SIMD in JavaScript via C++ and Emscripten

Emscripten, Mozilla’s C/C++ to JavaScript compiler, can be used to port existing native C/C++ applications to the Web platform. When paired with a fast JavaScript engine, the applications run at near-native speeds. However, compute intensive C/C++ applications, such as games and media-processing, making use of SIMD intrinsics or gcc style vector code cannot achieve near-native speed, because JavaScript does not have language support for expressing SIMD operations. This paper presents SIMD.JS, an evolving new JavaScript standard, enabling SIMD operations at the JavaScript language level, and extensions to Emscripten, enabling compilation of C++ programs that make use of SIMD intrinsics or gcc style vector code. An extensive subset of available C++ SIMD x86 intrinsics is supported. Using Emscripten, we show how C/C++ SIMD programs are compiled into JavaScript resulting in equivalent speedups compared to scalar code. The new powerful combination of SIMD.JS enabled JavaScript engines and Emscripten’s newly added ability to utilize the SIMD.JS primitives for it’s code generation will allow a new set of compute intensive C/C++ applications to be ported to the Web platform, thereby enabling the next leap in performance on the web platform.