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

   1 ;;; -*-asm-*-
   2 ;;;
   3 ;;; Best not to ask why.
   4
   5         ;; Look at the buffer and decide what to do.
   6 again:  ld      e, 0
   7
   8         ;; First, decide whether it's a multiple of three.  This is a bit
   9         ;; fiddly.
  10         ld      a, (len)
  11         ld      b, a
  12         ld      hl, buf
  13         xor     a
  14
  15         ;; Main `mod 3' loop.  Load a byte and add it into the accumulator in
  16         ;; decimal.
  17 mod3:   ld      c, (hl)
  18         inc     hl
  19         add     a, c
  20         daa
  21         jr      nc, mod3_1
  22         call    squish
  23         add     a, 1
  24         daa
  25 mod3_1: djnz    mod3
  26
  27         call    squish
  28         call    squish
  29
  30         and     a
  31         jr      z, prfizz
  32         cp      3
  33         jr      z, prfizz
  34         cp      6
  35         jr      z, prfizz
  36         cp      9
  37         jr      nz, nofizz
  38
  39 prfizz: ld      hl, fizz
  40         call    print
  41         inc     e
  42
  43         ;; Next, decide whether it's a multiple of five.  This is easier.
  44 nofizz: ld      a, (buf)
  45         and     0x0f
  46         jr      z, prbuzz
  47         cp      5
  48         jr      nz, nobuzz
  49
  50 prbuzz: ld      hl, buzz
  51         call    print
  52         jr      prnl
  53
  54         ;; Not a multiple of five.  Skip ahead if it was a multiple of three.
  55 nobuzz: ld      a, e
  56         and     a
  57         jr      nz, prnl
  58
  59         ;; OK, so just print the value.
  60         ld      a, (len)
  61         ld      b, 0
  62         ld      c, a
  63         ld      hl, buf - 1
  64         add     hl, bc
  65         ld      b, c
  66
  67         ld      a, (hl)
  68         ld      d, a
  69         srl     a
  70         srl     a
  71         srl     a
  72         srl     a
  73         jr      z, skiplz
  74         fixdig
  75         print_a
  76 skiplz: ld      a, d
  77         and     0x0f
  78         fixdig
  79         print_a
  80         dec     b
  81         jr      z, prnl
  82
  83 prdig:  dec     hl
  84         ld      a, (hl)
  85         ld      d, a
  86         srl     a
  87         srl     a
  88         srl     a
  89         srl     a
  90         fixdig
  91         print_a
  92         ld      a, d
  93         and     0x0f
  94         fixdig
  95         print_a
  96         djnz    prdig
  97
  98         ;; Print the newline.
  99 prnl:   ld      a, spc
 100         print_a
 101
 102         ;; Increment the counter.
 103         ld      hl, buf
 104         ld      a, (len)
 105         ld      b, a
 106         scf
 107 incr:   ld      a, (hl)
 108         adc     a, 0
 109         daa
 110         ld      (hl), a
 111         jp      nc, again
 112         inc     hl
 113         djnz    incr
 114
 115         ;; Carry out.
 116         ld      a, (len)
 117         ld      b, 0
 118         ld      c, a
 119         ld      hl, buf
 120         add     hl, bc
 121         ld      (hl), 1
 122         inc     a
 123         ld      (len), a
 124         jp      again
 125
 126 squish:
 127         ;; Add the two halves of a.
 128         ld      c, a
 129         and     0x0f
 130         srl     c
 131         srl     c
 132         srl     c
 133         srl     c
 134         add     a, c
 135         daa
 136         ret
 137
 138 print:
 139         ;; Print the string at hl.
 140         ld      a, (hl)
 141         endstrp
 142         ret     z
 143         print_a
 144         inc     hl
 145         jr      print
 146
 147         ;; Initial state.  The buffer notionally continues for another 254
 148         ;; bytes, but there's no point in including them in the image.
 149 len:    db      1
 150 buf:    db      1