Buying ships: n_price

       Name: n_price                                                 [Show more]
       Type: Subroutine
   Category: Buying ships
    Summary: Set K(0 1 2 3) to the price of a given ship
  Deep dive: Buying and flying ships in Elite-A
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * n_buyship calls n_price


 This routine fetches the ship price from the new_price table, where prices are
 stored in the standard little-endian manner of 6502 assembly (i.e. using an
 EQUD), and copies it in to K(0 1 2 3), which is a big-endian number like the
 CASH variable.


 Arguments:

   Y                    The ship type number, in the range 0 to 14, as defined
                        in the new_ships table


.n_price

 LDX new_offsets,Y      \ Set X to the offset, measured from new_price, for this
                        \ ship's details block, so X now points to the offset of
                        \ the ship's price in the new_ships table

 LDY #3                 \ Each ship price consists of exactly four bytes (as it
                        \ is a 32-bit number), so set Y = 3 to act as a byte
                        \ counter in the following loop

.n_lprice

 LDA new_price,X        \ Set A to X-th byte of the ship's price from the
                        \ new_ships table

 STA K,Y                \ Store it in the X-th byte of K(0 1 2 3)

 INX                    \ Increment X to point to the next price byte

 DEY                    \ Decrement the byte counter

 BPL n_lprice           \ Loop back to copy the next byte until we have copied
                        \ all 4 of them

 RTS                    \ Return from the subroutine