all repos — xyw @ 0b2088be17b577856b2e5ed21f97c4c4143e0299

A minimal virtual machine and assembler for terminals.

examples/factorial.xyw

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.include "devices.xyw"

; ;ain program: calculate and print factorial of 5
$5 fact JSRw 
print8 JSRw
$0A terminal.output STB
end JMPw

; Factorial subroutine
; a8 -- | [xy]
.label fact
  ; Save argument to both registers
  POPxy
  .label fact.loop 
    PSHy $0 EQU fact.end0 JCNw
    PSHy $1 EQU fact.end1 JCNw
    ; Decrement y and multiply
    DECy PSHx PSHy MULx POPx
    fact.loop JMPw
  .label fact.end0
    ; Edge case: factorial of 0 is 1
    $1
    CLRxy
    RTS
  .label fact.end1
    ; Return result
    PSHx
    CLRxy
    RTS

; Printing subroutine
; a8 -- | [xy]
.label print8
  POPx 
  ; If value is less than 10, print single digit
  PSHx $A LTH print8.single JCNw
  ; Divide by 10: stack becomes [remainder, quotient]
  PSHx $A DIV
  ; Save remainder to y for later
  SWP POPy
  ; Call print8 recursively with quotient (still on stack)
  print8 JSRw
  ; Print the saved remainder
  PSHy $30 ADD terminal.output STB
  CLRxy
  RTS
  .label print8.single
    ; Print single digit
    PSHx $30 ADD terminal.output STB 
    CLRx
    RTS

.label end