How did Mega-Lo-Mania's save state system work?

Question

To continue a game in Mega-Lo-Mania (AKA Tyrants) on the Sega Megadrive/Genesis, you would enter an eight digit code into the interface and then you could resume a session.

Presumably, the code contains information about the state of the game since neither the Megadrive nor the cartridge had no means to persist data for the game between power cycles. I also suspect that the code includes a sort of parity check to prevent random codes from being used.

What is the breakdown of the Mega-Lo-Mania code data format, and how can a custom save state be generated to target a particular world and set of circumstances?

Answer 1

The password is made of 11 capital letters (A to Z) and encodes the following values:

• A value from 0 to 3 that indicates the selected player (red, green, yellow, or blue).

• A value from 0 to 9 that indicates the starting epoch (1st to 9th epoch or Megalomania).

• The number of men, from 0 to 999.

• Four unknown values, each from 0 to 49. (I haven't played the game to confirm where these values are used, but a hypothesis is that some of these values may be related to the number of men you put into suspended animation in the 7th, 8th, and 9th epochs. In the password lists below, the unknown values are zero until the passwords for starting on the 8th epoch.)

The encoding process includes the following kinds of steps:

• The last character of the password is a checksum generated with addition and exclusive or operations.

• The bits of data are obfuscated with bit rotation and exclusive or operations.

• Some of the unused bits that would have normally been zero are instead filled with amounts based on counting the number of "1" bits in segments of the data.

I created a simple Mega-Lo-Mania Password Generator in HTML and JavaScript. Here are some JavaScript snippets adapted from it that show the encoding process:

player = 0;
epoch = 0;
men = 100;
w = 0;  // unknown values
x = 0;
y = 0;
z = 0;

d0 = 40 * men + 4 * epoch + player;
d1 = 50 * w + x;
d2 = 50 * y + z;

k = d0;  // checksum
k ^= 0x2435;
k += d1;
k ^= 0x2435;
k += d2;
k ^= 0x2435;
k &= 0xFFFF;
k %= 26;

d1 = (d0 & 0xFFF) ^ d1;
d2 = ( (d0 >> 3) & 0xFFF ) ^ d2;
d0 = ( ((d0 & 0xF800) >> 11) | ((d0 & 0x07FF) << 5) ) ^ 0x2435;

d1 = ((count_bits(d1) & 3) << 12) | d1;
d2 = ((count_bits(d2) & 3) << 12) | d2;

password = "";
password += base26(d0, 4);  // 4 letters, A to Z, little-endian
password += base26(d1, 3);  // 3 letters
password += base26(d2, 3);  // 3 letters
password += base26(k,  1);  // 1 letter

Here are some example passwords and the data they contain.

From IGN Genesis Cheats - MEGAloMANIA: Jikuu Daisenryaku:

Password	Player	Epoch	Men	Unknown
NZUCWTIAEHV	Red	2nd	148	0 0 0 0
ARTCKXKNMND	Red	3rd	184	0 0 0 0
YLGBUMQZKNL	Red	4th	176	0 0 0 0
IHUBUGQULTB	Red	5th	172	0 0 0 0
COCAKLDWEBX	Red	6th	160	0 0 0 0
EBWROLJUHNJ *
EBWAOLJUHNJ **	Red	7th	159	0 0 0 0
QPIAXODAHHM	Red	8th	163	5 1 0 0
ZBLDRNIHGTY	Red	9th	143	5 1 0 0
CPFDVMRBYST	Red	Megalomania	100	10 1 0 1

* sic, invalid password
** corrected

From GameFAQs Tyrants: Fight Through Time (Genesis) - Cheats:

Password	Player	Epoch	Men	Unknown
SIZCSVLOPNL	Red	1st	200	0 0 0 0
SMLCUQKDKHH	Red	2nd	999	0 0 0 0
WQICAUWQIBN	Red	3rd	999	0 0 0 0
UVICOPEQIBJ	Red	4th	999	0 0 0 0
SAJCSPEFKHV	Red	5th	999	0 0 0 0
QFJCKRKFKHR	Red	6th	999	0 0 0 0
OKJCAQEGKHX	Red	7th	999	0 0 0 0
MPJCDWEGKHK	Red	8th	999	5 1 0 0
KUJCTYQVLNW	Red	9th	999	5 1 0 0
IZJCJKXGKHD	Red	Megalomania	999	10 1 0 1