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Version analysis of DEEOR

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

Code variations between these versions are shown below.

Name: DEEOR Type: Subroutine Category: Loader

Code variation 1 of 3A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Summary: Decrypt the main docked code between &1300 and &5FFF and the main game loop
Summary: Decrypt the main flight code between &1300 and &55FF and jump into the main game loop
.DEEOR IF _STH_DISC OR _IB_DISC LDY #0 \ We're going to work our way through a large number of \ encrypted bytes, so we set Y to 0 to be the index of \ the current byte within its page in memory STY SC \ Set the low byte of SC(1 0) to 0 LDX #&13 \ Set X to &13 to be the page number of the current \ byte, so we start the decryption with the first byte \ of page &13 .DEEORL STX SCH \ Set the high byte of SC(1 0) to X, so SC(1 0) now \ points to the first byte of page X TYA \ Set A to Y, so A now contains the index of the current \ byte within its page EOR (SC),Y \ EOR the current byte with its index within the page EOR #&33 \ EOR the current byte with &33 STA (SC),Y \ Update the current byte \ The current byte is in page X at offset Y, and SC(1 0) \ points to the first byte of page X, so we just did \ this: \ \ (X Y) = (X Y) EOR Y EOR &33 DEY \ Decrement the index in Y to point to the next byte BNE DEEORL \ Loop back to DEEORL to decrypt the next byte until we \ have done the whole page INX \ Increment X to point to the next page in memory

Code variation 2 of 3Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

CPX #&60 \ Loop back to DEEORL to decrypt the next page until we BNE DEEORL \ reach the start of page &60 JMP BRKBK \ Call BRKBK to set BRKV to point to the BRBR routine \ and return from the subroutine using a tail call
CPX #&56 \ Loop back to DEEORL to decrypt the next page until we BNE DEEORL \ reach the start of page &56 JMP RSHIPS \ Call RSHIPS to launch from the station, load a new set \ of ship blueprints and jump into the main game loop
ELIF _SRAM_DISC

Code variation 3 of 3Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

NOP \ The sideways RAM variant is not encrypted, so the NOP \ decryption code is disabled and is replaced by NOPs NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP NOP JMP BRKBK \ Call BRKBK to set BRKV to point to the BRBR routine \ and return from the subroutine using a tail call
JMP RSHIPS \ Call RSHIPS to launch from the station, load a new set \ of ship blueprints and jump into the main game loop
ENDIF