mdw@git.distorted.org.uk Git - zx-fizzbuzz/blob - fizzbuzz.s

   1 ;;; -*-asm-*-
   2 ;;;
   3 ;;; Best not to ask why.
   4
   5         org     0xf000
   6
   7 print_a: equ    0x10
   8 tvflag: equ     0x5c3c
   9
  10 entry:
  11         ;; Initialize the buffer.
  12         ld      a, 1
  13         ld      (buf), a
  14         ld      (len), a
  15
  16         ;; Use the main screen.
  17         xor     a
  18         ld      (tvflag), a
  19
  20         ;; Look at the buffer and decide what to do.
  21 again:  ld      e, 0
  22
  23         ;; First, decide whether it's a multiple of three.  This is a bit
  24         ;; fiddly.
  25         ld      a, (len)
  26         ld      b, a
  27         ld      hl, buf
  28         xor     a
  29
  30         ;; Main `mod 3' loop.  Load a byte and add it into the accumulator in
  31         ;; decimal.
  32 mod3:   ld      c, (hl)
  33         inc     hl
  34         add     a, c
  35         daa
  36         jr      nc, mod3_1
  37         call    squish
  38         add     a, 1
  39         daa
  40 mod3_1: djnz    mod3
  41
  42         call    squish
  43         call    squish
  44
  45         cp      0
  46         jr      z, prfizz
  47         cp      3
  48         jr      z, prfizz
  49         cp      6
  50         jr      z, prfizz
  51         cp      9
  52         jr      nz, nofizz
  53
  54 prfizz: ld      hl, fizz
  55         call    print
  56         inc     e
  57
  58         ;; Next, decide whether it's a multiple of five.  This is easier.
  59 nofizz: ld      a, (buf)
  60         and     0x0f
  61         jr      z, prbuzz
  62         cp      5
  63         jr      nz, nobuzz
  64
  65 prbuzz: ld      hl, buzz
  66         call    print
  67         jr      prnl
  68
  69         ;; Not a multiple of five.  Skip ahead if it was a multiple of three.
  70 nobuzz: ld      a, e
  71         cp      0
  72         jr      nz, prnl
  73
  74         ;; OK, so just print the value.
  75         ld      a, (len)
  76         ld      b, 0
  77         ld      c, a
  78         ld      hl, buf - 1
  79         add     hl, bc
  80         ld      b, c
  81
  82         ld      a, (hl)
  83         ld      d, a
  84         srl     a
  85         srl     a
  86         srl     a
  87         srl     a
  88         jr      z, skiplz
  89         or      0x30
  90         rst     print_a
  91 skiplz: ld      a, d
  92         and     0x0f
  93         or      0x30
  94         rst     print_a
  95         dec     b
  96         jr      z, prnl
  97
  98 prdig:  dec     hl
  99         ld      a, (hl)
 100         ld      d, a
 101         srl     a
 102         srl     a
 103         srl     a
 104         srl     a
 105         or      0x30
 106         rst     print_a
 107         ld      a, d
 108         and     0x0f
 109         or      0x30
 110         rst     print_a
 111         djnz    prdig
 112
 113         ;; Print the newline.
 114 prnl:   ld      a, ' '
 115         rst     print_a
 116
 117         ;; Increment the counter.
 118         ld      hl, buf
 119         ld      a, (len)
 120         ld      b, a
 121         scf
 122 incr:   ld      a, (hl)
 123         adc     a, 0
 124         daa
 125         ld      (hl), a
 126         jp      nc, again
 127         inc     hl
 128         djnz    incr
 129
 130         ;; Carry out.
 131         ld      a, (len)
 132         ld      b, 0
 133         ld      c, a
 134         ld      hl, buf
 135         add     hl, bc
 136         ld      (hl), 1
 137         inc     a
 138         ld      (len), a
 139         jp      again
 140
 141 squish:
 142         ;; Add the two halves of a.
 143         ld      c, a
 144         and     0x0f
 145         srl     c
 146         srl     c
 147         srl     c
 148         srl     c
 149         add     a, c
 150         daa
 151         ret
 152
 153 print:
 154         ;; Print the string at hl.
 155         ld      a, (hl)
 156         cp      0
 157         ret     z
 158         rst     print_a
 159         inc     hl
 160         jr      print
 161
 162 fizz:   defb    "fizz", 0
 163 buzz:   defb    "buzz", 0
 164
 165 len:    defb    0
 166 buf:    defs    256