Scan HTML even faster with SIMD instructions (C++ and C#) Earlier this year, both major Web engines (WebKit/Safari and Chromium/Chrome/Edge/Brave) accelerated HTML parsing using SIMD instructions. These ‘SIMD’ instructions are special instructions that are present in all our processors that can process multiple bytes at once (e.g., 16 bytes). The problem that WebKit and Chromium solve is to jump to the next target character as fast as possible: one of <, &, \r and \0. In C++, you can use std::find_first_of for this problem whereas in C#, you might use the SearchValues class. But we can do better with a bit of extra work. The WebKit and Chromium engineers use vectorized classification (Langdale and Lemire, 2019): we load blocks of bytes and identify the characters you seek using a few instructions. Then we identify the first such character loaded, if any. If no target character is found, we just move forward and load another block of characters. I reviewed the new methods from the Web engines in C++ and C# along with minor optimizations. The results are good, and it suggests that WebKit and Chromium engineers were right to adopt this optimization. But can we do better? Let us consider an example to see how the WebKit/Chromium approach works. Suppose that my HTML file is as follows: