6502 xorshift, 8-bit full period

gistfile1.txt

; r ^= (r << 1)
; r ^= (r >> 1)
; r ^= (r << 2)

xorshift:
        lda <RAND_SEED
        asl a
        eor <RAND_SEED
        tax
        asr a
        eor x
        tax
        asr a
        asr a
        eor x
        rts

16 bit version:
(It may be incorrect...)

Random:
  lda random + 1
  pha
  lda random
  asl a
  rol random + 1
  asl a
  rol random + 1
  asl a
  rol random + 1
  asl a
  rol random + 1
  asl a
  rol random + 1
  asl a
  rol random + 1
  asl a
  rol random + 1
  eor random
  sta random
  pla
  eor random + 1
  sta random + 1
  lsr a
  eor random
  sta random
  eor random + 1
  sta random + 1
  rts

http://www.retroprogramming.com/2017/07/xorshift-pseudorandom-numbers-in-z80.html