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<a href='https://github.com/akkartik/mu/blob/main/linux/bootstrap/000organization.cc'>https://github.com/akkartik/mu/blob/main/linux/bootstrap/000organization.cc</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="Comment">//: You guessed right: the '000' prefix means you should start reading here.</span>
<span id="L2" class="LineNr"> 2 </span><span class="Comment">//:</span>
<span id="L3" class="LineNr"> 3 </span><span class="Comment">//: This project is set up to load all files with a numeric prefix. Just</span>
<span id="L4" class="LineNr"> 4 </span><span class="Comment">//: create a new file and start hacking.</span>
<span id="L5" class="LineNr"> 5 </span><span class="Comment">//:</span>
<span id="L6" class="LineNr"> 6 </span><span class="Comment">//: The first few files (00*) are independent of what this program does, an</span>
<span id="L7" class="LineNr"> 7 </span><span class="Comment">//: experimental skeleton that will hopefully make it both easier for others to</span>
<span id="L8" class="LineNr"> 8 </span><span class="Comment">//: understand and more malleable, easier to rewrite and remould into radically</span>
<span id="L9" class="LineNr"> 9 </span><span class="Comment">//: different shapes without breaking in subtle corner cases. The premise is</span>
<span id="L10" class="LineNr"> 10 </span><span class="Comment">//: that understandability and rewrite-friendliness are related in a virtuous</span>
<span id="L11" class="LineNr"> 11 </span><span class="Comment">//: cycle. Doing one well makes it easier to do the other.</span>
<span id="L12" class="LineNr"> 12 </span><span class="Comment">//:</span>
<span id="L13" class="LineNr"> 13 </span><span class="Comment">//: Lower down, this file contains a legal, bare-bones C++ program. It doesn't</span>
<span id="L14" class="LineNr"> 14 </span><span class="Comment">//: do anything yet; subsequent files will contain :(...) directives to insert</span>
<span id="L15" class="LineNr"> 15 </span><span class="Comment">//: lines into it. For example:</span>
<span id="L16" class="LineNr"> 16 </span><span class="Comment">//: :(after "more events")</span>
<span id="L17" class="LineNr"> 17 </span><span class="Comment">//: This directive means: insert the following lines after a line in the</span>
<span id="L18" class="LineNr"> 18 </span><span class="Comment">//: program containing the words "more events".</span>
<span id="L19" class="LineNr"> 19 </span><span class="Comment">//:</span>
<span id="L20" class="LineNr"> 20 </span><span class="Comment">//: A simple tool is included to 'tangle' all the files together in sequence</span>
<span id="L21" class="LineNr"> 21 </span><span class="Comment">//: according to their directives into a single source file containing all the</span>
<span id="L22" class="LineNr"> 22 </span><span class="Comment">//: code for the project, and then feed the source file to the compiler.</span>
<span id="L23" class="LineNr"> 23 </span><span class="Comment">//: (It'll drop these comments starting with a '//:' prefix that only make</span>
<span id="L24" class="LineNr"> 24 </span><span class="Comment">//: sense before tangling.)</span>
<span id="L25" class="LineNr"> 25 </span><span class="Comment">//:</span>
<span id="L26" class="LineNr"> 26 </span><span class="Comment">//: Directives free up the programmer to order code for others to read rather</span>
<span id="L27" class="LineNr"> 27 </span><span class="Comment">//: than as forced by the computer or compiler. Each individual feature can be</span>
<span id="L28" class="LineNr"> 28 </span><span class="Comment">//: organized in a self-contained 'layer' that adds code to many different data</span>
<span id="L29" class="LineNr"> 29 </span><span class="Comment">//: structures and functions all over the program. The right decomposition into</span>
<span id="L30" class="LineNr"> 30 </span><span class="Comment">//: layers will let each layer make sense in isolation.</span>
<span id="L31" class="LineNr"> 31 </span><span class="Comment">//:</span>
<span id="L32" class="LineNr"> 32 </span><span class="Comment">//: "If I look at any small part of it, I can see what is going on -- I don't</span>
<span id="L33" class="LineNr"> 33 </span><span class="Comment">//: need to refer to other parts to understand what something is doing.</span>
<span id="L34" class="LineNr"> 34 </span><span class="Comment">//:</span>
<span id="L35" class="LineNr"> 35 </span><span class="Comment">//: If I look at any large part in overview, I can see what is going on -- I</span>
<span id="L36" class="LineNr"> 36 </span><span class="Comment">//: don't need to know all the details to get it.</span>
<span id="L37" class="LineNr"> 37 </span><span class="Comment">//:</span>
<span id="L38" class="LineNr"> 38 </span><span class="Comment">//: Every level of detail is as locally coherent and as well thought-out as</span>
<span id="L39" class="LineNr"> 39 </span><span class="Comment">//: any other level."</span>
<span id="L40" class="LineNr"> 40 </span><span class="Comment">//:</span>
<span id="L41" class="LineNr"> 41 </span><span class="Comment">//: -- Richard Gabriel, "The Quality Without A Name"</span>
<span id="L42" class="LineNr"> 42 </span><span class="Comment">//: (<a href="http://dreamsongs.com/Files/PatternsOfSoftware.pdf">http://dreamsongs.com/Files/PatternsOfSoftware.pdf</a>, page 42)</span>
<span id="L43" class="LineNr"> 43 </span><span class="Comment">//:</span>
<span id="L44" class="LineNr"> 44 </span><span class="Comment">//: Directives are powerful; they permit inserting or modifying any point in</span>
<span id="L45" class="LineNr"> 45 </span><span class="Comment">//: the program. Using them tastefully requires mapping out specific lines as</span>
<span id="L46" class="LineNr"> 46 </span><span class="Comment">//: waypoints for future layers to hook into. Often such waypoints will be in</span>
<span id="L47" class="LineNr"> 47 </span><span class="Comment">//: comments, capitalized to hint that other layers rely on their presence.</span>
<span id="L48" class="LineNr"> 48 </span><span class="Comment">//:</span>
<span id="L49" class="LineNr"> 49 </span><span class="Comment">//: A single waypoint might have many different code fragments hooking into</span>
<span id="L50" class="LineNr"> 50 </span><span class="Comment">//: it from all over the codebase. Use 'before' directives to insert</span>
<span id="L51" class="LineNr"> 51 </span><span class="Comment">//: code at a location in order, top to bottom, and 'after' directives to</span>
<span id="L52" class="LineNr"> 52 </span><span class="Comment">//: insert code in reverse order. By convention waypoints intended for insertion</span>
<span id="L53" class="LineNr"> 53 </span><span class="Comment">//: before begin with 'End'. Notice below how the layers line up above the "End</span>
<span id="L54" class="LineNr"> 54 </span><span class="Comment">//: Foo" waypoint.</span>
<span id="L55" class="LineNr"> 55 </span><span class="Comment">//:</span>
<span id="L56" class="LineNr"> 56 </span><span class="Comment">//: File 001 File 002 File 003</span>
<span id="L57" class="LineNr"> 57 </span><span class="Comment">//: ============ =================== ===================</span>
<span id="L58" class="LineNr"> 58 </span><span class="Comment">//: // Foo</span>
<span id="L59" class="LineNr"> 59 </span><span class="Comment">//: ------------</span>
<span id="L60" class="LineNr"> 60 </span><span class="Comment">//: <---- :(before "End Foo")</span>
<span id="L61" class="LineNr"> 61 </span><span class="Comment">//: ....</span>
<span id="L62" class="LineNr"> 62 </span><span class="Comment">//: ...</span>
<span id="L63" class="LineNr"> 63 </span><span class="Comment">//: ------------</span>
<span id="L64" class="LineNr"> 64 </span><span class="Comment">//: <---------------------------- :(before "End Foo")</span>
<span id="L65" class="LineNr"> 65 </span><span class="Comment">//: ....</span>
<span id="L66" class="LineNr"> 66 </span><span class="Comment">//: ...</span>
<span id="L67" class="LineNr"> 67 </span><span class="Comment">//: // End Foo</span>
<span id="L68" class="LineNr"> 68 </span><span class="Comment">//: ============</span>
<span id="L69" class="LineNr"> 69 </span><span class="Comment">//:</span>
<span id="L70" class="LineNr"> 70 </span><span class="Comment">//: Here's part of a layer in color: <a href="http://i.imgur.com/0eONnyX.png">http://i.imgur.com/0eONnyX.png</a>. Directives</span>
<span id="L71" class="LineNr"> 71 </span><span class="Comment">//: are shaded dark.</span>
<span id="L72" class="LineNr"> 72 </span><span class="Comment">//:</span>
<span id="L73" class="LineNr"> 73 </span><span class="Comment">//: Layers do more than just shuffle code around. In a well-organized codebase</span>
<span id="L74" class="LineNr"> 74 </span><span class="Comment">//: it should be possible to stop loading after any file/layer, build and run</span>
<span id="L75" class="LineNr"> 75 </span><span class="Comment">//: the program, and pass all tests for loaded features. (Relevant is</span>
<span id="L76" class="LineNr"> 76 </span><span class="Comment">//: <a href="http://youtube.com/watch?v=c8N72t7aScY">http://youtube.com/watch?v=c8N72t7aScY</a>, a scene from "2001: A Space</span>
<span id="L77" class="LineNr"> 77 </span><span class="Comment">//: Odyssey".) Get into the habit of running the included script called</span>
<span id="L78" class="LineNr"> 78 </span><span class="Comment">//: 'test_layers' before you commit any changes.</span>
<span id="L79" class="LineNr"> 79 </span><span class="Comment">//:</span>
<span id="L80" class="LineNr"> 80 </span><span class="Comment">//: This 'subsetting guarantee' ensures that this directory contains a</span>
<span id="L81" class="LineNr"> 81 </span><span class="Comment">//: cleaned-up narrative of the evolution of this codebase. Organizing</span>
<span id="L82" class="LineNr"> 82 </span><span class="Comment">//: autobiographically allows newcomers to rapidly orient themselves, reading</span>
<span id="L83" class="LineNr"> 83 </span><span class="Comment">//: the first few files to understand a simple gestalt of a program's core</span>
<span id="L84" class="LineNr"> 84 </span><span class="Comment">//: purpose and features, and later gradually working their way through other</span>
<span id="L85" class="LineNr"> 85 </span><span class="Comment">//: features as the need arises.</span>
<span id="L86" class="LineNr"> 86 </span><span class="Comment">//:</span>
<span id="L87" class="LineNr"> 87 </span><span class="Comment">//: Programmers shouldn't need to understand everything about a program to</span>
<span id="L88" class="LineNr"> 88 </span><span class="Comment">//: hack on it. But they shouldn't be prevented from a thorough understanding</span>
<span id="L89" class="LineNr"> 89 </span><span class="Comment">//: of each aspect either. The goal of layers is to reward curiosity.</span>
<span id="L90" class="LineNr"> 90 </span><span class="Comment">//:</span>
<span id="L91" class="LineNr"> 91 </span><span class="Comment">//: More information: <a href="http://akkartik.name/post/wart-layers">http://akkartik.name/post/wart-layers</a></span>
<span id="L92" class="LineNr"> 92 </span>
<span id="L93" class="LineNr"> 93 </span><span class="Comment">// Includes</span>
<span id="L94" class="LineNr"> 94 </span><span class="Comment">// End Includes</span>
<span id="L95" class="LineNr"> 95 </span>
<span id="L96" class="LineNr"> 96 </span><span class="Comment">// Types</span>
<span id="L97" class="LineNr"> 97 </span><span class="Comment">// End Types</span>
<span id="L98" class="LineNr"> 98 </span>
<span id="L99" class="LineNr"> 99 </span><span class="Comment">// Function prototypes are auto-generated in the 'build' script; define your</span>
<span id="L100" class="LineNr">100 </span><span class="Comment">// functions in any order. Just be sure to declare each function header all on</span>
<span id="L101" class="LineNr">101 </span><span class="Comment">// one line, ending with the '{'. Our auto-generation scripts are too minimal</span>
<span id="L102" class="LineNr">102 </span><span class="Comment">// and simple-minded to handle anything else.</span>
<span id="L103" class="LineNr">103 </span><span class="PreProc">#include </span><span class="Constant">"function_list"</span> <span class="Comment">// by convention, files ending with '_list' are auto-generated</span>
<span id="L104" class="LineNr">104 </span>
<span id="L105" class="LineNr">105 </span><span class="Comment">// Globals</span>
<span id="L106" class="LineNr">106 </span><span class="Comment">//</span>
<span id="L107" class="LineNr">107 </span><span class="Comment">// All statements in this section should always define a single variable on a</span>
<span id="L108" class="LineNr">108 </span><span class="Comment">// single line. The 'build' script will simple-mindedly auto-generate extern</span>
<span id="L109" class="LineNr">109 </span><span class="Comment">// declarations for them. Remember to define (not just declare) constants with</span>
<span id="L110" class="LineNr">110 </span><span class="Comment">// extern linkage in this section, since C++ global constants have internal</span>
<span id="L111" class="LineNr">111 </span><span class="Comment">// linkage by default.</span>
<span id="L112" class="LineNr">112 </span><span class="Comment">//</span>
<span id="L113" class="LineNr">113 </span><span class="Comment">// End Globals</span>
<span id="L114" class="LineNr">114 </span>
<span id="L115" class="LineNr">115 </span><span class="Normal">int</span> <a href='000organization.cc.html#L115'>main</a><span class="Delimiter">(</span><span class="Normal">int</span> argc<span class="Delimiter">,</span> <span class="Normal">char</span>* argv[]<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L116" class="LineNr">116 </span> atexit<span class="Delimiter">(</span><a href='000organization.cc.html#L150'>reset</a><span class="Delimiter">);</span>
<span id="L117" class="LineNr">117 </span> <span class="Comment">// we require a 32-bit little-endian system</span>
<span id="L118" class="LineNr">118 </span> assert<span class="Delimiter">(</span><span class="Normal">sizeof</span><span class="Delimiter">(</span><span class="Normal">int</span><span class="Delimiter">)</span> == <span class="Constant">4</span><span class="Delimiter">);</span>
<span id="L119" class="LineNr">119 </span> assert<span class="Delimiter">(</span><span class="Normal">sizeof</span><span class="Delimiter">(</span><span class="Normal">float</span><span class="Delimiter">)</span> == <span class="Constant">4</span><span class="Delimiter">);</span>
<span id="L120" class="LineNr">120 </span> <a href='000organization.cc.html#L154'>assert_little_endian</a><span class="Delimiter">();</span>
<span id="L121" class="LineNr">121 </span>
<span id="L122" class="LineNr">122 </span> <span class="Comment">// End One-time Setup</span>
<span id="L123" class="LineNr">123 </span>
<span id="L124" class="LineNr">124 </span> <span class="Comment">// Commandline Parsing</span>
<span id="L125" class="LineNr">125 </span> <span class="Comment">// End Commandline Parsing</span>
<span id="L126" class="LineNr">126 </span>
<span id="L127" class="LineNr">127 </span> <span class="Comment">// End Main</span>
<span id="L128" class="LineNr">128 </span>
<span id="L129" class="LineNr">129 </span> <span class="Identifier">return</span> <span class="Constant">0</span><span class="Delimiter">;</span>
<span id="L130" class="LineNr">130 </span><span class="Delimiter">}</span>
<span id="L131" class="LineNr">131 </span>
<span id="L132" class="LineNr">132 </span><span class="Comment">// Unit Tests</span>
<span id="L133" class="LineNr">133 </span><span class="Comment">// End Unit Tests</span>
<span id="L134" class="LineNr">134 </span>
<span id="L135" class="LineNr">135 </span><span class="Comment">//: our first directive; insert the following headers at the start of the program</span>
<span id="L136" class="LineNr">136 </span><span class="Delimiter">:(before "End Includes")</span>
<span id="L137" class="LineNr">137 </span><span class="PreProc">#include </span><span class="Constant"><assert.h></span>
<span id="L138" class="LineNr">138 </span><span class="PreProc">#include </span><span class="Constant"><stdlib.h></span>
<span id="L139" class="LineNr">139 </span>
<span id="L140" class="LineNr">140 </span><span class="Comment">//: Without directives or with the :(code) directive, lines get added at the</span>
<span id="L141" class="LineNr">141 </span><span class="Comment">//: end.</span>
<span id="L142" class="LineNr">142 </span><span class="Comment">//:</span>
<span id="L143" class="LineNr">143 </span><span class="Comment">//: Regardless of where functions are defined, we can call them anywhere we</span>
<span id="L144" class="LineNr">144 </span><span class="Comment">//: like as long as we format the function header in a specific way: put it</span>
<span id="L145" class="LineNr">145 </span><span class="Comment">//: all on a single line without indent, end the line with ') {' and no</span>
<span id="L146" class="LineNr">146 </span><span class="Comment">//: trailing whitespace. As long as functions uniformly start this way, our</span>
<span id="L147" class="LineNr">147 </span><span class="Comment">//: 'build' script contains a little command to automatically generate</span>
<span id="L148" class="LineNr">148 </span><span class="Comment">//: declarations for them.</span>
<span id="L149" class="LineNr">149 </span><span class="Delimiter">:(code)</span>
<span id="L150" class="LineNr">150 </span><span class="Normal">void</span> <a href='000organization.cc.html#L150'>reset</a><span class="Delimiter">()</span> <span class="Delimiter">{</span>
<span id="L151" class="LineNr">151 </span> <span class="Comment">// End Reset</span>
<span id="L152" class="LineNr">152 </span><span class="Delimiter">}</span>
<span id="L153" class="LineNr">153 </span>
<span id="L154" class="LineNr">154 </span><span class="Normal">void</span> <a href='000organization.cc.html#L154'>assert_little_endian</a><span class="Delimiter">()</span> <span class="Delimiter">{</span>
<span id="L155" class="LineNr">155 </span> <span class="Normal">const</span> <span class="Normal">int</span> x = <span class="Constant">1</span><span class="Delimiter">;</span>
<span id="L156" class="LineNr">156 </span> <span class="Normal">const</span> <span class="Normal">char</span>* y = <span class="Normal">reinterpret_cast</span><<span class="Normal">const</span> <span class="Normal">char</span>*><span class="Delimiter">(</span>&x<span class="Delimiter">);</span>
<span id="L157" class="LineNr">157 </span> <span class="Normal">if</span> <span class="Delimiter">(</span>*y != <span class="Constant">1</span><span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L158" class="LineNr">158 </span> cerr << <span class="Constant">"SubX requires a little-endian processor. Do you have Intel (or AMD or Atom) inside?</span><span class="cSpecial">\n</span><span class="Constant">"</span><span class="Delimiter">;</span>
<span id="L159" class="LineNr">159 </span> exit<span class="Delimiter">(</span><span class="Constant">1</span><span class="Delimiter">);</span>
<span id="L160" class="LineNr">160 </span> <span class="Delimiter">}</span>
<span id="L161" class="LineNr">161 </span><span class="Delimiter">}</span>
<span id="L162" class="LineNr">162 </span><span class="Delimiter">:(before "End Includes")</span>
<span id="L163" class="LineNr">163 </span><span class="PreProc">#include</span><span class="Constant"><iostream></span>
<span id="L164" class="LineNr">164 </span><span class="Normal">using</span> std::cerr<span class="Delimiter">;</span>
</pre>
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