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<span id="L1" class="LineNr"> 1 </span><span class="subxComment">## compute the factorial of 5, and return the result in the exit code</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># To run (from the subx directory):</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># $ subx translate apps/factorial.subx -o apps/factorial</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># $ subx run apps/factorial</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># Expected result:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># $ echo $?</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># 120</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment">#</span>
<span id="L10" class="LineNr"> 10 </span><span class="subxComment"># You can also run the automated test suite:</span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># $ subx run apps/factorial test</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># Expected output:</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># ........</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># Every '.' indicates a passing test. Failing tests get a 'F'.</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment"># When running tests the exit status doesn't mean anything. Yet.</span>
<span id="L16" class="LineNr"> 16 </span>
<span id="L17" class="LineNr"> 17 </span>== code
<span id="L18" class="LineNr"> 18 </span><span class="subxComment"># instruction effective address operand displacement immediate</span>
<span id="L19" class="LineNr"> 19 </span><span class="subxComment"># op subop mod rm32 base index scale r32</span>
<span id="L20" class="LineNr"> 20 </span><span class="subxComment"># 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes</span>
<span id="L21" class="LineNr"> 21 </span>
<span id="L22" class="LineNr"> 22 </span><span class="subxComment"># main:</span>
<span id="L23" class="LineNr"> 23 </span> <span class="subxComment"># prolog</span>
<span id="L24" class="LineNr"> 24 </span> 89/copy 3/mod/direct 5/rm32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/r32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy ESP to EBP</span>
<span id="L25" class="LineNr"> 25 </span> <span class="subxComment"># if (argc > 1)</span>
<span id="L26" class="LineNr"> 26 </span> 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/disp8 1/imm32 <span class="subxComment"># compare *EBP</span>
<span id="L27" class="LineNr"> 27 </span> 7e/jump-if-lesser-or-equal $run-main/disp8
<span id="L28" class="LineNr"> 28 </span> <span class="subxComment"># and if (argv[1] == "test")</span>
<span id="L29" class="LineNr"> 29 </span> <span class="subxComment"># push args</span>
<span id="L30" class="LineNr"> 30 </span> 68/push <span class="Constant">"test"</span>/imm32
<span id="L31" class="LineNr"> 31 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0x8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+8)</span>
<span id="L32" class="LineNr"> 32 </span> <span class="subxComment"># call</span>
<span id="L33" class="LineNr"> 33 </span> e8/call kernel-string-equal/disp32
<span id="L34" class="LineNr"> 34 </span> <span class="subxComment"># discard args</span>
<span id="L35" class="LineNr"> 35 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/imm32 <span class="subxComment"># add to ESP</span>
<span id="L36" class="LineNr"> 36 </span> <span class="subxComment"># check result</span>
<span id="L37" class="LineNr"> 37 </span> 3d/compare-EAX 1/imm32
<span id="L38" class="LineNr"> 38 </span> 75/jump-if-not-equal $run-main/disp8
<span id="L39" class="LineNr"> 39 </span> <span class="subxComment"># then return run-tests()</span>
<span id="L40" class="LineNr"> 40 </span> e8/call run-tests/disp32
<span id="L41" class="LineNr"> 41 </span> 8b/copy 0/mod/indirect 5/rm32/.disp32 <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="Special">Num-test-failures</span>/disp32 <span class="subxComment"># copy *Num-test-failures to EAX</span>
<span id="L42" class="LineNr"> 42 </span> eb/jump $main:end/disp8 <span class="subxComment"># where EAX will get copied to EBX</span>
<span id="L43" class="LineNr"> 43 </span> <span class="subxComment"># else EAX = factorial(5)</span>
<span id="L44" class="LineNr"> 44 </span>$run-main:
<span id="L45" class="LineNr"> 45 </span> <span class="subxComment"># push args</span>
<span id="L46" class="LineNr"> 46 </span> 68/push 5/imm32
<span id="L47" class="LineNr"> 47 </span> <span class="subxComment"># call</span>
<span id="L48" class="LineNr"> 48 </span> e8/call factorial/disp32
<span id="L49" class="LineNr"> 49 </span> <span class="subxComment"># discard args</span>
<span id="L50" class="LineNr"> 50 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/imm32 <span class="subxComment"># add to ESP</span>
<span id="L51" class="LineNr"> 51 </span>$main:end:
<span id="L52" class="LineNr"> 52 </span> <span class="subxComment"># exit(EAX)</span>
<span id="L53" class="LineNr"> 53 </span> 89/copy 3/mod/direct 3/rm32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy EAX to EBX</span>
<span id="L54" class="LineNr"> 54 </span> b8/copy-to-EAX 1/imm32
<span id="L55" class="LineNr"> 55 </span> cd/syscall 0x80/imm8
<span id="L56" class="LineNr"> 56 </span>
<span id="L57" class="LineNr"> 57 </span><span class="subxComment"># factorial(n)</span>
<span id="L58" class="LineNr"> 58 </span>factorial:
<span id="L59" class="LineNr"> 59 </span> <span class="subxComment"># prolog</span>
<span id="L60" class="LineNr"> 60 </span> 55/push-EBP
<span id="L61" class="LineNr"> 61 </span> 89/copy 3/mod/direct 5/rm32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/r32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy ESP to EBP</span>
<span id="L62" class="LineNr"> 62 </span> 53/push-EBX
<span id="L63" class="LineNr"> 63 </span> <span class="subxComment"># initialize EAX to 1 (base case)</span>
<span id="L64" class="LineNr"> 64 </span> b8/copy-to-EAX 1/imm32
<span id="L65" class="LineNr"> 65 </span> <span class="subxComment"># if (n <= 1) jump exit</span>
<span id="L66" class="LineNr"> 66 </span> 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/disp8 1/imm32 <span class="subxComment"># compare *(EBP+8)</span>
<span id="L67" class="LineNr"> 67 </span> 7e/jump-if-<= $factorial:end/disp8
<span id="L68" class="LineNr"> 68 </span> <span class="subxComment"># EBX = n-1</span>
<span id="L69" class="LineNr"> 69 </span> 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 3/r32/EBX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(EBP+8) to EBX</span>
<span id="L70" class="LineNr"> 70 </span> 81 5/subop/subtract 3/mod/direct 3/rm32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 1/imm32 <span class="subxComment"># subtract from EBX</span>
<span id="L71" class="LineNr"> 71 </span> <span class="subxComment"># EAX = factorial(n-1)</span>
<span id="L72" class="LineNr"> 72 </span> <span class="subxComment"># push args</span>
<span id="L73" class="LineNr"> 73 </span> 53/push-EBX
<span id="L74" class="LineNr"> 74 </span> <span class="subxComment"># call</span>
<span id="L75" class="LineNr"> 75 </span> e8/call factorial/disp32
<span id="L76" class="LineNr"> 76 </span> <span class="subxComment"># discard args</span>
<span id="L77" class="LineNr"> 77 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/imm32 <span class="subxComment"># add to ESP</span>
<span id="L78" class="LineNr"> 78 </span> <span class="subxComment"># return n * factorial(n-1)</span>
<span id="L79" class="LineNr"> 79 </span> f7 4/subop/multiply 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># multiply *(EBP+8) into EAX</span>
<span id="L80" class="LineNr"> 80 </span> <span class="subxComment"># TODO: check for overflow</span>
<span id="L81" class="LineNr"> 81 </span>$factorial:end:
<span id="L82" class="LineNr"> 82 </span> <span class="subxComment"># epilog</span>
<span id="L83" class="LineNr"> 83 </span> 5b/pop-to-EBX
<span id="L84" class="LineNr"> 84 </span> 89/copy 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 5/r32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy EBP to ESP</span>
<span id="L85" class="LineNr"> 85 </span> 5d/pop-to-EBP
<span id="L86" class="LineNr"> 86 </span> c3/return
<span id="L87" class="LineNr"> 87 </span>
<span id="L88" class="LineNr"> 88 </span>test-factorial:
<span id="L89" class="LineNr"> 89 </span> <span class="subxComment"># factorial(5)</span>
<span id="L90" class="LineNr"> 90 </span> <span class="subxComment"># push args</span>
<span id="L91" class="LineNr"> 91 </span> 68/push 5/imm32
<span id="L92" class="LineNr"> 92 </span> <span class="subxComment"># call</span>
<span id="L93" class="LineNr"> 93 </span> e8/call factorial/disp32
<span id="L94" class="LineNr"> 94 </span> <span class="subxComment"># discard args</span>
<span id="L95" class="LineNr"> 95 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/imm32 <span class="subxComment"># add to ESP</span>
<span id="L96" class="LineNr"> 96 </span> <span class="subxComment"># check-ints-equal(EAX, 120, failure message)</span>
<span id="L97" class="LineNr"> 97 </span> <span class="subxComment"># push args</span>
<span id="L98" class="LineNr"> 98 </span> 68/push <span class="Constant">"F - test-factorial"</span>/imm32
<span id="L99" class="LineNr"> 99 </span> 68/push 0x78/imm32/expected-120
<span id="L100" class="LineNr">100 </span> 50/push-EAX
<span id="L101" class="LineNr">101 </span> <span class="subxComment"># call</span>
<span id="L102" class="LineNr">102 </span> e8/call check-ints-equal/disp32
<span id="L103" class="LineNr">103 </span> <span class="subxComment"># discard args</span>
<span id="L104" class="LineNr">104 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/imm32 <span class="subxComment"># add to ESP</span>
<span id="L105" class="LineNr">105 </span> <span class="subxComment"># end</span>
<span id="L106" class="LineNr">106 </span> c3/return
<span id="L107" class="LineNr">107 </span>
<span id="L108" class="LineNr">108 </span><span class="subxComment"># vim:nowrap:textwidth=0</span>
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