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updated murmerhash3_32_gc to slightly faster (15%) GTP-4 version #17

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updated murmerhash3_32_gc to slightly faster (15%) GTP-4 version #17

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74 changes: 36 additions & 38 deletions murmurhash3_gc.js
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
// thanks to GPT4 for this updated version which is about 15% faster, probably due to use of Math.imul

/**
* JS Implementation of MurmurHash3 (r136) (as of May 20, 2011)
*
Expand All @@ -11,54 +13,50 @@
* @return {number} 32-bit positive integer hash
*/

function murmurhash3_32_gc(key, seed) {
var remainder, bytes, h1, h1b, c1, c1b, c2, c2b, k1, i;

remainder = key.length & 3; // key.length % 4
bytes = key.length - remainder;
h1 = seed;
c1 = 0xcc9e2d51;
c2 = 0x1b873593;
i = 0;

while (i < bytes) {
k1 =
((key.charCodeAt(i) & 0xff)) |
((key.charCodeAt(++i) & 0xff) << 8) |
((key.charCodeAt(++i) & 0xff) << 16) |
((key.charCodeAt(++i) & 0xff) << 24);
++i;

k1 = ((((k1 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16))) & 0xffffffff;
function murmurhash3_32_gc(key, seed = 0) {
const c1 = 0xcc9e2d51;
const c2 = 0x1b873593;
let h1 = seed;
let roundedEnd = key.length & ~0x3;

for (let i = 0; i < roundedEnd; i += 4) {
let k1 =
(key.charCodeAt(i) & 0xff) |
((key.charCodeAt(i + 1) & 0xff) << 8) |
((key.charCodeAt(i + 2) & 0xff) << 16) |
((key.charCodeAt(i + 3) & 0xff) << 24);
k1 = Math.imul(k1, c1);
k1 = (k1 << 15) | (k1 >>> 17);
k1 = ((((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16))) & 0xffffffff;
k1 = Math.imul(k1, c2);

h1 ^= k1;
h1 = (h1 << 13) | (h1 >>> 19);
h1b = ((((h1 & 0xffff) * 5) + ((((h1 >>> 16) * 5) & 0xffff) << 16))) & 0xffffffff;
h1 = (((h1b & 0xffff) + 0x6b64) + ((((h1b >>> 16) + 0xe654) & 0xffff) << 16));
h1 = (h1 << 13) | (h1 >>> 19);
h1 = Math.imul(h1, 5) + 0xe6546b64;
}

let k1 = 0;
const val = key.length & 0x3;

if (val === 3) {
k1 = (key.charCodeAt(roundedEnd + 2) & 0xff) << 16;
}
if (val >= 2) {
k1 |= (key.charCodeAt(roundedEnd + 1) & 0xff) << 8;
}

k1 = 0;

switch (remainder) {
case 3: k1 ^= (key.charCodeAt(i + 2) & 0xff) << 16;
case 2: k1 ^= (key.charCodeAt(i + 1) & 0xff) << 8;
case 1: k1 ^= (key.charCodeAt(i) & 0xff);

k1 = (((k1 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16)) & 0xffffffff;
if (val >= 1) {
k1 |= key.charCodeAt(roundedEnd) & 0xff;
k1 = Math.imul(k1, c1);
k1 = (k1 << 15) | (k1 >>> 17);
k1 = (((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16)) & 0xffffffff;
k1 = Math.imul(k1, c2);
h1 ^= k1;
}

h1 ^= key.length;

h1 ^= key.length;
h1 ^= h1 >>> 16;
h1 = (((h1 & 0xffff) * 0x85ebca6b) + ((((h1 >>> 16) * 0x85ebca6b) & 0xffff) << 16)) & 0xffffffff;
h1 = Math.imul(h1, 0x85ebca6b);
h1 ^= h1 >>> 13;
h1 = ((((h1 & 0xffff) * 0xc2b2ae35) + ((((h1 >>> 16) * 0xc2b2ae35) & 0xffff) << 16))) & 0xffffffff;
h1 = Math.imul(h1, 0xc2b2ae35);
h1 ^= h1 >>> 16;

return h1 >>> 0;
}
}