Maths (Arithmetic): MCASH

       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:
             * DEBRIEF calls MCASH
             * EQSHP calls MCASH
             * Main flight loop (Part 12 of 16) calls MCASH
             * refund calls MCASH
             * TT210 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

 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