Routines
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41325: Multiply Words
Used by the routine at GetRoomPointer.
Multiplies the word in HL by the word in DE. GetRoomPointer uses it to multiply the current room number by 6 to find that room's record in Table_RoomMap.
Input
HL Multiplicand
DE Multiplier
Output
HL Product
MultiplyWords 41325 PUSH BC Stash BC on the stack.
41326 LD B,16 B=16.
41328 LD A,H A=H.
41329 LD C,L C=L.
41330 LD HL,0 HL=0000.
MultiplyWords_0 41333 ADD HL,HL HL+=HL.
For each bit of the multiplier, shift it into the carry and add the multiplicand when that bit is set.
41334 AND A Fold the next multiplier bit into the product.
41335 RL C
41337 RLA
41338 JR NC,MultiplyWords_1
41340 ADD HL,DE
MultiplyWords_1 41341 DJNZ MultiplyWords_0
41343 POP BC Restore BC from the stack, leaving the product in HL.
41344 RET Return.
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