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fp64arithmetic

The fp64arithmetic shader module provides the low-level double-single arithmetic used by fp64. Use it directly when you only need the arithmetic primitives and want to avoid including the full fp64 function library.

Uniforms​

{
  ONE: 'f32',
  SPLIT: 'f32'
}

These uniforms are supplied automatically by the module's defaultUniforms.

Usage​

import {fp64arithmetic} from '@luma.gl/shadertools';

const modules = [fp64arithmetic];

WGSL fp64u32 Subtraction​

WGSL also exposes:

fn sub_fp64u32_to_f32_bits(aBits: vec2u, bBits: vec2u) -> u32
fn sub_fp64u32_to_f32(aBits: vec2u, bBits: vec2u) -> f32

These helpers subtract two fp64u32 values, i.e. raw IEEE-754 binary64 values stored in vec2u, using integer arithmetic and round the exact result once to f32. They are intended for WebGPU paths that need f32(a64 - b64), rather than f32(a64) - f32(b64), without relying on emulated fp64 floating-point arithmetic.

A full bitwise drop-in implementation of fp64f32 arithmetic is intentionally not exposed. That approach is too expensive for iterative fragment shaders and can stress some GPU drivers.

aBits and bBits use canonical high/low word order:

  • .x is the high word containing sign, exponent, and high fraction bits
  • .y is the low 32 fraction bits

The existing high/low vec2f representation used by helpers like sub_fp64 is the fp64f32 representation.

If the source data comes from a JavaScript Float64Array reinterpreted as Uint32Array, convert from host word order before calling these helpers.

Remarks​

  • fp64 depends on fp64arithmetic, so applications that import fp64 do not usually need to add this module separately.
  • The helper uniforms are part of the module's implementation and should not normally need to be overridden by applications.