mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-04 20:06:09 +00:00
120 lines
2.5 KiB
ArmAsm
120 lines
2.5 KiB
ArmAsm
|
; 16-bit 6502 Random Number Generator (cycle-invariant version)
|
||
|
|
|
||
|
|
; Linear feedback shift register PRNG by White Flame
|
||
|
|
; http://codebase64.org/doku.php?id=base:small_fast_16-bit_prng
|
||
|
|
|
||
|
|
; The Apple II KEYIN routine increments SEEDL:SEEDH
|
||
|
|
; while waiting for keypress
|
||
|
|
|
||
|
|
SEEDL = $4E
|
||
|
|
SEEDH = $4F
|
||
|
|
|
||
|
|
XOR_MAGIC = $7657 ; "vW"
|
||
|
|
|
||
|
|
;=============================
|
||
|
|
; random16
|
||
|
|
;=============================
|
||
|
|
; takes:
|
||
|
|
; not 0, cs = 6(r16)+12(lnz)+5(nop)+ 19(deo) = 42
|
||
|
|
; not 0, cc = 6(r16)+14(lnz)+2(nop)+ 20(neo) = 42
|
||
|
|
|
||
|
|
; $0000 = 6(r16)+ 6(loz)+11nops+ 19(deo) = 42
|
||
|
|
; $8000 = 6(r16)+ 6(loz)+ 4(ceo) + 6nops+ 20(neo) = 42
|
||
|
|
|
||
|
|
; $XX00 cc = 6(r16)+ 6(loz)+4(ceo)+2(cep) +4nops+ 20(neo) = 42
|
||
|
|
; $XX00 cs = 6(r16)+ 6(loz)+4(ceo)+4(cep) +3nops+ 19(deo) = 42*
|
||
|
|
random16:
|
||
|
|
|
||
|
|
lda SEEDL ; 3
|
||
|
|
beq low_zero ; $0000 and $8000 are special values ; 3
|
||
|
|
;==========
|
||
|
|
; 6
|
||
|
|
lownz:
|
||
|
|
; -1
|
||
|
|
asl SEEDL ; Do a normal shift ; 5
|
||
|
|
lda SEEDH ; 3
|
||
|
|
rol ; 2
|
||
|
|
bcs five_cycle_do_eor ; 3
|
||
|
|
;===========
|
||
|
|
; 12
|
||
|
|
|
||
|
|
bcc two_cycle_no_eor ; 3
|
||
|
|
;==========
|
||
|
|
; 12+3-1 = 14
|
||
|
|
|
||
|
|
|
||
|
|
;===================================================================
|
||
|
|
|
||
|
|
eleven_cycle_do_eor:
|
||
|
|
nop ; 2
|
||
|
|
nop ; 2
|
||
|
|
nop ; 2
|
||
|
|
five_cycle_do_eor:
|
||
|
|
nop ; 2
|
||
|
|
three_cycle_do_eor:
|
||
|
|
sta SEEDH ; nop ; 3
|
||
|
|
|
||
|
|
do_eor:
|
||
|
|
; high byte is in A
|
||
|
|
|
||
|
|
eor #>XOR_MAGIC ; 2
|
||
|
|
sta SEEDH ; 3
|
||
|
|
lda SEEDL ; 3
|
||
|
|
eor #<XOR_MAGIC ; 2
|
||
|
|
sta SEEDL ; 3
|
||
|
|
eor_rts:
|
||
|
|
rts ; 6
|
||
|
|
;===========
|
||
|
|
; 19
|
||
|
|
|
||
|
|
;=========================================================================
|
||
|
|
|
||
|
|
six_cycles_no_eor:
|
||
|
|
nop ; 2
|
||
|
|
four_cycle_no_eor:
|
||
|
|
nop ; 2
|
||
|
|
two_cycle_no_eor:
|
||
|
|
nop ; 2
|
||
|
|
no_eor:
|
||
|
|
nop ; 2
|
||
|
|
nop ; 2
|
||
|
|
nop ; 2
|
||
|
|
nop ; 2
|
||
|
|
sta SEEDH ; 3
|
||
|
|
jmp eor_rts ; 3+6
|
||
|
|
;===========
|
||
|
|
; 20
|
||
|
|
|
||
|
|
|
||
|
|
;======================================================================
|
||
|
|
;======================================================================
|
||
|
|
|
||
|
|
low_zero:
|
||
|
|
lda SEEDH ; 3
|
||
|
|
beq eleven_cycle_do_eor ; High byte is also zero ; 3
|
||
|
|
; so apply the EOR
|
||
|
|
;============
|
||
|
|
; 6
|
||
|
|
ceo:
|
||
|
|
|
||
|
|
; -1
|
||
|
|
; wasn't zero, check for $8000
|
||
|
|
asl ; 2
|
||
|
|
beq six_cycles_no_eor ; if $00 is left after the shift; 3
|
||
|
|
; then it was $80
|
||
|
|
;===========
|
||
|
|
; 4
|
||
|
|
|
||
|
|
; else, do the EOR based on the carry
|
||
|
|
cep:
|
||
|
|
; -1
|
||
|
|
bcc four_cycle_no_eor ; 3
|
||
|
|
;============
|
||
|
|
; 2
|
||
|
|
|
||
|
|
bcs three_cycle_do_eor ; 2+3-1 = 4
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|