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Elite on the BBC Micro

Version analysis of TACTICS (Part 5 of 7)

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

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

Code variation 1 of 2A variation in the comments only

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, 6502SP, Master


* Randomly decide whether to fire a missile (or, in the case of Thargoids, release a Thargon), and if we do, we're done
* 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 our's 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

Code variation 2 of 2Related to the Electron version

The Electron version has no Thargoids, which also means no ships can launch Thargons.

This variation is blank in the Electron version.

Cassette, Flight, 6502SP, Master

CMP #THG \ If this is not a Thargoid, jump down to TA16 to launch BNE TA16 \ a missile LDX #TGL \ This is a Thargoid, so instead of launching a missile, LDA INWK+32 \ the mothership launches a Thargon, so call SFS1 to JMP SFS1 \ spawn a Thargon from the parent ship, and return from \ the subroutine using a tail call

 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

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