TypeScript power-of-two ring buffer (circular buffer)

ring-buffer.ts

// Copyright 2020 Dusk <[email protected]>
// SPDX-License-Identifier: 0BSD

class RingBuffer<T> {
  buffer: T[];
  readIx: number;
  writeIx: number;
  ixMask: number;
  canGrow: boolean;
  canDrop: boolean;

  constructor(capacity: number, canGrow: boolean, canDrop: boolean) {
    capacity = capacity + 1;
    if (!Number.isInteger(capacity) || capacity > 0x8000_0000) {
      throw "ring buffer capacity must be a non-negative integer <= (2**31 - 1)";
    } else if (capacity !== 0 && (capacity & (capacity - 1)) !== 0) {
      throw "ring buffer capacity must be a (power of 2) - 1";
    }
    this.buffer = new Array(capacity);
    this.readIx = 0, this.writeIx = 0;
    this.ixMask = (capacity - 1) | 0;
    this.canGrow = canGrow, this.canDrop = canDrop;
  }

  get capacity(): number { return this.buffer.length - 1; }
  isEmpty() { return this.writeIx === this.readIx; }
  isFull() { return ((this.writeIx + 1) & this.ixMask) === this.readIx; }
  get length(): number { return (this.writeIx - this.readIx) & this.ixMask; }

  grow(): number | undefined {
    const buffer = this.buffer;
    if (!this.canGrow || buffer.length === 0x8000_0000) { return undefined; }
    let oldCapacity = buffer.length;
    let capacity = oldCapacity << 1;
    buffer.length = capacity;
    this.ixMask = this.ixMask = (capacity - 1) | 0;
    const writeIx = this.writeIx;
    if (writeIx < this.readIx) {
      // capacity has been doubled, so tmpWriteIx can't wrap around to 0 while copying old elements
      for (let tmpReadIx = 0, tmpWriteIx = oldCapacity; tmpReadIx !== writeIx; ++tmpReadIx, ++tmpWriteIx) {
        buffer[tmpWriteIx] = buffer[tmpReadIx];
        delete buffer[tmpReadIx];
      }
      this.writeIx = writeIx + oldCapacity;
    }
    return capacity;
  }
  
  replace(element: T): T | undefined {
    let writeIx = this.writeIx;
    if (writeIx === this.readIx) { return undefined; }
    return this.buffer[writeIx] = element;
  }
  push(element: T): T | undefined {
    let buffer = this.buffer, readIx = this.readIx, writeIx = this.writeIx, ixMask = this.ixMask;
    if (((writeIx + 1) & ixMask) === readIx) {
      if (this.grow() !== undefined) {
        writeIx = this.writeIx, ixMask = this.ixMask;
      } else if (this.canDrop) {
        delete buffer[readIx];
        this.readIx = (readIx + 1) & ixMask;
      } else { return undefined; }
    }
    buffer[writeIx] = element;
    this.writeIx = (writeIx + 1) & ixMask;
    return element;
  }
  peek(): T | undefined { return this.buffer[this.readIx]; }
  pop(): T | undefined { let element = this.peek(); this.drop(); return element; }
  drop(): boolean {
    let readIx = this.readIx;
    if (this.writeIx === readIx) { return false; }
    delete this.buffer[readIx];
    this.readIx = (readIx + 1) & this.ixMask;
    return true;
  }
}

(function () {
  let buf = new RingBuffer(3, false, true);
  let log = function (...args: any[]): void {
    return console.log(...args, buf.buffer, buf.readIx, buf.writeIx);
  }
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('push', buf.push(0));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('push', buf.push(1));
  log('push', buf.push(2));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('push', buf.push(3));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  log('pop', buf.pop());
  log('pop', buf.pop());
  log('push', buf.push('a'));
  log('push', buf.push('b'));
  log('pop', buf.pop());
  log('push', buf.push('c'));
  log('length', buf.length);
  log('pop', buf.pop());
  log('push', buf.push('d'));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('push', buf.push('e'));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  log('pop', buf.pop());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('push', buf.push('f'));
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
  log('pop', buf.pop());
  console.log('isEmpty', buf.isEmpty(), 'isFull', buf.isFull());
})()