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⌂ ∞ ▽ Elite on the BBC Micro and NES

Tactics: TACTICS (Part 5 of 7)

[Acorn Electron version]

       Name: TACTICS (Part 5 of 7)                                   [Show more]
       Type: Subroutine
   Category: Tactics
    Summary: Apply tactics: Consider whether to launch a missile at us
  Deep dive: Program flow of the tactics routine

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: No direct references to this subroutine in this source file




 This section considers whether to launch a missile. Specifically:

   * If the ship doesn't have any missiles, skip to the next part

   * If an E.C.M. is firing, skip to the next part

   * Randomly decide whether to fire a missile, and if we do, we're done



.ta3

                        \ If we get here then the ship has less than half energy
                        \ so there may not be enough juice for lasers, but let's
                        \ see if we can fire a missile

 LDA INWK+31            \ Set A = bits 0-2 of byte #31, the number of missiles
 AND #%00000111         \ the ship has left

 BEQ TA3                \ If it doesn't have any missiles, jump to TA3

 STA T                  \ Store the number of missiles in T

 JSR DORND              \ Set A and X to random numbers

 AND #31                \ Restrict A to a random number in the range 0-31

 CMP T                  \ If A >= T, which is quite likely, though less likely
 BCS TA3                \ with higher numbers of missiles, jump to TA3 to skip
                        \ firing a missile

 LDA ECMA               \ If an E.C.M. is currently active (either ours or an
 BNE TA3                \ opponent's), jump to TA3 to skip firing a missile

 DEC INWK+31            \ We're done with the checks, so it's time to fire off a
                        \ missile, so reduce the missile count in byte #31 by 1

 LDA TYPE               \ Fetch the ship type into A

.TA16

 JMP SFRMIS             \ Jump to SFRMIS to spawn a missile as a child of the
                        \ current ship, make a noise and print a message warning
                        \ of incoming missiles, and return from the subroutine
                        \ using a tail call