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SIMD numeric type for EcmaScript
JavaScript HTML
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Latest commit a5529db Sep 7, 2018
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src Coerce load/store indexes with ToNumber. Mar 14, 2016
tc39 Remove stylesheet links Apr 25, 2017
LICENSE.txt Add zlib license to polyfill. Oct 18, 2013 Update Sep 7, 2018 Capitalize type names in Aug 4, 2015 Initial implementation + tests. Mar 31, 2013



SIMD.js has been taken out of active development in TC39 and removed from Stage 3, and is not being pursued by web browsers for implementation. SIMD operations exposed to the web are under active development within WebAssembly, with operations based on the SIMD.js operations. With WebAssembly in advanced development or shipping in multiple browsers, it seems like an adequate vehicle to subsume asm.js use cases, which are judged to be the broader cases. Although some developers have expressed interest in using SIMD.js outside of asm.js, implementers have found that implementing and optimizing for this case reliably creates a lot of complexity, and have made the decision to focus instead on delivering WebAssembly and SIMD instructions in WASM.

See for current development.

This repository retains a historical snapshot of the SIMD.js specification work:

  • The authoritative API reference documentation is generated from tc39/spec.html. You can view a rendered copy at .
  • A polyfill at src/ecmascript_simd.js, which can't implement value semantics, but includes a correct implementation of all functions
  • Extensive tests at src/ecmascript_simd_tests.js, which can be run using other files in src/. Benchmarks and example code live in the same directory.
  • A presentation explaining the motivation and outlining the approach at tc39/SIMD-128 TC-39.pdf
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