Skip to navigation

⌂ ∞ Elite on the BBC Micro and NES

Maths (Arithmetic): MCASH

[NES version, Bank 0]

       Name: MCASH                                                   [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Add an amount of cash to the cash pot

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BuyAndSellCargo calls MCASH
             * DEBRIEF calls MCASH
             * EQSHP calls MCASH
             * Main flight loop (Part 12 of 16) calls MCASH
             * refund calls MCASH
             * LCASH calls via TT113




 Add (Y X) cash to the cash pot in CASH. As CASH is a four-byte number, this
 calculates:

   CASH(0 1 2 3) = CASH(0 1 2 3) + (Y X)



 Other entry points:

   TT113                Contains an RTS



.MCASH

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 TXA                    ; Add the least significant bytes:
 CLC                    ;
 ADC CASH+3             ;   CASH+3 = CASH+3 + X
 STA CASH+3

 TYA                    ; Then the second most significant bytes:
 ADC CASH+2             ;
 STA CASH+2             ;   CASH+2 = CASH+2 + Y

 LDA CASH+1             ; Then the third most significant bytes (which are 0):
 ADC #0                 ;
 STA CASH+1             ;   CASH+1 = CASH+1 + 0

 LDA CASH               ; And finally the most significant bytes (which are 0):
 ADC #0                 ;
 STA CASH               ;   CASH = CASH + 0

 CLC                    ; Clear the C flag, so if the above was done following
                        ; a failed LCASH call, the C flag correctly indicates
                        ; failure

.TT113

 RTS                    ; Return from the subroutine