Routines
Prev: 4000 Up: Map Next: 48A1
4885: Decrypt Game
After the tape load, the game is still encoded. This stub sits in the loading-screen bitmap, restores the 7F94 bytes below FFFE then starts the title/menu at Initialise_Game.
Decrypt_Game 4885 XOR A Use the whole screen; no rows are reserved for BASIC.
4886 LD ($5C6B),A
4889 LD DE,$FFFE Point at the last encoded byte and set the length to 7F94.
488C LD HL,$FFFD
488F LD BC,$7F94
Undo the tape encoding: complement, subtract one, and store the byte one address higher. Walks backwards through the loaded game until every encoded byte is restored.
Decrypt_Game_Loop 4892 LD A,(HL) Decode one byte and step both pointers down.
4893 CPL
4894 DEC A
4895 LD (DE),A
4896 DEC DE
4897 DEC HL
4898 DEC BC
4899 LD A,B Jump to Decrypt_Game_Loop until the whole image is restored.
489A OR C
489B JP NZ,Decrypt_Game_Loop
489E JP Initialise_Game Jump to Initialise_Game.
Prev: 4000 Up: Map Next: 48A1