Aiden Fox Ivey's blog. Zola 2025-12-05T00:00:00+00:00 https://aidenfoxivey.com/atom.xml 2025-12-05T00:00:00+00:00 2025-12-05T00:00:00+00:00 Aiden Fox Ivey https://aidenfoxivey.com/posts/iongraph/ <p>I originally wrote this on railsatscale.com during my internship. It may be of interest. :)</p> <p>Also note <a rel="external" href="https://spidermonkey.dev/blog/2025/10/28/iongraph-web.html">https://spidermonkey.dev/blog/2025/10/28/iongraph-web.html</a></p> <p><a rel="external" href="https://railsatscale.com/2025-11-19-adding-iongraph-support/">https://railsatscale.com/2025-11-19-adding-iongraph-support/</a></p> <p>Update:</p> <p>I got featured on Ruby Weekly Issue 779 😁</p> <p><a rel="external" href="https://rubyweekly.com/issues/779">https://rubyweekly.com/issues/779</a></p> 2025-09-30T00:00:00+00:00 2025-09-30T00:00:00+00:00 Aiden Fox Ivey https://aidenfoxivey.com/posts/usingthefishshell/ <p><a rel="external" href="https://www.flickr.com/photos/anujraj/3518252658"><img src="/img/gonefishing.png" alt="" /></a></p> <p>I’ve used <a rel="external" href="https://fishshell.com/">Fish shell</a> for the past few years now and find it pretty useful.<sup class="footnote-reference" id="fr-disclaimer-1"><a href="#fn-disclaimer">1</a></sup> I was originally convinced by <a rel="external" href="https://jvns.ca/blog/2017/04/23/the-fish-shell-is-awesome/">Julia Evans’ <em>The fish shell is awesome</em></a>. Lately, she has the follow up <a rel="external" href="https://jvns.ca/blog/2024/09/12/reasons-i--still--love-fish/"><em>Reasons I still love the fish shell</em></a>. These are both worth reading - and just generally her posts. She’s a very, very good explainer at plenty of concepts that are hard.</p> <p>The tl;dr from these articles is that Fish has good multiline support for pasting, good tab completion, good auto suggestions, and decent command history (she reports 256000).</p> <p>I actually have a few more to add on to that - mostly rehashing the Fish documentation page, but with <a rel="external" href="https://asciinema.org/">asciinema</a> recordings of the commands.<sup class="footnote-reference" id="fr-disclaimer2-1"><a href="#fn-disclaimer2">2</a></sup></p> <p>I think of learning how to use the Fish shell interactively as becoming faster at doing routine things within my job and also regular work. These are often annoying things to do. I don’t really have a scientific argument to make here about any relative speedups. I mostly use Fish because I find it more comfortable. It also saves me time because there’s a pre-existing “way to do things”. There are a lot of decisions to be made in engineering, but the minute specifics of how I interact with my shell is not one of them <em>yet</em>.</p> <p>Here’s some classics:</p> <h2 id="tab-and-shift-tab">tab and shift-tab</h2> <script src="https://asciinema.org/a/9W9y04niHoWmFDqLGH3EtiWaI.js" id="asciicast-9W9y04niHoWmFDqLGH3EtiWaI" async="true"></script> <p>Here I demonstrate just how nice the tab interface is for the Fish shell. Notice that after having started the <code>-</code>, Fish “knows” to complete commands and prints them to tab through them with brief explanations of each command. From what I understand, Fish starts by <a rel="external" href="https://fishshell.com/docs/current/cmds/fish_update_completions.html">parsing the <code>man</code> pages</a> of each command and maintains a database it looks up from.</p> <h2 id="arrow-keys">arrow keys</h2> <p>In Fish, you can use the arrow keys to move around the shell. This is identical to most terminals that I know of, and, perhaps a very good thing. Additionally, you can use <code>alt</code> or <code>shift</code> alongside an arrow key to move by words or words (without considering punctuation) respectively.</p> <p>You can also use the right arrow key to accept a suggestion just as you can with <code>tab</code>. If a command is outlined, simply pressing the right arrow (or <code>Ctrl+e</code> as we will see shortly) is enough to materialize it.</p> <script src="https://asciinema.org/a/t33sQwpuL1hs1OQ9QF56rPudz.js" id="asciicast-t33sQwpuL1hs1OQ9QF56rPudz" async="true"></script> <p>As you can see, first I start typing <code>clang</code>, then hit the right arrow to materialize it. After that, I use just the arrow keys to move back and forth. Using <code>alt</code> allows me to move by word, and using shift right after allows me to skip punctuation. If you’re clever, you might notice that <code>alt</code> considers the <code>--</code> in <code>--help</code> to be its own word, whereas <code>shift</code> does not.</p> <h2 id="more-pieces-of-navigation">more pieces of navigation</h2> <p>If you’ve ever used vanilla Emacs, you will know that Emacs has a somewhat strange approach to keybindings. It’s not that <code>vi</code> (or <code>vim</code> or <code>nvim</code>) is necessarily intuitive, but the whole notion of moving around while holding <code>Ctrl</code> is kind of hilarious to me. For example, left or right are <code>ctrl+b</code> and <code>ctrl+f</code> respectively.</p> <p>Why, you say?</p> <p>Ah, yeah, not the slightest idea.</p> <p>I assume it seemed reasonable to someone? I’m not even sure why you wouldn’t just co-opt the <code>vim</code> style <code>hjkl</code> or even <code>jkl;</code> to at least keep your fingers in the same place during typing.</p> <p>Anyways, <code>fish</code> loves Emacs style bindings so much that you can use all the classic ones.</p> <p>There are only a few I think are worth talking about though, because they can be rather handy, namely <code>ctrl-a</code> (which goes to the front of the line) and <code>ctrl-e</code> (which, surprise, goes to the end of the line).</p> <p>There are also oddballs, like <code>ctrl-t</code> to transpose characters, <code>alt-t</code> to transpose words, <code>alt-c</code> to capitalize the latest word, <code>alt-u</code> to make the latest word all caps. (ALL CAPS when you spell the man name.)</p> <p>I personally just re-type things, but maybe you’ll find use in it.</p> <h2 id="command-history">command history</h2> <p>Recently, I’ve embraced not typing the same stuff over and over. I like <code>history</code> (which just dumps the latest command history into <code>less</code> - or presumably whatever pager you’ve chosen). If you use Emacs bindings, then <code>ctrl-r</code> is especially good.</p> <p>Essentially, it let search through the history of your past commands with a decent fuzzy search. If you want to get a sample of what you’ve written, pressing <code>ctrl-r</code> while inside the search takes you to older records, whereas <code>ctrl-s</code> takes you to newer ones.</p> <h2 id="less-is-more"><em>less</em> is more</h2> <p><code>less</code> is a pager, which is a tool written for before the days of scrollable terminals. Essentially, it lets you use arrow keys or vim like bindings to look over a file or the output of a command. (Really just any stream of text.) You might balk at this given your fancy scrollable terminal, but consider the downside of the scrollable terminal: if you are like me, the outputs of your last commands are still in your “scrollback”, which can get you confused if you think they might be the output of your code after your latest compile &amp; run sequence.</p> <p><code>alt-p</code> lets you append <code>&amp;|</code> to a command, which lets you take both the <a rel="external" href="https://en.wikipedia.org/wiki/Standard_streams#Standard_output_.28stdout.29">standard output</a> and <a rel="external" href="https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr)">standard error</a> of a command and read it without worrying about mixing it up with the last output.</p> <script src="https://asciinema.org/a/lfVWNHUNYSS6WFyGC2fcj58Qx.js" id="asciicast-lfVWNHUNYSS6WFyGC2fcj58Qx" async="true"></script> <h2 id="tough-commands">tough commands</h2> <p>When your command gets too long you can use <code>alt-e</code> to open it in whatever you have declared as <code>EDITOR</code> or <code>VISUAL</code>. As a side note, you should certainly set these in whatever shell you’ve decided to choose.</p> <h2 id="the-duds">the duds</h2> <p>I could not, for the life of me, get <code>alt-w</code> to work quickly. Conceptually, you are supposed to It took probably 10 seconds, which is much slower than virtually everything else in my terminal emulator seems to operate at. I also suspect that just using <code>man</code> is a faster approach to getting the same conclusion.</p> <section class="footnotes"> <ol class="footnotes-list"> <li id="fn-disclaimer"> <p>I’m not actually terribly old - both in the cosmic sense and in the computing sense. In fact, I personally have only spanned 5 prime ministers, which is my favourite measure of time. As a result, I don’t have a lot of the historical context for why someone might choose shells like <code>tcsh</code> or <code>bash</code>. I’m sensitive to the concept that I might be doing a <a rel="external" href="https://www.youtube.com/watch?v=WhkX6jop9DQ">Chesterton’s Fence</a> with this one, but I’m open to hearing alternative opinions. My e-mail address <em>is</em> on the front page of this blog after all. <a href="#fr-disclaimer-1">↩</a></p> </li> <li id="fn-disclaimer2"> <p>I’m mostly focused on interactive usage here, which is most of what I use my shell for. After reading the piece of poetry that is <a rel="external" href="https://j3s.sh/thought/write-posix-shell.html">j3s’s <em>write posix shell</em></a>, I was to some extent convinced that using the most rock solid and well-specified. <a href="#fr-disclaimer2-1">↩</a></p> </li> </ol> </section> 2025-08-30T00:00:00+00:00 2025-08-30T00:00:00+00:00 Aiden Fox Ivey https://aidenfoxivey.com/posts/tinytapeout/ <p>On the encouragement of my friend <a rel="external" href="https://www.nanik.ca/">Nanik Adnani</a>, I participated in <a rel="external" href="https://tinytapeout.com/">Tiny Tapeout 7</a> not long ago. While I had written Verilog and VHDL (both languages for <em>hardware description</em>) for the purpose of making designs for an FPGA (often the <a rel="external" href="https://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&amp;No=1081">DE10 from terasIC</a>), I had never really dreamed of being able to design an ASIC.</p> <p>I participated in “shuttle” 7, which used the now defunct <a rel="external" href="https://efabless.com/">efabless</a> to actually create the chips.</p> <p><img src="/img/tt07.avif" alt="" /></p> <p>The board as shown here is actually one board stacked on another. The bottom one is the “carrier board”, which has connectors, switches, buttons, and a glorious 7-segment display. Atop it lives the <a rel="external" href="https://en.wikipedia.org/wiki/Flat_no-leads_package">QFN</a> (quad flat no-leads package), which is the little black square on top of the “daughterboard”.</p> <p>The actual chip lives inside the QFN (which is mostly a plastic shell and little leads).</p> <p>Moritz94 of Wikipedia provides this image (with attached <a rel="external" href="https://creativecommons.org/licenses/by-sa/3.0">license</a>) of the QFN internally.</p> <p><img src="/img/QFN_side_view.svg" alt="" /></p> <p>Inside the QFN is the chip, which is rendered here as such…</p> <p><img src="/img/tt07_render.png" alt="" /></p> <p>This shows the different layers of the chip inside, which is mostly made from elaborating the logic explained within the Verilog HDL I wrote into NAND gates, which are arranged out of transistors.</p> <p>Here’s a diagram that I made that shows how you can design a NAND gate using transistors (both PMOS and NMOS). The PMOS create a pull up network while the NMOS create a pull down network. A PMOS is noted via a circle at the gate terminal.</p> <p><img src="/img/nand_transistor.svg" alt="" /></p> <p>Vss is low voltage, whereas Vdd is high voltage. If either A or B is low, then Out is mapped to Vdd, if A and B are both high though, Out is mapped to Vss. This maps to a NAND gate, where only <code>(nand #t #t)</code> is <code>#f</code>, everything else being <code>#t</code>.</p> <blockquote> <p>Thanks to <a rel="external" href="https://github.com/kdp1965">kdp1965</a> from the Tiny Tapeout Discord for resurrecting my original Verilog code. I cannot quite recall how I originally deleted my submission, but I imagine that it had something to do with my propensity to try to migrate off of Github and fondness for scripts that carelessly invoke <a rel="external" href="https://cli.github.com/"><code>gh</code></a>.</p> </blockquote> <p>Reproduced below is my project.</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="verilog"><span class="giallo-l"><span style="color: light-dark(#6A737D, #6A737D);">/*</span></span> <span class="giallo-l"><span style="color: light-dark(#6A737D, #6A737D);">* Copyright (c) 2024 Aiden Fox Ivey</span></span> <span class="giallo-l"><span style="color: light-dark(#6A737D, #6A737D);">* SPDX-License-Identifier: Apache-2.0</span></span> <span class="giallo-l"><span style="color: light-dark(#6A737D, #6A737D);">*/</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">`default_nettype</span><span> none</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">module</span><span style="color: light-dark(#6F42C1, #B392F0);"> tt_um_aidenfoxivey</span><span> (</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ui_in, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> Dedicated inputs</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> output</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] uo_out, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> Dedicated outputs</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] uio_in, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> IOs: Input path</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> output</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] uio_out, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> IOs: Output path</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> output</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] uio_oe, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> IOs: Enable path (active high: 0=input, 1=output)</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> ena, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> always 1 when the design is powered, so you can ignore it</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> clk, </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> clock</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> rst_n </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> reset_n - low to reset</span></span> <span class="giallo-l"><span>);</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> assign</span><span> uio_out </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> assign</span><span> uio_oe </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#22863A, #85E89D);"> crc8</span><span style="color: light-dark(#22863A, #85E89D);"> crc</span><span> (</span></span> <span class="giallo-l"><span> .data_in(ui_in),</span></span> <span class="giallo-l"><span> .data_out(uo_out),</span></span> <span class="giallo-l"><span> .rst(!rst_n),</span></span> <span class="giallo-l"><span> .clk(clk),</span></span> <span class="giallo-l"><span> .enable(uio_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>])</span></span> <span class="giallo-l"><span> )</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">endmodule</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> 1+x^1+x^2+x^8;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">module</span><span style="color: light-dark(#6F42C1, #B392F0);"> crc8</span><span> (</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] data_in,</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> output</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] data_out,</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> rst,</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> clk,</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> input</span><span style="color: light-dark(#D73A49, #F97583);"> wire</span><span> enable</span></span> <span class="giallo-l"><span>);</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">reg</span><span> [</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>:</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] next_crc, curr_crc;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">assign</span><span> data_out </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">always</span><span> @(</span><span style="color: light-dark(#D73A49, #F97583);">posedge</span><span> clk </span><span style="color: light-dark(#D73A49, #F97583);">or</span><span style="color: light-dark(#D73A49, #F97583);"> posedge</span><span> rst) </span><span style="color: light-dark(#D73A49, #F97583);">begin</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> if</span><span> (rst) </span><span style="color: light-dark(#D73A49, #F97583);">begin</span></span> <span class="giallo-l"><span> curr_crc </span><span style="color: light-dark(#D73A49, #F97583);">&lt;=</span><span> {</span><span style="color: light-dark(#005CC5, #79B8FF);">8</span><span>{</span><span style="color: light-dark(#005CC5, #79B8FF);">1&#39;b0</span><span>}}; </span><span style="color: light-dark(#6A737D, #6A737D);">//</span><span style="color: light-dark(#6A737D, #6A737D);"> CCITT initial value is defined as 0</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> end</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> else</span><span style="color: light-dark(#D73A49, #F97583);"> begin</span></span> <span class="giallo-l"><span> curr_crc </span><span style="color: light-dark(#D73A49, #F97583);">&lt;=</span><span> enable ? next_crc : curr_crc;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> end</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">end</span><span style="color: light-dark(#6A737D, #6A737D);"> //</span><span style="color: light-dark(#6A737D, #6A737D);"> always</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">always</span><span> @(</span><span style="color: light-dark(#D73A49, #F97583);">*</span><span>) </span><span style="color: light-dark(#D73A49, #F97583);">begin</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">3</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">4</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>];</span></span> <span class="giallo-l"><span> next_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>] </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ curr_crc[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">5</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">6</span><span>] ^ data_in[</span><span style="color: light-dark(#005CC5, #79B8FF);">7</span><span>];</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">end</span><span style="color: light-dark(#6A737D, #6A737D);"> //</span><span style="color: light-dark(#6A737D, #6A737D);"> always</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">endmodule</span><span style="color: light-dark(#6A737D, #6A737D);"> //</span><span style="color: light-dark(#6A737D, #6A737D);"> crc8</span></span></code></pre> <p>As you can see, it is <em>extremely</em> simple. I was mostly eager to get a design taped out and also left this project for one weekend. (Don’t be like me - plan out your projects and work in small chunks if you have the option / ability.)</p> <p>I think I also wrote a test for my submission, but that <a rel="external" href="https://www.cocotb.org/">cocotb</a> code is now missing in action.</p> <p>The actual gist of my project is a very simple hardware implementation of a cyclic redundancy check that produces 8-bit values following the CCITT standard. CCITT here being the <em>Comité Consultatif International Téléphonique et Télégraphique</em>, which is the old name of the <a rel="external" href="https://en.wikipedia.org/wiki/ITU-T">ITU-T</a>.</p> <p>Essentially, this CRC-8 implementation is used for telecommunications! I picked it because… actually I’ll be honest, I have no idea why I picked it. I never wrote that part down.</p> <p>A brief explanation of the cyclic redundancy check is that it is a method that can be used to correct errors when data is sent over a medium.</p> <p>Before we proceed, say this with me: <strong>CRCs are not substitutes for digital signatures or message authentication codes</strong>.</p> <p>Basically, don’t use a CRC and expect your scheme to be resistant towards intentional modification. CRCs do not provide authentication.</p> <p>Essentially, the approach for calculating the CRC of some specific value requires dividing the padded binary value by a divisor that is specified for each specific standard of CRC. The remainder of this division is then divided itself repeatedly, until the dividend is equal to 0. The remainder value is returned.</p> <p>If the value isn’t modified in transit, then dividing the returned value by the remainder value from the first part should yield all zeroes for a dividend and all zeroes for a remainder. Otherwise, there was a bit error.</p> <p>The <a rel="external" href="https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Mathematics">Wikipedia page for CRCs</a> has a good summary on <em>why</em> this works, as well as a more precise description of how it works than what I offered.</p> <p>For CRC-8 CCITT, using a <a rel="external" href="https://crccalc.com/?crc=FA&amp;method=CRC-8&amp;datatype=ascii&amp;outtype=hex">handy calculator</a> will tell you that the value of 0xAF corresponds to a value of 0x44.</p> <script src="https://asciinema.org/a/ShslHnaHVBdb5eQcyzuPj4WZE.js" id="asciicast-ShslHnaHVBdb5eQcyzuPj4WZE" async="true"></script> <p>It works!! You can read more about the specific project <a rel="external" href="https://tinytapeout.com/chips/tt07/tt_um_aidenfoxivey">here</a>.</p> <p>In the future I’d really like to try implementing some subset of the RISC-V standard.</p> <p>That’s all for now though. :)</p> 2025-08-28T00:00:00+00:00 2025-08-28T00:00:00+00:00 Aiden Fox Ivey https://aidenfoxivey.com/posts/ffi/ <p>To begin this blog post, I see it as most fitting to place a definition. The reasoning behind which I will elaborate upon shortly.</p> <p><strong>Linguae Francae</strong>: A common language used by people of diverse backgrounds to communicate with one another, often a basic form of speech with simplified grammar, particularly, one that is not the first language of any of its speakers.</p> <p>In the context of modern computers, it is hard to imagine any programming language as more fitting for the title of <em>linguae francae</em> than the C programming language.</p> <p>I will elaborate on this point, however I first need to provide some context as to the history of C and justification for still using it.</p> <p>To some extent, C’s popularity can be credited with Dennis Ritchie (the creator of C) reimplementing the kernel of Research Unix in C. It is also likely a byproduct of the GNU userspace, the Linux kernel, and common runtimes for languages such as Ruby or Python being implemented in C.</p> <p>It’s also worth mentioning that virtually all modern operating systems define their interfaces in terms of C’s abstract model. Between this fact and a faulty understanding of how modern computers work, this is how people casually <a rel="external" href="https://queue.acm.org/detail.cfm?id=3212479">assume that C is a low level language</a>.</p> <p>The result of this choice of that when a non trivial program is to be run in a language other than C, there must be some connection with C code at some point down the line.</p> <p>A secondary reason to want to interface with C is that a large number of the most widely useful (or hard to replace) libraries are written in C.</p> <p><a rel="external" href="https://curl.se/libcurl/">libcurl</a>, <a rel="external" href="https://openssl-library.org/">openssl</a>, and <a rel="external" href="https://zlib.net/">zlib</a> are all great examples of this. Respectively, they provide a way to interact with network protocols, use cryptographic algorithms, or compress data. Since the time and effort to make sure that these implementations are correct and efficient is <strong>immense</strong>, it would suit a clever software engineer well to reuse these libraries.</p> <p>If you’ve ever worked with a library in C before, you can probably get the gist of how someone might use a big C library like this within C code. (Don’t worry if you haven’t. Just know that it implies using <code>#include</code> and then adding a flag when you compile it.)</p> <p>However, this doesn’t leave much room for programmers who want to use a language other than C. This is where the namesake of this blog post comes in. The <em>foreign function interface</em> is the idea of making an interface between different programming languages. Usually the term implicitly describes interfacing a given language with the C programming language, although this is not <em>necessary</em> for the definition.</p> <p>(In this article, I will use FFI as shorthand to refer to some general foreign function interface between a given language and C.)</p> <h2 id="a-quick-example">A quick example</h2> <p>First, let’s write a simple definition for some code that calculates the nth value of the Fibonacci sequence.</p> <p>The crux of a Fibonacci sequence is that a given Fibonacci number is defined as the sum of the two Fibonacci numbers before it. As a result, it lends itself to be written recursively. We will write it instead, imperatively. In the spirit of neuroticism, we will first figure out what the most appropriate C language data type is to store the loop counter. Normal people might opt to use the integer data type, but we will consider this more carefully. (Do not do this when you are programming normally. It is an anti-pattern.)</p> <p>On my platform, <code>unsigned long long</code> has a max size of 2^64 - 1. Let’s determine the largest Fibonacci number that fits in a 64-bit integer. I’ll use <a rel="external" href="https://www.sagemath.org/">SageMath</a> for this. (SageMath is kind of confusing - it’s like a mathematics system that integrates lots of open source libraries with a language that is essentially a modified form of Python.)</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="python"><span class="giallo-l"><span>limit</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span style="color: light-dark(#005CC5, #79B8FF);"> 2</span><span style="color: light-dark(#D73A49, #F97583);">^</span><span style="color: light-dark(#005CC5, #79B8FF);">64</span><span style="color: light-dark(#D73A49, #F97583);"> -</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span></span> <span class="giallo-l"><span>x</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">while</span><span> fibonacci</span><span>(</span><span>x</span><span>)</span><span style="color: light-dark(#D73A49, #F97583);"> &lt;=</span><span> limit</span><span>:</span></span> <span class="giallo-l"><span> x</span><span style="color: light-dark(#D73A49, #F97583);"> +=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span></span> <span class="giallo-l"><span style="color: light-dark(#005CC5, #79B8FF);">print</span><span>(</span><span>x</span><span style="color: light-dark(#D73A49, #F97583);"> -</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span><span>)</span></span></code></pre> <p>This prints <code>93</code>, which means that the 93rd Fibonacci number is the largest number we can store within our 64-bit unsigned integer. Thus, we can use a <code>char</code> to store our loop counter variable. This is because the max size of the signed char, which is the default when not specified as unsigned or signed, is 127.</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="c"><span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#E36209, #FFAB70);"> n</span><span>)</span><span> {</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> char</span><span> i </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span> a </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>,</span><span> b </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span><span>,</span><span> tmp</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> for</span><span> (</span><span>;</span><span> i </span><span style="color: light-dark(#D73A49, #F97583);">&lt;</span><span> n</span><span>;</span><span> i</span><span style="color: light-dark(#D73A49, #F97583);">++</span><span>)</span><span> {</span></span> <span class="giallo-l"><span> tmp </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> a</span><span>;</span></span> <span class="giallo-l"><span> a </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> b</span><span>;</span></span> <span class="giallo-l"><span> b </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> tmp </span><span style="color: light-dark(#D73A49, #F97583);">+</span><span> b</span><span>;</span></span> <span class="giallo-l"><span> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span> a</span><span>;</span></span> <span class="giallo-l"><span>}</span></span></code></pre><h2 id="a-foray-into-compilers">A foray into compilers</h2> <p>Normally, as I mentioned before, Fibonacci would be recursively defined, but this makes more sense in functional languages like <a rel="external" href="https://www.haskell.org/">Haskell</a> where their compilers are written to rewrite recursive definitions into imperative code. In a language where the compilers lack this feature, this code example would incur unnecessary stack frames while executing.</p> <p>Consider this recursive definition.</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="c"><span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#E36209, #FFAB70);"> n</span><span>)</span><span> {</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> if</span><span> (</span><span>n </span><span style="color: light-dark(#D73A49, #F97583);">==</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span style="color: light-dark(#D73A49, #F97583);"> ||</span><span> n </span><span style="color: light-dark(#D73A49, #F97583);">==</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span><span>)</span><span> {</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span> n</span><span>;</span></span> <span class="giallo-l"><span> }</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span>n </span><span style="color: light-dark(#D73A49, #F97583);">-</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span><span>)</span><span style="color: light-dark(#D73A49, #F97583);"> +</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span>n </span><span style="color: light-dark(#D73A49, #F97583);">-</span><span style="color: light-dark(#005CC5, #79B8FF);"> 2</span><span>)</span><span>;</span></span> <span class="giallo-l"><span>}</span></span></code></pre> <p>After running <code>clang -S -O3 recursive_fib.c</code>, we are treated with the following (slightly cleaned up) ARM64 assembly code.</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="asm"><span class="giallo-l"><span style="color: light-dark(#6F42C1, #B392F0);">fibonacci</span><span style="color: light-dark(#6F42C1, #B392F0);">:</span></span> <span class="giallo-l"><span> stp x20, x19, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>, #-</span><span style="color: light-dark(#005CC5, #79B8FF);">32</span><span>]!</span></span> <span class="giallo-l"><span> stp x29, x30, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>, #</span><span style="color: light-dark(#005CC5, #79B8FF);">16</span><span>]</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> add</span><span> x29, </span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>, #</span><span style="color: light-dark(#005CC5, #79B8FF);">16</span></span> <span class="giallo-l"><span> .cfi_def_cfa w29, </span><span style="color: light-dark(#005CC5, #79B8FF);">16</span></span> <span class="giallo-l"><span> .cfi_offset w30, -</span><span style="color: light-dark(#005CC5, #79B8FF);">8</span></span> <span class="giallo-l"><span> .cfi_offset w29, -</span><span style="color: light-dark(#005CC5, #79B8FF);">16</span></span> <span class="giallo-l"><span> .cfi_offset w19, -</span><span style="color: light-dark(#005CC5, #79B8FF);">24</span></span> <span class="giallo-l"><span> .cfi_offset w20, -</span><span style="color: light-dark(#005CC5, #79B8FF);">32</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> mov</span><span> x19, x0</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> cmp</span><span> x0, #</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span></span> <span class="giallo-l"><span> b.hs LBB0_2</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> mov</span><span> x20, #</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> add</span><span> x0, x19, x20</span></span> <span class="giallo-l"><span> ldp x29, x30, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>, #</span><span style="color: light-dark(#005CC5, #79B8FF);">16</span><span>]</span></span> <span class="giallo-l"><span> ldp x20, x19, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>], #</span><span style="color: light-dark(#005CC5, #79B8FF);">32</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> ret</span></span> <span class="giallo-l"><span style="color: light-dark(#6F42C1, #B392F0);">LBB0_2</span><span style="color: light-dark(#6F42C1, #B392F0);">:</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> mov</span><span> x20, #</span><span style="color: light-dark(#005CC5, #79B8FF);">0</span></span> <span class="giallo-l"><span style="color: light-dark(#6F42C1, #B392F0);">LBB0_3</span><span style="color: light-dark(#6F42C1, #B392F0);">:</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> sub</span><span> x0, x19, #</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span></span> <span class="giallo-l"><span style="color: light-dark(#005CC5, #79B8FF);"> bl</span><span> fibonacci</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> sub</span><span> x19, x19, #</span><span style="color: light-dark(#005CC5, #79B8FF);">2</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> add</span><span> x20, x0, x20</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> cmp</span><span> x19, #</span><span style="color: light-dark(#005CC5, #79B8FF);">1</span></span> <span class="giallo-l"><span> b.hi LBB0_3</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> add</span><span> x0, x19, x20</span></span> <span class="giallo-l"><span> ldp x29, x30, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>, #</span><span style="color: light-dark(#005CC5, #79B8FF);">16</span><span>]</span></span> <span class="giallo-l"><span> ldp x20, x19, [</span><span style="color: light-dark(#005CC5, #79B8FF);">sp</span><span>], #</span><span style="color: light-dark(#005CC5, #79B8FF);">32</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> ret</span></span></code></pre> <p>First, the code moves the argument register <code>x0</code> to <code>x19</code> to save it and restore before returning. <code>cmp x0, #2</code> coupled with <code>b.hs</code> jumps to the label <code>LBB0_2</code> if the value is greater than or equal to 2. Otherwise, we just return the value of the argument that was held in <code>x0</code>. In the other case, we calculate <code>fibonacci(n-1)</code>, and then sum it, checking for when we reach the <code>n == 1 || n == 0</code> case.</p> <p>Interestingly, the compiler has outwitted us here, seeing as though we expected that we would get a naive implementation that called the Fibonacci sequence twice recursively rather than once recursively within a loop.</p> <p>This is certainly better than what we forecast, but still not optimal, given that a truly optimized iterative solution would just use a single loop without any recursion and, as a result, any additional stack frames.</p> <p>We can now dispel this temporary foray into compiler optimization and head back to the land of foreign function interfaces.</p> <h2 id="back-on-track">Back on track</h2> <p>Let’s take the iterative example I wrote and turn it into a shared object. In order to do this, I run <code>clang -shared -o libfibonacci.so -fPIC fib.c</code>.</p> <p>A shared object (<code>.so</code>) is a kind of object file that can be loaded into a program at runtime rather than at compile time. In order to use our Fibonacci implementation inside Python code, we must write it in the form of a shared object, since the Python implementation will load it at runtime and Python does not have a separate compilation step in the same sense as C.</p> <p>Notably, we do have to either output an object file or a shared object file here, because the file we wrote earlier does not have a main function. As a result, trying to turn it into an executable will fail, since there is no place for code execution to start from.</p> <p>On more esoteric targets like microcontrollers, frequently one can specify the name of the entry point they would like to invoke rather than, on modern operating systems, which usually just assume “main” is the name of the entry point (at least during compilation).</p> <p>Also, note that we have the flag <code>-fPIC</code>. This means that any given code needs to be generated such that it <em>doesn’t</em> depend on being at a specific address to work. Instead, the code will opt to generate instructions that jump to offsets with respect to labels such that it can be mapped anywhere in memory.</p> <p>The last thing that might be worthwhile to mention is that if you are on a Mac and you’ve poked around the disk a lot, you may have noticed files called “dylib”. These are a more modern but still compatible form of the shared object that we referred to earlier. They’re commonly called dynamic libraries.</p> <p>Now let’s write a Python file that invokes the shared library we wrote and executes it:</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="python"><span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">import</span><span> ctypes</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">import</span><span> time</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">def</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span>n</span><span>)</span><span>:</span></span> <span class="giallo-l"><span> i</span><span>,</span><span> a</span><span>,</span><span> b</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>,</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>,</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> while</span><span> i</span><span style="color: light-dark(#D73A49, #F97583);"> &lt;</span><span> n</span><span>:</span></span> <span class="giallo-l"><span> a</span><span>,</span><span> b</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> b</span><span>,</span><span> a</span><span style="color: light-dark(#D73A49, #F97583);"> +</span><span> b</span></span> <span class="giallo-l"><span> i</span><span style="color: light-dark(#D73A49, #F97583);"> +=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span> a</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">def</span><span style="color: light-dark(#6F42C1, #B392F0);"> main</span><span>(</span><span>)</span><span>:</span></span> <span class="giallo-l"><span> lib</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> ctypes</span><span>.</span><span>CDLL</span><span>(</span><span style="color: light-dark(#032F62, #9ECBFF);">&#39;</span><span style="color: light-dark(#032F62, #9ECBFF);">./libfibonacci.so</span><span style="color: light-dark(#032F62, #9ECBFF);">&#39;</span><span>)</span></span> <span class="giallo-l"><span> lib</span><span>.</span><span>fibonacci</span><span>.</span><span>argtypes</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> [</span><span>ctypes</span><span>.</span><span>c_ulonglong</span><span>]</span></span> <span class="giallo-l"><span> lib</span><span>.</span><span>fibonacci</span><span>.</span><span>restype</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> ctypes</span><span>.</span><span>c_ulonglong</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span> python_start</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> time</span><span>.</span><span>time</span><span>(</span><span>)</span></span> <span class="giallo-l"><span> python_result</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> fibonacci</span><span>(</span><span style="color: light-dark(#005CC5, #79B8FF);">93</span><span>)</span></span> <span class="giallo-l"><span> python_duration</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> time</span><span>.</span><span>time</span><span>(</span><span>)</span><span style="color: light-dark(#D73A49, #F97583);"> -</span><span> python_start</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span> c_start</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> time</span><span>.</span><span>time</span><span>(</span><span>)</span></span> <span class="giallo-l"><span> c_result</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> lib</span><span>.</span><span>fibonacci</span><span>(</span><span style="color: light-dark(#005CC5, #79B8FF);">93</span><span>)</span></span> <span class="giallo-l"><span> c_duration</span><span style="color: light-dark(#D73A49, #F97583);"> =</span><span> time</span><span>.</span><span>time</span><span>(</span><span>)</span><span style="color: light-dark(#D73A49, #F97583);"> -</span><span> c_start</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#005CC5, #79B8FF);"> print</span><span>(</span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span style="color: light-dark(#032F62, #9ECBFF);">In C: </span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span>,</span><span> c_result</span><span>,</span><span> c_duration</span><span>)</span></span> <span class="giallo-l"><span style="color: light-dark(#005CC5, #79B8FF);"> print</span><span>(</span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span style="color: light-dark(#032F62, #9ECBFF);">In Python: </span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span>,</span><span> python_result</span><span>,</span><span> python_duration</span><span>)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span>main</span><span>(</span><span>)</span></span></code></pre> <p>We find that both solutions are the identical value of 12200160415121876738, with the C implementation taking <code>3.10e-06</code> seconds and the Python implementation taking <code>5.96e-06</code> seconds.</p> <p>We are now calling into C from Python! If you’ve been following along, you can safely say that you’ve used a foreign function interface.</p> <p>One point of curiosity, though, is that the C code (when run through the FFI) is not an order of magnitude faster than the Python implementation.</p> <p>Let’s then see how long this given code takes to run without using the foreign function interface by adapting our C code into its own standalone executable.</p> <pre class="giallo" style="color-scheme: light dark; color: light-dark(#24292E, #E1E4E8); background-color: light-dark(#FFFFFF, #24292E);"><code data-lang="c"><span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">#</span><span style="color: light-dark(#D73A49, #F97583);">include</span><span style="color: light-dark(#032F62, #9ECBFF);"> &lt;</span><span style="color: light-dark(#032F62, #9ECBFF);">stdio.h</span><span style="color: light-dark(#032F62, #9ECBFF);">&gt;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">#</span><span style="color: light-dark(#D73A49, #F97583);">include</span><span style="color: light-dark(#032F62, #9ECBFF);"> &lt;</span><span style="color: light-dark(#032F62, #9ECBFF);">time.h</span><span style="color: light-dark(#032F62, #9ECBFF);">&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span style="color: light-dark(#D73A49, #F97583);">unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#E36209, #FFAB70);"> n</span><span>)</span><span> {</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> char</span><span> i </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span> a </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>,</span><span> b </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#005CC5, #79B8FF);"> 1</span><span>,</span><span> tmp</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> for</span><span> (</span><span>;</span><span> i </span><span style="color: light-dark(#D73A49, #F97583);">&lt;</span><span> n</span><span>;</span><span> i</span><span style="color: light-dark(#D73A49, #F97583);">++</span><span>)</span><span> {</span></span> <span class="giallo-l"><span> tmp </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> a</span><span>;</span></span> <span class="giallo-l"><span> a </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> b</span><span>;</span></span> <span class="giallo-l"><span> b </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> tmp </span><span style="color: light-dark(#D73A49, #F97583);">+</span><span> b</span><span>;</span></span> <span class="giallo-l"><span> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span> a</span><span>;</span></span> <span class="giallo-l"><span>}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);">int</span><span style="color: light-dark(#6F42C1, #B392F0);"> main</span><span>(</span><span style="color: light-dark(#D73A49, #F97583);">void</span><span>)</span><span> {</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> time_t</span><span> start</span><span>,</span><span> end</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> double</span><span> cpu_time_used</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> unsigned</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span style="color: light-dark(#D73A49, #F97583);"> long</span><span> result</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span> start </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#6F42C1, #B392F0);"> clock</span><span>(</span><span>)</span><span>;</span></span> <span class="giallo-l"><span> result </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#6F42C1, #B392F0);"> fibonacci</span><span>(</span><span style="color: light-dark(#005CC5, #79B8FF);">93</span><span>)</span><span>;</span></span> <span class="giallo-l"><span> end </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span style="color: light-dark(#6F42C1, #B392F0);"> clock</span><span>(</span><span>)</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span> cpu_time_used </span><span style="color: light-dark(#D73A49, #F97583);">=</span><span> (</span><span>(</span><span style="color: light-dark(#D73A49, #F97583);">double</span><span>)</span><span>(</span><span>end </span><span style="color: light-dark(#D73A49, #F97583);">-</span><span> start</span><span>)</span><span>)</span><span style="color: light-dark(#D73A49, #F97583);"> /</span><span> CLOCKS_PER_SEC</span><span>;</span></span> <span class="giallo-l"><span style="color: light-dark(#6F42C1, #B392F0);"> printf</span><span>(</span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span style="color: light-dark(#005CC5, #79B8FF);">%llu</span><span style="color: light-dark(#032F62, #9ECBFF);"> which took </span><span style="color: light-dark(#005CC5, #79B8FF);">%e</span><span style="color: light-dark(#005CC5, #79B8FF);">\n</span><span style="color: light-dark(#032F62, #9ECBFF);">&quot;</span><span>,</span><span> result</span><span>,</span><span> cpu_time_used</span><span>)</span><span>;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span style="color: light-dark(#D73A49, #F97583);"> return</span><span style="color: light-dark(#005CC5, #79B8FF);"> 0</span><span>;</span></span> <span class="giallo-l"><span>}</span></span></code></pre> <p>On my machine, this took somewhere around <code>1.50e-06</code> seconds to execute, which is notably less than the C code running through the foreign function interface.</p>