@msgpack/msgpack/dist.esm/CachedKeyDecoder.mjs

MessagePack for ECMA-262/JavaScript/TypeScript

import { utf8DecodeJs } from "./utils/utf8.mjs";
const DEFAULT_MAX_KEY_LENGTH = 16;
const DEFAULT_MAX_LENGTH_PER_KEY = 16;
export class CachedKeyDecoder {
    hit = 0;
    miss = 0;
    caches;
    maxKeyLength;
    maxLengthPerKey;
    constructor(maxKeyLength = DEFAULT_MAX_KEY_LENGTH, maxLengthPerKey = DEFAULT_MAX_LENGTH_PER_KEY) {
        this.maxKeyLength = maxKeyLength;
        this.maxLengthPerKey = maxLengthPerKey;
        // avoid `new Array(N)`, which makes a sparse array,
        // because a sparse array is typically slower than a non-sparse array.
        this.caches = [];
        for (let i = 0; i < this.maxKeyLength; i++) {
            this.caches.push([]);
        }
    }
    canBeCached(byteLength) {
        return byteLength > 0 && byteLength <= this.maxKeyLength;
    }
    find(bytes, inputOffset, byteLength) {
        const records = this.caches[byteLength - 1];
        FIND_CHUNK: for (const record of records) {
            const recordBytes = record.bytes;
            for (let j = 0; j < byteLength; j++) {
                if (recordBytes[j] !== bytes[inputOffset + j]) {
                    continue FIND_CHUNK;
                }
            }
            return record.str;
        }
        return null;
    }
    store(bytes, value) {
        const records = this.caches[bytes.length - 1];
        const record = { bytes, str: value };
        if (records.length >= this.maxLengthPerKey) {
            // `records` are full!
            // Set `record` to an arbitrary position.
            records[(Math.random() * records.length) | 0] = record;
        }
        else {
            records.push(record);
        }
    }
    decode(bytes, inputOffset, byteLength) {
        const cachedValue = this.find(bytes, inputOffset, byteLength);
        if (cachedValue != null) {
            this.hit++;
            return cachedValue;
        }
        this.miss++;
        const str = utf8DecodeJs(bytes, inputOffset, byteLength);
        // Ensure to copy a slice of bytes because the bytes may be a NodeJS Buffer and Buffer#slice() returns a reference to its internal ArrayBuffer.
        const slicedCopyOfBytes = Uint8Array.prototype.slice.call(bytes, inputOffset, inputOffset + byteLength);
        this.store(slicedCopyOfBytes, str);
        return str;
    }
}
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