.include "../platform/c64_0.oph"
.require "../platform/c64kernal.oph"
.outfile "fibonacci.prg"
lda #<opening ; Print opening text
sta fun'args
lda #>opening
sta fun'args+1
jsr print'string
lda #$00
sta fun'vars ; Count num from 0 to 19
* lda fun'vars ; Main loop: print num, with leading space if <10
cmp #$09
bcs +
lda #$20
jsr chrout
lda fun'vars
* sta fun'args ; Copy num to args, print it, plus ": "
inc fun'args
lda #$00
sta fun'args+1
jsr print'dec
lda #$3A
jsr chrout
lda #$20
jsr chrout
lda fun'vars ; Copy num to args, call fib, print result
sta fun'args
jsr fib
jsr print'dec
lda #$0D ; Newline
jsr chrout
inc fun'vars ; Increment num; if it's 20, we're done.
lda fun'vars
cmp #20
bne -- ; Otherwise, loop.
rts
opening:
.byte 147, " FIBONACCI SEQUENCE",13,13,0
.scope
; Uint16 fib (Uint8 x): compute Xth fibonnaci number.
; fib(0) = fib(1) = 1.
; Stack usage: 3.
fib: lda #$03
jsr save'stack
lda fun'vars ; If x < 2, goto _base.
cmp #$02
bcc _base
dec fun'args ; Otherwise, call fib(x-1)...
jsr fib
lda fun'args ; Copy the result to local variable...
sta fun'vars+1
lda fun'args+1
sta fun'vars+2
lda fun'vars ; Call fib(x-2)...
sec
sbc #$02
sta fun'args
jsr fib
clc ; And add the old result to it, leaving it
lda fun'args ; in the 'result' location.
adc fun'vars+1
sta fun'args
lda fun'args+1
adc fun'vars+2
sta fun'args+1
jmp _done ; and then we're done.
_base: ldy #$01 ; In the base case, just copy 1 to the
sty fun'args ; result.
dey
sty fun'args+1
_done: lda #$03
jsr restore'stack
rts
.scend
.scope
; Stack routines: init'stack, save'stack, restore'stack
.data zp
.space _sp $02
.space _counter $01
.space fun'args $10
.space fun'vars $40
.text
init'stack:
lda #$00
sta _sp
lda #$A0
sta _sp+1
rts
save'stack:
sta _counter
sec
lda _sp
sbc _counter
sta _sp
lda _sp+1
sbc #$00
sta _sp+1
ldy #$00
* lda fun'vars, y
sta (_sp), y
lda fun'args, y
sta fun'vars, y
iny
dec _counter
bne -
rts
restore'stack:
pha
sta _counter
ldy #$00
* lda (_sp), y
sta fun'vars, y
iny
dec _counter
bne -
pla
clc
adc _sp
sta _sp
lda _sp+1
adc #$00
sta _sp+1
rts
.scend
; Utility functions. print'dec prints an unsigned 16-bit integer.
; It's ugly and long, mainly because we don't bother with niceties
; like "division". print'string prints a zero-terminated string.
.scope
.data
.org fun'args
.space _val 2
.space _step 2
.space _res 1
.space _allowzero 1
.text
print'dec:
lda #$00
sta _allowzero
lda #<10000
sta _step
lda #>10000
sta _step+1
jsr repsub'16
lda #<1000
sta _step
lda #>1000
sta _step+1
jsr repsub'16
lda #0
sta _step+1
lda #100
sta _step
jsr repsub'16
lda #10
sta _step
jsr repsub'16
lda _val
jsr _print
rts
repsub'16:
lda #$00
sta _res
* lda _val
sec
sbc _step
lda _val+1
sbc _step+1
bcc _done
lda _val
sec
sbc _step
sta _val
lda _val+1
sbc _step+1
sta _val+1
inc _res
jmp -
_done: lda _res
ora _allowzero
beq _ret
sta _allowzero
lda _res
_print: clc
adc #'0
jsr chrout
_ret: rts
.scend
print'string:
ldy #$00
* lda (fun'args), y
beq +
jsr chrout
iny
jmp -
* rts |