Nightshade: Routine at C5B4

Used by the routines at NEW_GAME, STOCK_BUILDINGS, MENU, PLACE_OBJECTS and PLACE_VILLAINS.

NEXT_TURN adds one to TURNS, once a turn in the main loop and at a few points of a new game's set-up. STIR_RANDOM, the rest, is called after every record's update and before most random choices. The random number's low byte becomes R plus itself plus the turn counter's low byte, with the carry; its high byte just adds the turn counter's high byte, with no carry from the low. R counts the instructions run, which depends on all the game has done, so the low byte is hard to predict; the high byte is not -- a fixed step, the same for 256 turns at a time, added once a stir.

Used by the routines at NEW_GAME, STOCK_BUILDINGS, MENU, PLACE_OBJECTS and PLACE_VILLAINS. NEXT_TURN adds one to TURNS, once a turn in the main loop and at a few points of a new game's set-up. STIR_RANDOM, the rest, is called after every record's update and before most random choices. The random number's low byte becomes R plus itself plus the turn counter's low byte, with the carry; its high byte just adds the turn counter's high byte, with no carry from the low. R counts the instructions run, which depends on all the game has done, so the low byte is hard to predict; the high byte is not -- a fixed step, the same for 256 turns at a time, added once a stir.
NEXT_TURN	C5B4	LD HL,(TURNS)	one more turn
	C5B7	INC HL
	C5B8	LD (TURNS),HL
This entry point is used by the routines at NEW_GAME, RANDOM_START_CELL, SPAWN_MONSTER and PLACE_BONUS.
STIR_RANDOM	C5BB	LD HL,(TURNS)	STIR_RANDOM: the low byte from R, itself and the counter's low byte; the high byte plus the counter's high byte
	C5BE	LD DE,(RANDOM)
	C5C2	LD A,R
	C5C4	ADD A,E
	C5C5	ADC A,L
	C5C6	LD L,A
	C5C7	LD A,D
	C5C8	ADD A,H
	C5C9	LD H,A
	C5CA	LD (RANDOM),HL	kept
	C5CD	RET	kept