1// Copyright (C) 2024 The Android Open Source Project 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15import {assertTrue} from './logging'; 16 17/** 18 * A dynamically resizable array buffer implementation for efficient 19 * storage and manipulation of binary data. It starts with a specified 20 * initial size and grows as needed to accommodate appended data. 21 * Efficiently grows the buffer using an exponential strategy up to 32MB, 22 * and then linearly in 32MB increments to minimize reallocation overhead. 23 * Provides methods to append data, shrink the size, clear the buffer, 24 * and retrieve the stored data as a `Uint8Array`. 25 */ 26export class ResizableArrayBuffer { 27 private buf: Uint8Array; 28 private _size = 0; 29 30 constructor(private readonly initialSize = 128) { 31 this.buf = new Uint8Array(initialSize); 32 } 33 34 append(data: ArrayLike<number>) { 35 const capacityNeeded = this._size + data.length; 36 if (this.capacity < capacityNeeded) { 37 this.grow(capacityNeeded); 38 } 39 this.buf.set(data, this._size); 40 this._size = capacityNeeded; 41 } 42 43 shrink(newSize: number) { 44 assertTrue(newSize <= this._size); 45 this._size = newSize; 46 } 47 48 clear() { 49 this.buf = new Uint8Array(this.initialSize); 50 this._size = 0; 51 } 52 53 get(): Uint8Array { 54 return this.buf.subarray(0, this._size); 55 } 56 57 get size(): number { 58 return this._size; 59 } 60 61 get capacity(): number { 62 return this.buf.length; 63 } 64 65 private grow(capacityNeeded: number) { 66 let newSize = this.buf.length; 67 const MB32 = 32 * 1024 * 1024; 68 do { 69 newSize = newSize < MB32 ? newSize * 2 : newSize + MB32; 70 } while (newSize < capacityNeeded); 71 const newBuf = new Uint8Array(newSize); 72 assertTrue(newBuf.length >= capacityNeeded); 73 newBuf.set(this.buf); 74 this.buf = newBuf; 75 } 76} 77