fft_webgpu.ts

/**
 * @license
 * Copyright 2022 Google LLC.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * =============================================================================
 */

import {getMainHeaderString as main, WebGPUProgram} from './webgpu_program';
import {computeDispatch, flatDispatchLayout} from './webgpu_util';

export class FFTProgram implements WebGPUProgram {
  variableNames: string[] = ['real', 'imag'];
  outputShape: number[] = [];
  shaderKey: string;
  dispatchLayout: {x: number[]};
  dispatch: [number, number, number];
  uniforms = 'exponentMultiplier : f32, denominator: f32,';
  workgroupSize: [number, number, number] = [64, 1, 1];
  size = true;
  component: string;

  constructor(component: 'real'|'imag', shape: [number, number]) {
    this.outputShape = shape;
    this.dispatchLayout = flatDispatchLayout(this.outputShape);
    this.dispatch = computeDispatch(
        this.dispatchLayout, this.outputShape, this.workgroupSize);

    this.component = component;
    this.shaderKey = `fft_${component}`;
  }

  getUserCode(): string {
    const opString = this.component === 'real' ?
        'return real * expR - imag * expI;' :
        'return real * expI + imag * expR;';
    const userCode = `
    fn unaryOpComplex(real: f32, expR: f32, imag: f32, expI: f32) -> f32 {
      ${opString}
    }

    fn mulMatDFT(batch: i32, index: i32) -> f32 {
      let indexRatio = f32(index) / f32(uniforms.realShape[1]);
      let exponentMultiplierTimesIndexRatio =
          uniforms.exponentMultiplier * indexRatio;

      var result = 0.0;

      for (var i = 0; i < uniforms.realShape[1]; i = i + 1) {
        // x = (-2|2 * PI / N) * index * i;
        let x = exponentMultiplierTimesIndexRatio * f32(i);
        let expR = cos(x);
        let expI = sin(x);
        let real = getReal(batch, i);
        let imag = getImag(batch, i);

        result = result +
            unaryOpComplex(real, expR, imag, expI) / uniforms.denominator;
      }

      return result;
    }

    ${main('index')} {
      if (index < uniforms.size) {
        let coords = getOutputCoords();
        setOutputAtIndex(index, mulMatDFT(coords[0], coords[1]));
      }
    }
  `;
    return userCode;
  }
}