MSX Village forum

 
 
;This is a very simple linear congruential generator. 
;The formula is x[i + 1] = (5 * x[i] + 1) mod 256. 
;Its only advantage is small size and simplicity. 
;Due to nature of such generators only a couple of higher bits should be considered random.
 
;Input: none
;Output: A = pseudo-random number, period 256
 
Rand8lda,Seed; Seed is usually 0
ldb,a
adda,a
adda,a
adda,b
inca; another possibility is ADD A,7
ld(Rand8+1),a
ret
 

 
 
;This generator is based on similar method but gives much better results. 
;It was taken from an old ZX Spectrum game and slightly optimised.
 
;Input: none
;Output: HL = pseudo-random number, period 65536
 
Rand16ldde,Seed; Seed is usually 0
lda,d
ldh,e
ldl,253
ora
sbchl,de
sbca,0
sbchl,de
ldd,0
sbca,d
lde,a
sbchl,de
jrnc,Rand
inchl
Randld(Rand16+1),hl
ret