https://semikolan.me/tags/cpu/ Recent content in cpu on semikolan Hugo en Mon, 27 Jul 2026 21:19:11 +0530 https://semikolan.me/blog/quiet-cost-of-a-fast-loop/ Tue, 30 Jun 2026 00:00:00 +0000 https://semikolan.me/blog/quiet-cost-of-a-fast-loop/ <p>The first time I saw a sorted array process faster than an identical unsorted one, I assumed I&rsquo;d measured wrong. Same data, same instructions, same count. The only difference was order — and order, I&rsquo;d been taught, doesn&rsquo;t change complexity.</p> <p>It doesn&rsquo;t. It changes the <em>constant</em>, and the constant is a physical thing living in the branch predictor.</p> <h2 id="the-branch-that-couldnt-guess">The branch that couldn&rsquo;t guess <a class="anchor" href="#the-branch-that-couldnt-guess" aria-label="Link to this section">#</a></h2> <p>A modern CPU runs ahead of itself. When it hits an <code>if</code>, it doesn&rsquo;t wait to learn the answer — it bets, and speculatively executes the branch it thinks you&rsquo;ll take. Guess right and the work is already done. Guess wrong and it throws away a dozen in-flight instructions and starts over.</p>