next/dist/esm/shared/lib/bloom-filter.js

The React Framework

// minimal implementation MurmurHash2 hash function
function murmurhash2(str) {
    let h = 0;
    for(let i = 0; i < str.length; i++){
        const c = str.charCodeAt(i);
        h = Math.imul(h ^ c, 0x5bd1e995);
        h ^= h >>> 13;
        h = Math.imul(h, 0x5bd1e995);
    }
    return h >>> 0;
}
// default to 0.01% error rate as the filter compresses very well
const DEFAULT_ERROR_RATE = 0.0001;
export class BloomFilter {
    static from(items, errorRate) {
        if (errorRate === void 0) errorRate = DEFAULT_ERROR_RATE;
        const filter = new BloomFilter(items.length, errorRate);
        for (const item of items){
            filter.add(item);
        }
        return filter;
    }
    export() {
        const data = {
            numItems: this.numItems,
            errorRate: this.errorRate,
            numBits: this.numBits,
            numHashes: this.numHashes,
            bitArray: this.bitArray
        };
        if (process.env.NEXT_RUNTIME === 'nodejs') {
            if (this.errorRate < DEFAULT_ERROR_RATE) {
                const filterData = JSON.stringify(data);
                const gzipSize = require('next/dist/compiled/gzip-size').sync(filterData);
                if (gzipSize > 1024) {
                    console.warn("Creating filter with error rate less than 0.1% (0.001) can increase the size dramatically proceed with caution. Received error rate " + this.errorRate + " resulted in size " + filterData.length + " bytes, " + gzipSize + " bytes (gzip)");
                }
            }
        }
        return data;
    }
    import(data) {
        this.numItems = data.numItems;
        this.errorRate = data.errorRate;
        this.numBits = data.numBits;
        this.numHashes = data.numHashes;
        this.bitArray = data.bitArray;
    }
    add(item) {
        const hashValues = this.getHashValues(item);
        hashValues.forEach((hash)=>{
            this.bitArray[hash] = 1;
        });
    }
    contains(item) {
        const hashValues = this.getHashValues(item);
        return hashValues.every((hash)=>this.bitArray[hash]);
    }
    getHashValues(item) {
        const hashValues = [];
        for(let i = 1; i <= this.numHashes; i++){
            const hash = murmurhash2("" + item + i) % this.numBits;
            hashValues.push(hash);
        }
        return hashValues;
    }
    constructor(numItems, errorRate = DEFAULT_ERROR_RATE){
        this.numItems = numItems;
        this.errorRate = errorRate;
        this.numBits = Math.ceil(-(numItems * Math.log(errorRate)) / (Math.log(2) * Math.log(2)));
        this.numHashes = Math.ceil(this.numBits / numItems * Math.log(2));
        this.bitArray = new Array(this.numBits).fill(0);
    }
}

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