Fibonacci for S65

fib.asm

@0x00

ORIGIN = 0xFF8D

==Start==
LDA #1		; start counting at 1
{
  PHA		; save A
  JSR Fib
  CMP 0x0200	; if fib(A)>fib(A-1), stop
  BCC BR
  STA 0x0200
  JSR Printn
  JSR Newline
  PLA		; restore A
  ADC #1	; increase A by 1
  JMP RE
}
{JMP RE}

==Fib==
LDX #1
LDY #0
{
  CMP #2
  BCC BR
  SBC #1	; decrement A
  PHA		; save A
  TXA		; set A to X
  STY 0x0201	; add Y to A
  CLC
  ADC 0x0201
  STX 0x0201	; set Y to X
  LDY 0x0201
  TAX		; set X to A
  PLA		; restore A
  JMP RE
}
TXA
RTS

==Printn==
{
  PHA		; save A
  LSR A		; divide A by 10...
  STA 0x0201
  LSR A
  ADC 0x0201
  ROR A
  LSR A
  LSR A
  ADC 0x0201
  ROR A
  ADC 0x0201
  ROR A
  LSR A
  LSR A
  BEQ BR	; stop if A = 0
  JSR Printn	; recursively call Printn
}
PLA		; restore A
{
  CMP #10	; break if A < 10
  BCC BR
  SBC #10	; subtract 10 from A
  JMP RE	; and loop
}
ORA #0x30	; ASCII code for '0'
STA 0x7c00	; print digit
RTS

==Newline==
LDA #13
STA 0x7c00
RTS

==Irq==
RTI

@0xFFFC
DATA Start
DATA Irq