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<a href='https://github.com/akkartik/mu/blob/main/linux/apps/factorial4.subx'>https://github.com/akkartik/mu/blob/main/linux/apps/factorial4.subx</a>
<pre id='vimCodeElement'>
<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"># Uses syntax sugar for:</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># rm32 operands</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># function calls</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># control flow</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment">#</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># To run:</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># $ ./translate_subx init.linux [01]*.subx apps/factorial4.subx</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment"># $ ./a.elf</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment"># Expected result:</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment"># $ echo $?</span>
<span id="L13" class="LineNr">13 </span><span class="subxComment"># 120</span>
<span id="L14" class="LineNr">14 </span><span class="subxComment">#</span>
<span id="L15" class="LineNr">15 </span><span class="subxComment"># You can also run the automated test suite:</span>
<span id="L16" class="LineNr">16 </span><span class="subxComment"># $ ./a.elf test</span>
<span id="L17" class="LineNr">17 </span><span class="subxComment"># Expected output:</span>
<span id="L18" class="LineNr">18 </span><span class="subxComment"># ........</span>
<span id="L19" class="LineNr">19 </span><span class="subxComment"># Every '.' indicates a passing test. Failing tests get a 'F'.</span>
<span id="L20" class="LineNr">20 </span><span class="subxComment">#</span>
<span id="L21" class="LineNr">21 </span><span class="subxComment"># Compare factorial3.subx</span>
<span id="L22" class="LineNr">22 </span>
<span id="L23" class="LineNr">23 </span>== code
<span id="L24" class="LineNr">24 </span>
<span id="L25" class="LineNr">25 </span><span class="subxFunction">factorial</span>: <span class="subxComment"># n: int -> _/eax: int</span>
<span id="L26" class="LineNr">26 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L27" class="LineNr">27 </span> 55/push-ebp
<span id="L28" class="LineNr">28 </span> 89/<- %ebp 4/r32/esp
<span id="L29" class="LineNr">29 </span> <span class="subxComment"># save registers</span>
<span id="L30" class="LineNr">30 </span> 51/push-ecx
<span id="L31" class="LineNr">31 </span> <span class="subxComment"># if (n <= 1) return 1</span>
<span id="L32" class="LineNr">32 </span> 81 7/subop/compare *(ebp+8) 1/imm32
<span id="L33" class="LineNr">33 </span> {
<span id="L34" class="LineNr">34 </span> 7f/jump-if-> <span class="Constant">break</span>/disp8
<span id="L35" class="LineNr">35 </span> b8/copy-to-eax 1/imm32
<span id="L36" class="LineNr">36 </span> eb/jump $factorial:end/disp8
<span id="L37" class="LineNr">37 </span> }
<span id="L38" class="LineNr">38 </span> <span class="subxComment"># n > 1; return n * factorial(n-1)</span>
<span id="L39" class="LineNr">39 </span> 8b/-> *(ebp+8) 1/r32/ecx
<span id="L40" class="LineNr">40 </span> 49/decrement-ecx
<span id="L41" class="LineNr">41 </span> (<a href='factorial4.subx.html#L25'>factorial</a> %ecx) <span class="subxComment"># => eax</span>
<span id="L42" class="LineNr">42 </span> f7 4/subop/multiply-into-eax *(ebp+8)
<span id="L43" class="LineNr">43 </span> <span class="subxComment"># TODO: check for overflow</span>
<span id="L44" class="LineNr">44 </span><span class="Constant">$factorial:end</span>:
<span id="L45" class="LineNr">45 </span> <span class="subxComment"># restore registers</span>
<span id="L46" class="LineNr">46 </span> 59/pop-to-ecx
<span id="L47" class="LineNr">47 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L48" class="LineNr">48 </span> 89/<- %esp 5/r32/ebp
<span id="L49" class="LineNr">49 </span> 5d/pop-to-ebp
<span id="L50" class="LineNr">50 </span> c3/return
<span id="L51" class="LineNr">51 </span>
<span id="L52" class="LineNr">52 </span><span class="subxTest">test-factorial</span>:
<span id="L53" class="LineNr">53 </span> (<a href='factorial4.subx.html#L25'>factorial</a> 5)
<span id="L54" class="LineNr">54 </span> (<a href='../102test.subx.html#L23'>check-ints-equal</a> %eax 0x78 <span class="Constant">"F - test-factorial"</span>)
<span id="L55" class="LineNr">55 </span> c3/return
<span id="L56" class="LineNr">56 </span>
<span id="L57" class="LineNr">57 </span><span class="SpecialChar">Entry</span>: <span class="subxComment"># run tests if necessary, compute `factorial(5)` if not</span>
<span id="L58" class="LineNr">58 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L59" class="LineNr">59 </span> 89/<- %ebp 4/r32/esp
<span id="L60" class="LineNr">60 </span>
<span id="L61" class="LineNr">61 </span> <span class="subxComment"># initialize heap (needed by tests elsewhere)</span>
<span id="L62" class="LineNr">62 </span> (<a href='../104new-segment.subx.html#L40'>new-segment</a> *<span class="SpecialChar"><a href='../120allocate.subx.html#L34'>Heap-size</a></span> <span class="SpecialChar"><a href='../120allocate.subx.html#L27'>Heap</a></span>)
<span id="L63" class="LineNr">63 </span>
<span id="L64" class="LineNr">64 </span> <span class="subxComment"># if (argc <= 1) return factorial(5)</span>
<span id="L65" class="LineNr">65 </span> {
<span id="L66" class="LineNr">66 </span> <span class="subxComment"># if (argc > 1) break</span>
<span id="L67" class="LineNr">67 </span> 81 7/subop/compare *ebp 1/imm32
<span id="L68" class="LineNr">68 </span> 7f/jump-if-> <span class="Constant">break</span>/disp8
<span id="L69" class="LineNr">69 </span> <span class="subxComment"># ebx = factorial(5)</span>
<span id="L70" class="LineNr">70 </span> (<a href='factorial4.subx.html#L25'>factorial</a> 5) <span class="subxComment"># => eax</span>
<span id="L71" class="LineNr">71 </span> 89/<- %ebx 0/r32/eax
<span id="L72" class="LineNr">72 </span> eb/jump $main:end/disp8
<span id="L73" class="LineNr">73 </span> }
<span id="L74" class="LineNr">74 </span> <span class="subxComment"># otherwise if first arg is "test", then return run_tests()</span>
<span id="L75" class="LineNr">75 </span> {
<span id="L76" class="LineNr">76 </span> <span class="subxComment"># if (!kernel-string-equal?(argv[1], "test")) break</span>
<span id="L77" class="LineNr">77 </span> (<a href='../103kernel-string-equal.subx.html#L31'>kernel-string-equal?</a> *(ebp+8) <span class="Constant">"test"</span>) <span class="subxComment"># => eax</span>
<span id="L78" class="LineNr">78 </span> 3d/compare-eax-and 0/imm32/false
<span id="L79" class="LineNr">79 </span> 74/jump-if-= <span class="Constant">break</span>/disp8
<span id="L80" class="LineNr">80 </span> <span class="subxComment">#</span>
<span id="L81" class="LineNr">81 </span> (run-tests)
<span id="L82" class="LineNr">82 </span> <span class="subxComment"># exit(*Num-test-failures)</span>
<span id="L83" class="LineNr">83 </span> 8b/-> *<span class="SpecialChar"><a href='../102test.subx.html#L89'>Num-test-failures</a></span> 3/r32/ebx
<span id="L84" class="LineNr">84 </span> eb/jump $main:end/disp8
<span id="L85" class="LineNr">85 </span> }
<span id="L86" class="LineNr">86 </span> bb/copy-to-ebx 0/imm32
<span id="L87" class="LineNr">87 </span><span class="Constant">$main:end</span>:
<span id="L88" class="LineNr">88 </span> e8/call <a href='../000init.subx.html#L18'>syscall_exit</a>/disp32
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