( https://codebase64.org/doku.php?id=base:16bit_xorshift_random_generator )
1 var, prngstate
:asm rand
  MOV AX prngstate @+
  MOV BX AX
  RCR BX 1 #
  XOR AH BL  ( high part of x ^= x << 7 )
  MOV BH AH
  RCR BH 1 # ( BH now has x >> 9 and high bit comes from low byte )
  XOR AL BH ( x ^= x >> 9 and the low part of x ^= x << 7 done )
  XOR AH AL ( x ^= x << 8 )
  MOV prngstate @+ AX
  PUSH AX
  NEXT

:asm ticks
  XOR AX AX
  INT 0x1a #
  PUSH DX
  NEXT

: reseed! ticks prngstate ! ;