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Float16Array
A proposal to add float16 (aka half-precision or binary16) TypedArrays to JavaScript.
Status
Authors: Kevin Gibbons
Champions: Leo Balter, Kevin Gibbons
This proposal is at Stage 3 of The TC39 Process as of the May 2023 meeting. It awaits implementations.
Spec text is available here.
Implementations
This proposal is ready for engines to implement and ship. See this issue for current status of implementations.
Motivation
- Explicit request from the Color on the Web CG, for their use case with float-backed canvases.
- Useful for GPU operations, where full precision often isn't necessary and memory constraints are serious.
- WebGPU supports float16. It exposes/consumes raw ArrayBuffers. When those contain 32-bit floats, the pattern is to wrap the buffer in
new Float32Array(...); that doesn't work when they contain 16-bit floats. - Increasingly relevant with new tools like Stable Diffusion, where full-precision representations don't fit in VRAM on many machines.
- WebGPU supports float16. It exposes/consumes raw ArrayBuffers. When those contain 32-bit floats, the pattern is to wrap the buffer in
- WebGL/WebGL2 support float16.
- WebGL's
OES_texture_half_floatextension and WebGL2 support float16 texture, and also bothEXT_color_buffer_half_floatextensions support float16 render target. They expose/consume Uint16Arrays; that is not easy to handle.
- WebGL's
- ARM and IA-32 and Intel® 64 architectures support float16 intrinsics.
- In the C++23 specification,
std::float16_twill be supported to call the CPU instructions.
- In the C++23 specification,
- Faking it in userland has serious performance costs.
Proposal
This would add a new kind of TypedArray, Float16Array, to complement the existing Float32Array and Float64Array. It would also add two new methods on DataView for reading and setting float16 values, as getFloat16 and setFloat16, to complement the existing similar methods for working with full and double precision floats, as well as Math.f16round, to complement the existing Math.fround.
Userland
@petramoriken has a package implementing Float16Array which gets 100k+ downloads/week on npm. See that repository for examples of some of the limitations and downsides of trying to do this purely in userland - notably the impossibility of integrating correctly with other web platform features like WebGL's HALF_FLOAT buffers and structuredClone.