thor-devkit
Version:
Typescript library to aid DApp development on VeChain Thor
65 lines • 4.25 kB
JavaScript
import { blake2b256 } from './blake2b';
import { Buffer } from 'buffer';
/**
* 2048 bits Bloom filter
*/
export class Bloom {
/** estimate k(number of hash functions) according to item count */
static estimateK(itemCount) {
const k = Math.round(this.BITS_LENGTH / itemCount * Math.LN2);
return Math.max(Math.min(k, this.MAX_K), 1);
}
/**
* new bloom filter instance
* @param k number of hash functions
* @param bits leave it out to construct an empty one
*/
constructor(k, bits) {
if (bits) {
this.bits = bits;
}
else {
this.bits = Buffer.alloc(Bloom.BITS_LENGTH / 8);
}
this.k = k;
}
/**
* add item
* @param item
*/
add(item) {
this.distribute(item, (index, bit) => {
// tslint:disable-next-line:no-bitwise
this.bits[index] |= bit;
return true;
});
}
/**
* test if an item contained. (false positive)
* @param item
*/
test(item) {
return this.distribute(item, (index, bit) => {
// tslint:disable-next-line:no-bitwise
return (this.bits[index] & bit) === bit;
});
}
distribute(item, cb) {
const hash = blake2b256(item);
for (let i = 0; i < this.k; i++) {
// tslint:disable-next-line:no-bitwise
const d = (hash[i * 2 + 1] + (hash[i * 2] << 8)) % Bloom.BITS_LENGTH;
// tslint:disable-next-line:no-bitwise
const bit = 1 << (d % 8);
if (!cb(Math.floor(d / 8), bit)) {
return false;
}
}
return true;
}
}
/** number of hash functions */
Bloom.MAX_K = 16;
/** bit length */
Bloom.BITS_LENGTH = 2048;
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