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

   1 ;;; -*-asm-*-
   2 ;;; (c) 2021 Mark Wooding
   3 ;;;
   4 ;;; Best not to ask why.
   5
   6 ;;;----- Licensing notice ---------------------------------------------------
   7 ;;;
   8 ;;; This file is part of ZX Fizzbuzz.
   9 ;;;
  10 ;;; ZX Fizzbuzz is free software: you can redistribute it and/or modify it
  11 ;;; under the terms of the GNU Lesser General Public License as published
  12 ;;; by the Free Software Foundation; either version 3 of the License, or
  13 ;;; (at your option) any later version.
  14 ;;;
  15 ;;; ZX Fizzbuzz is distributed in the hope that it will be useful, but
  16 ;;; WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  18 ;;; Lesser General Public License for more details.
  19 ;;;
  20 ;;; You should have received a copy of the GNU Lesser General Public
  21 ;;; License along with ZX Fizzbuzz.  If not, see
  22 ;;; <https://www.gnu.org/licenses/>.
  23
  24         ;; Look at the buffer and decide what to do.
  25 again:  ld      e, 0
  26
  27         ;; First, decide whether it's a multiple of three.  This is a bit
  28         ;; fiddly.
  29         ld      a, (len)
  30         ld      b, a
  31         ld      hl, buf
  32         xor     a
  33
  34         ;; Main `mod 3' loop.  Load a byte and add it into the accumulator in
  35         ;; decimal.
  36 mod3:   ld      c, (hl)
  37         inc     hl
  38         add     a, c
  39         daa
  40         jr      nc, mod3_1
  41         call    squish
  42         add     a, 1
  43         daa
  44 mod3_1: djnz    mod3
  45
  46         call    squish
  47         call    squish
  48
  49         and     a
  50         jr      z, prfizz
  51         cp      3
  52         jr      z, prfizz
  53         cp      6
  54         jr      z, prfizz
  55         cp      9
  56         jr      nz, nofizz
  57
  58 prfizz: ld      hl, fizz
  59         call    print
  60         inc     e
  61
  62         ;; Next, decide whether it's a multiple of five.  This is easier.
  63 nofizz: ld      a, (buf)
  64         and     0x0f
  65         jr      z, prbuzz
  66         cp      5
  67         jr      nz, nobuzz
  68
  69 prbuzz: ld      hl, buzz
  70         call    print
  71         jr      prnl
  72
  73         ;; Not a multiple of five.  Skip ahead if it was a multiple of three.
  74 nobuzz: ld      a, e
  75         and     a
  76         jr      nz, prnl
  77
  78         ;; OK, so just print the value.
  79         ld      hl, buf - 1
  80         ld      bc, (len)
  81         add     hl, bc
  82         ld      b, c
  83
  84         ld      a, (hl)
  85         ld      d, a
  86         srl     a
  87         srl     a
  88         srl     a
  89         srl     a
  90         jr      z, skiplz
  91         fixdig
  92         print_a
  93 skiplz: ld      a, d
  94         and     0x0f
  95         fixdig
  96         print_a
  97         dec     b
  98         jr      z, prnl
  99
 100 prdig:  dec     hl
 101         ld      a, (hl)
 102         ld      d, a
 103         srl     a
 104         srl     a
 105         srl     a
 106         srl     a
 107         fixdig
 108         print_a
 109         ld      a, d
 110         and     0x0f
 111         fixdig
 112         print_a
 113         djnz    prdig
 114
 115         ;; Print the newline.
 116 prnl:   ld      a, spc
 117         print_a
 118
 119         ;; Increment the counter.
 120         ld      hl, buf
 121         ld      a, (len)
 122         ld      b, a
 123         scf
 124 incr:   ld      a, (hl)
 125         adc     a, 0
 126         daa
 127         ld      (hl), a
 128         jp      nc, again
 129         inc     hl
 130         djnz    incr
 131
 132         ;; Carry out.
 133         ld      (hl), 1
 134         ld      hl, len
 135         inc     (hl)
 136         jp      again
 137
 138 squish:
 139         ;; Add the two halves of a.
 140         ld      c, a
 141         and     0x0f
 142         srl     c
 143         srl     c
 144         srl     c
 145         srl     c
 146         add     a, c
 147         daa
 148         ret
 149
 150 print:
 151         ;; Print the string at hl.
 152         ld      a, (hl)
 153         endstrp
 154         ret     z
 155         print_a
 156         inc     hl
 157         jr      print
 158
 159         ;; Initial state.  The buffer notionally continues for another 254
 160         ;; bytes, but there's no point in including them in the image.
 161 len:    db      1, 0
 162 buf:    db      1