 * DELTA / A

 This uses the same shift-and-subtract algorithm as TIS2, but this time we
 keep the remainder.


 Returns:

   C flag               The C flag is cleared


.DV41

 STA Q                  \ Store A in Q

 LDA DELTA              \ Fetch the speed from DELTA into A

 JMP DVID4              \ Jump to DVID4 to do:
                        \
                        \   (P R) = 256 * A / Q
                        \         = 256 * DELTA / A
                        \
                        \ and return from the subroutine using a tail call