Murmurhash160N

'use strict';

// Calculate N * 160 bits of hash value.
//   Based on murmurhash160 by bryc (github.com/bryc)
//   From: https://simonhf.wordpress.com/2010/09/25/murmurhash160/
function hash(key, bits=480) {

    let result = Buffer.alloc(bits / 8);

    for (let step = 0; step < bits / 160; ++step) {
        let k;
        const m1 = 1540483477, m2 = 433494437, m3 = 2971215073, m4 = 370248451, m5 = 1405695061;
        let h1 = key.length ^ step, h2 = h1 ^ m2, h3 = h1 ^ m3, h4 = h1 ^ m4, h5 = h1 ^ m5;

        let i, b;
        for (i = 0, b = key.length & -4; i < b; i += 4) {
            k = key[i + 3] << 24 | key[i + 2] << 16 | key[i + 1] << 8 | key[i];
            k = Math.imul(k, m1);
            k ^= k >>> 24;
            k = Math.imul(k, m1);

            h1 = Math.imul(h1, m1) ^ k ^ h2;
            h2 = Math.imul(h2, m2) ^ k ^ h3;
            h3 = Math.imul(h3, m3) ^ k ^ h4;
            h4 = Math.imul(h4, m4) ^ k ^ h5;
            h5 = Math.imul(h5, m5) ^ k ^ h1;
        }

        switch (key.length & 3) {
            case 3:
                h1 ^= key[i + 2] << 16;
                h2 ^= key[i + 2] << 16;
                h3 ^= key[i + 2] << 16;
                h4 ^= key[i + 2] << 16;
                h5 ^= key[i + 2] << 16;
            case 2:
                h1 ^= key[i + 1] << 8;
                h2 ^= key[i + 1] << 8;
                h3 ^= key[i + 1] << 8;
                h4 ^= key[i + 1] << 8;
                h5 ^= key[i + 1] << 8;
            case 1:
                h1 ^= key[i];
                h2 ^= key[i];
                h3 ^= key[i];
                h4 ^= key[i];
                h5 ^= key[i];
                h1 = Math.imul(h1, m1);
                h2 = Math.imul(h2, m2);
                h3 = Math.imul(h3, m3);
                h4 = Math.imul(h4, m4);
                h5 = Math.imul(h5, m5);
        }

        h1 ^= h1 >>> 13, h1 = Math.imul(h1, m1), h1 ^= h1 >>> 15;
        h2 ^= h2 >>> 13, h2 = Math.imul(h2, m2), h2 ^= h2 >>> 15;
        h3 ^= h3 >>> 13, h3 = Math.imul(h3, m3), h3 ^= h3 >>> 15;
        h4 ^= h4 >>> 13, h4 = Math.imul(h4, m4), h4 ^= h4 >>> 15;
        h5 ^= h5 >>> 13, h5 = Math.imul(h5, m5), h5 ^= h5 >>> 15;

        result.writeUInt32LE((h1 ^ h2 ^ h3 ^ h4 ^ h5) >>> 0, step * 20);
        result.writeUInt32LE((h2 ^ h1) >>> 0, step * 20 + 4);
        result.writeUInt32LE((h3 ^ h1) >>> 0, step * 20 + 8);
        result.writeUInt32LE((h4 ^ h1) >>> 0, step * 20 + 12);
        result.writeUInt32LE((h5 ^ h1) >>> 0, step * 20 + 16);
    }

    return result;
}

module.exports = hash;