Platinum - 0x0201D30C routine (Great Marsh) study
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ARM7 code :

0201:D30C	LDR		R1, [PC, #4]	| Load the value PC+4 into R1
0201:D30E	MUL		R1, R0			| R1 = R1*R0
0201:D310	ADD		R0, R1, #1		| R0 = R1 + 1
0201:D312	BX		LR				| Branch to adress in LR and LR[0] indicates the operating mode (ARM or Thumb)
0201:D314	LDRH	R5, [R4, #A]	| Load register from memory (halfword)
0201:D316	LDR		R7, [R0, #40]	| Load register from memory
0201:D318	PUSH	{R4-R5}			| Push in stack
0201:D31A	LDR		R1, [PC, #30]	| Load register from memory
0201:D31C	MOV		R4, #27			| Move register or constant
0201:D31E	STR		R0, [R1, #8]	| Store register to memory
0201:D320	LDR		R1, [PC, #2C]	| Load register from memory
0201:D322	MOV		R0, #1			| Move register or constant
0201:D324	STR		R0, [R1, #0]	| Store register to memory
0201:D326	LDR		R1, [PC, #2C]	| Load register from memory
0201:D328	LDR		R3, [PC, #2C]	| Load register from memory
0201:D32A	LSL		R4, R4, #4		| Logical shift left
0201:D32C	SUB		R2, R1, #4		| Subtract
0201:D32E	LDR		R5, [R2, #0]	| Load register from memory
0201:D330	LSR		R2, R5, #1E		| Logical shift right
0201:D332	EOR		R2, R5			| Exclusive OR
0201:D334	ADD		R5, R2, #0		| Add
0201:D336	MUL		R5, R3			| Multiply
0201:D338	ADD		R2, R0, R5		| Add
0201:D33A	ADD		R0, R0, #1		| Add
0201:D33C	STMIA	R1!, {R2}		| Store multiple, increment after
0201:D33E	CMP		R0, R4			| Compare
0201:D340	BLT		#0201D32C		| Branch lower than
0201:D342	LDR		R1, [PC, #C]	| Load register from memory
0201:D344	STR		R0, [R1, #0]	| Store register to memory
0201:D346	POP		{R4-R5}			| Pop from stack
0201:D348	BX		LR

Registers (before) :
R0  = 00000E0B	R4  = 00000000	R8  = 0000FFFF	R12 = 038008CF
R1  = 03806BF0	R5  = 00000070	R9  = 00000002	SP  = 0380F944
R2  = 027FFC3C	R6  = 00000002	R10 = 00000000	LR  = 037F8434
R3  = 04000004	R7  = 0380F954	R11 = 00000000	PC  = 037F8484


Registers (after) :
R0  = 00000E0C	R4  = 00000000	R8  = 0000FFFF	R12 = 038008CF
R1  = 03806BF0	R5  = 00000070	R9  = 00000002	SP  = 0380F944
R2  = 027FFC3C	R6  = 00000002	R10 = 00000000	LR  = 037F8434
R3  = 04000004	R7  = 0380F954	R11 = 00000000	PC  = 037F8484