improve performance by using lookup tables (#4)

README.md

@@ -6,7 +6,7 @@
 > Fast & tiny [Wolt BlurHash](https://github.com/woltapp/blurhash) decoder implementation
 
 - 🤏 **Tiny**: ≈1kb minified
-- 🚀 **Fast**: up to 50% faster then [original `blurhash.decode`](https://github.com/woltapp/blurhash/tree/master/TypeScript#decodeblurhash-string-width-number-height-number-punch-number--uint8clampedarray) (see [benchmark](./benchmark.js))
+- 🚀 **Fast**: up to 70% faster then [original `blurhash.decode`](https://github.com/woltapp/blurhash/tree/master/TypeScript#decodeblurhash-string-width-number-height-number-punch-number--uint8clampedarray) (see [benchmark](./benchmark.js))
 
 [Demo](https://mad-gooze.github.io/fast-blurhash/)
 

index.js

@@ -1,10 +1,16 @@
-const digit =
- '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~';
+const digitLookup = new Uint8Array(128);
+for (let i = 0; i < 83; i++) {
+ digitLookup[
+ '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~'.charCodeAt(
+ i,
+ )
+ ] = i;
+}
 const decode83 = (str, start, end) => {
  let value = 0;
  while (start < end) {
  value *= 83;
- value += digit.indexOf(str[start++]);
+ value += digitLookup[str.charCodeAt(start++)];
  }
  return value;
 };
@@ -71,8 +77,6 @@ export function decodeBlurHash(blurHash, width, height, punch) {
  basisY = 0,
  colorIndex = 0,
  pixelIndex = 0,
- yh = 0,
- xw = 0,
  value = 0;
 
  const maximumValue = ((decode83(blurHash, 1, 2) + 1) / 13446) * (punch | 1);
@@ -86,26 +90,34 @@ export function decodeBlurHash(blurHash, width, height, punch) {
 
  for (i = 1; i < size; i++) {
  value = decode83(blurHash, 4 + i * 2, 6 + i * 2);
- colors[i * 3] = signSqr(~~(value / (19 * 19)) - 9) * maximumValue;
+ colors[i * 3] = signSqr(~~(value / 361) - 9) * maximumValue;
  colors[i * 3 + 1] = signSqr((~~(value / 19) % 19) - 9) * maximumValue;
  colors[i * 3 + 2] = signSqr((value % 19) - 9) * maximumValue;
  }
 
+ const cosinesY = new Float64Array(numY * height);
+ const cosinesX = new Float64Array(numX * width);
+ for (j = 0; j < numY; j++) {
+ for (y = 0; y < height; y++) {
+ cosinesY[j * height + y] = fastCos((PI * y * j) / height);
+ }
+ }
+ for (i = 0; i < numX; i++) {
+ for (x = 0; x < width; x++) {
+ cosinesX[i * width + x] = fastCos((PI * x * i) / width);
+ }
+ }
+
  const bytesPerRow = width * 4;
  const pixels = new Uint8ClampedArray(bytesPerRow * height);
 
  for (y = 0; y < height; y++) {
- yh = (PI * y) / height;
  for (x = 0; x < width; x++) {
- r = 0;
- g = 0;
- b = 0;
- xw = (PI * x) / width;
-
+ r = g = b = 0;
  for (j = 0; j < numY; j++) {
- basisY = fastCos(yh * j);
+ basisY = cosinesY[j * height + y];
  for (i = 0; i < numX; i++) {
- basis = fastCos(xw * i) * basisY;
+ basis = cosinesX[i * width + x] * basisY;
  colorIndex = (i + j * numX) * 3;
  r += colors[colorIndex] * basis;
  g += colors[colorIndex + 1] * basis;