Here is a bit shorter version:

;Rnew = Rold * 221 + 53
;221 = 256 - 32 - 4 + 1
;256 can be eliminated
;so we need to calculate Rnew = Rold * (1 - 32 - 4) + 53 using
;truncating arithmetic
;or Rnew = Rold * (-32 - 3) + 53

        clrc
        rlf RANDOM, f
        swapf RANDOM, w
        andlw 0xE0
        rrf RANDOM, f
        addwf RANDOM, w
        addwf RANDOM, w
        addwf RANDOM, w
        sublw 0x35
        movwf RANDOM

Does anybody know how to estimate randomness of a pseudo-random
generator? Or what other methods are out there?

 Nikolai
 http://techref.massmind.org/member/NG--944