Maths (Arithmetic): LL62

       Name: LL62                                                    [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Calculate 128 - (U R)
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * LL9 (Part 8 of 12) calls LL62


 Calculate the following for a positive sign-magnitude number (U R):

   128 - (U R)

 and then store the result, low byte then high byte, on the end of the heap at
 XX3, where X points to the first free byte on the heap. Return by jumping down
 to LL66.


 Returns:

   X                    X is incremented by 1


.LL62

 LDA #128               ; Calculate 128 - (U R), starting with the low bytes
 SEC
 SBC R

 STA XX3,X              ; Store the low byte of the result in the X-th byte of
                        ; the heap at XX3

 INX                    ; Increment the heap pointer in X to point to the next
                        ; byte

 LDA #0                 ; And then subtract the high bytes
 SBC U

 STA XX3,X              ; Store the low byte of the result in the X-th byte of
                        ; the heap at XX3

 JMP LL66               ; Jump down to LL66