Randomness

The randomness is at 0x7E0408 and is 16 bytes. It is set to all zero on reset of the game.

Randomness Advancements

• Ark idle animation
• Ark gets hit
• Enemy gets hit
• Enemy logic calls the random function
• NPC randomly walks around
• Sprite animations

Manipulations

Since on reset the randomness has a known starting point and a predicable continuation of the values, it is possible in certain cases to manipulate it.

• Ghost fight
• Dragoon Castle guard pattern
• Dark Gaia
• Quintet Quiz

Code

Note: This is simply translated from the assembler code

typedef unsigned char u8;
typedef unsigned char u16;

u8 seed[16];

void random( u8 *seed )
{
	u8 x = 0xF;
	u8 a = 0;
	u8 b = 0;
	u8 c = 0;

loc_C68242:
	a = seed[x];

	u8 r = 0;

	if( a + c + seed[x-1] > 0xFF )
		r = 1;
	else
		r = 0;

	a += c + seed[x-1];

	c = r;

	seed[x-1] = a;
	x = x - 1;
	if( x > 0 )
		goto loc_C68242;

	x = 0x10;

loc_C68251: 
	if( seed[x-1] + 1 > 0xFF )
		r = 1;
	else
		r = 0;

	seed[x-1] += 1;
	if(r==0)
		goto loc_C68259;

	x = x - 1;
	if( x > 0 )
		goto loc_C68251;

loc_C68259:
;
}

example implementation in python3

#!/usr/bin/env python3
state = [0] * 16

def rng():
    carry = 0
    for i in range(15,0,-1):
        carry, state[i-1] = divmod(carry + state[i-1] + state[i], 256)

    for i in range(15,-1,-1):
        state[i] = (state[i] + 1) % 256
        if state[i] != 0:
            break
    return state[0]

for _ in range(20):
    print(hex(rng()))