Routines
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39090: Find World Map Address
Used by the routines at Read_World_Map, Handle_Sabreman_Falling, Lower_Rope and Raise_Rope.
Works out the address in the World_Map world map of the entry for the room that the object at IX is in. The address is 28672 plus 32 times the room y plus twice the room x.
The multiplication of the room y by 32 is done as a multiplication of the low three bits of the room y by 32 plus 256 times the rest of the room y.
Input
IX Object record
Output
HL Address of the world map entry
Find_World_Map_Address 39090 PUSH BC Stash BC on the stack.
39091 LD H,(IX+4) Fetch the room y of the object into H.
39094 XOR A Start the offset at zero.
39095 SRL H Move bit 0 of the room y into A.
39097 RRA
39098 SRL H Move bit 1 of the room y into A.
39100 RRA
39101 SRL H Move bit 2 of the room y into A. (A is now 32 times the low three bits.)
39103 RRA
39104 LD L,(IX+2) Fetch the room x of the object into L.
39107 ADD A,L Add the room x to A.
39108 ADD A,L Add the room x to A again, to make twice the room x.
39109 LD L,A Store the low byte of the offset in L.
39110 LD BC,28672 Point at the world map (World_Map).
39113 ADD HL,BC Add the address of the world map to the offset.
39114 POP BC Restore BC from the stack.
39115 RET Return.
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