pseudorandom number on i8080

based on two different articles from the internet Smile

Code:

;=======================================================================
;   RND -> DEHL
;-----------------------------------------------------------------------
get_rnd:
    lda .cnt
    dcr a
    jnz .lfsr
    lhld rnd
    lxi b,64525
    call umul
    push h
    push d
    lhld rnd+2
    call umul
    pop b
    dad h
    xchg
    pop h
    lxi b,1013904223 shr 16
    xchg
    dad b
    xchg
    lxi b,1013904223 and 0FFFFh
    dad b
    jnc @F
    inx d
@@:
    shld rnd
    xchg
    shld rnd+2
    mvi a,31
;-----------------------------------------------------------------------
.lfsr:
    sta .cnt
    lhld rnd+2
    xchg
    lhld rnd
    mov a,l
    xri 57h
    mov l,a
    mov a,d
    xri 80h
    mov d,a
    xchg
    dad h
    xchg
    dad h
    jnc @F
    inx d
@@:
    ral
    jnc @F
    inx h
@@:
    shld rnd
    xchg
    shld rnd+2
    xchg
    ret
;-----------------------------------------------------------------------
.cnt:   db 31
;=======================================================================
;
;=======================================================================
rnd:    dd 1
;=======================================================================

needs multiplication:

Code:

;=======================================================================
;   DEHL = HL * BC
;-----------------------------------------------------------------------
umul:  
    lxi  d,0
    mvi  a,16
umx1: 
    dad  h
    xchg
    jnc  umx3
    dad  h
    jnc  umx2
    inx  d
umx2: 
    dad  b
    jnc  umx4
    inx  d
    jmp  umx4
umx3: 
    dad  h
    jnc  umx4
    inx  d
umx4: 
    xchg
    dcr  a
    jnz  umx1
    xchg
    ret
;=======================================================================

tested with this way:

Code:

;-----------------------------------------------------------------------
    call 0C010h
;-----------------------------------------------------------------------
    lxi h,30101
    lxi d,10103
    call set_rnd
@@:
    call get_rnd
    xra a
    mov h,a
    inr a
    ana d
    mov d,a
    mvi a,-1
    call put_pixel
    lda 0FF01h ; exit if shift pressed
    rar
    rar
    jc  @B
;-----------------------------------------------------------------------
    ret    
;-----------------------------------------------------------------------

not ideal, you may see the result here, but maybe enough for common case Smile