Unmangling and decoding algorithms

File unmangling

"RLE algorithm on steroids" adapted from this implementation by @samunders-core. Files are mangled in the release versions of Fatal Racing and Whiplash but not in the Fatal Racing demo or beta.

Original unmangler

The Actua Soccer/UEFA Euro 96 England source code was accidentally distributed on the cover disc of issue 71 (May 1996) of French computer magazine Joystick, including the original unmangler implementation (UNMANGLE.C). The source code was later made available on the Gremlin Archive under a CC BY-NC-ND 4.0 licence.

Note that UNMANGLE.C ignores the 4-byte header containing the unmangled file length and instead terminates the output when a zero control byte is found. However, the header is used by SOUND.C in Fatal Racing/Whiplash (loadfile and getcompactedfilelength).

File decoding

Encoding is applied to .KC files (cheat audio activated by TOPTUNES), FATAL.INI (configuration file) and PASSWORD.INI (cheat names). To decode these, apply a bitwise XOR against the Fibonacci-like sequence $a_n = a_{n-1} + a_{n-2}$ with the first byte XORed against $a_2$, defined by the following initial constants:

• .KC files: $a_0 = 115$, $a_1 = 150$

  Note .KC files must be unmangled first, then decoded.

• FATAL.INI: $a_0 = 77$, $a_1 = 101$

• PASSWORD.INI: $a_0 = 23$, $a_1 = 37$

  By decoding PASSWORD.INI in Fatal Racing V2.0 builds or Whiplash we can find two undocumented cheat names:

  • PROCESS: performs a Pentium FDIV bug check and changes to TYPE A if the bug is found or TYPE B if not
  • CLONES: not implemented.

frontend.c also calls this function with $a_0 = 43$ and $a_1 = 87$ to decode/re-encode the list of cheat names.