FE12 Growth Rate Cipher Documentation

[SciresM]

Hi there. 

A few weeks back, I documented the growth rate cipher for Fire Emblem Awakening. Apparently, FE12's growth rate cipher was also undocumented. Let's fix that :)

As an example, I will be using Marth's growth rates.

Note: Much of this is copy/pasted from my awakening growth document, but this was documented by loading FE12 in No$GBA's debugger.

 

Also note: decrypt_class_growth(classdata_ptr, enciphered_growth_rate, growth_rate_index) is at 0x2049418 when FE12 is in RAM. decrypt_unit_growth(unitdata_ptr, enciphered_growth_rate, growth_rate_index) is at 0x2049280 when FE12 is in RAM. 

 

Unit Growth Rates

Growth rate data is stored, enciphered, as a sequence of 8 bytes, in the usual stat ordering (HP, Str, Mag, Skl, Spd, Lck, Def, Res).

Marth's growth rates for example, are the highly inscrutable `D1 E3 6C E1 F6 2E 15 49 98`.

 

The conversion process is both simple, and fairly complex. To lookup the growth rate for the stat at index N (zero-indexing), we perform the calculation

INDEX = (ENCIPHERED[N]- (0x57 * ((CHARACTER_ID ^ 0x3E) - 3 * N) ^ 0xF5)) & 0xFF;

GROWTH_RATE = LOOKUP_TABLE[INDEX];

Where LOOKUP_TABLE is the following lookup table, found at 0xF408 in FE12Data.bin:

3C 7F 83 81 80 78 6A 08 BC D8 75 89 2C 41 BD C6 4A C7 AE A0 19 72 28 03 40 99 43 42 07 A5 74 B4 DB D0 50 18 A4 F9 91 88 CB 5F 55 DD 82 3A 93 0A D4 26 1A D1 29 85 AB EF 5A 12 B0 EA 7C 6B 4F 9D 06 27 E2 64 4C E4 BB EE 6F 8B 2F 30 51 61 65 A7 77 FA 5D E1 CE FD 5C F8 8F 8C C3 A1 CA DE CF F5 B2 69 D5 B5 23 C8 0B 31 3F 60 20 C2 3B AF 1C 05 92 6D 8E 71 36 96 22 2B 1B 3D FF 73 59 BE 35 BA B1 45 15 CC 4B 1D 7A 9C 0E 84 49 67 AD F0 0F 2E 5E 16 7B F7 52 BF EB 9B C5 E3 DC 02 8D 04 F6 21 C0 38 3E 4D 11 E9 1F FB A6 AC 94 62 2A D9 A8 C4 F3 00 C1 CD D3 9F A3 9E EC D7 FC E8 0D 47 48 90 E5 58 DA A9 56 FE D6 34 6E AA 0C 8A 95 17 01 68 09 B7 E7 37 25 79 E6 63 98 B9 33 B6 87 86 24 A2 70 76 5B F2 44 13 E0 46 53 B8 32 2D 10 1E C9 7D 14 F1 9A D2 57 4E F4 ED 97 B3 DF 39 54 66 6C 7E

Okay, there's basically no chance that was clear. So let's do the calculations, to make it a bit clearer.

Suppose we want the HP growth rate. That's stat 0. Enciphered[0] is 0xD1, and Marth's character ID is 0, so we calculate INDEX = (0xD1 - (0x57 * ((0 ^ 0x3E) - 3 * 0) ^ 0xF5)) & 0xFF = 0xEA. The value in the lookup table at index 0xEA is 0x32, or 50 -- Marth's base HP growth rate.

Suppose we want the Lck growth rate. That's stat 5. Enciphered[5] is 0x2E, and Marth's character ID is 0, so we calculate INDEX = (0x2E - (0x57 * ((0 ^ 0x3E) - 3 * 5) ^ 0xF5)) & 0xFF = 0x22. The value in the lookup table at index 0x22 is 0x50, or 80 -- Marth's base Lck growth rate.

 

Class Growth Rates

As with unit growth rate data, class growth rate data is stored, again enciphered as a sequence of 8 bytes in the usual ordering.

Marth's base class is Lord, which has enciphered growth rate `32 C7 C4 B3 D8 46 21 06`.

 

The conversion process for class growth rates proceeds much like the unit growth rate -- the formula is just different. We perform the calculation:

INDEX = (ENCIPHERED[N]- (0xB3 * ((CLASS_ID ^ 0x9D) - 7 * N) ^ 0xDB)) & 0xFF;

GROWTH_RATE = LOOKUP_TABLE[INDEX];

Where LOOKUP_TABLE is the same as it was for unit growth rates.

 

Again, walking through the calculations for Lord:

Suppose we want the HP growth rate. That's stat 0. Enciphered[0] is 0x32, and Lord's class ID is 0, so we calculate INDEX = (0x32 - (0xB3 * ((0 ^ 0x9D) - 7 * 0) ^ 0xDB)) & 0xFF = 0x16. The value in the lookup table at index 0x16 is 0x28, or 40 -- Lord's base HP growth rate.

Suppose we want the Lck growth rate. That's stat 5. Enciphered[5] is 0x46, and Lord's class ID is 0, so we calculate INDEX = (0x46 - (0xB3 * ((0 ^ 0x9D) - 7 * 5) ^ 0xDB)) & 0xFF = 0xB1. The value in the lookup table at index 0xB1 is 0x00, or 0 -- Lord's base Lck growth rate.

 

Hope this is clear, feel free to ask any clarifying questions, and have fun playing around with growth rates!

Edited April 9, 2017 by SciresM