image-in-browser/lib/formats/tiff/tiff-lzw-decoder.js

Package for encoding / decoding images, transforming images, applying filters, drawing primitives on images on the client side (no need for server Node.js)

import { LibError } from '../../error/lib-error.js';
export class LzwDecoder {
    constructor() {
        this._buffer = new Uint8Array(4096);
        this._bitsToGet = 9;
        this._bytePointer = 0;
        this._nextData = 0;
        this._nextBits = 0;
    }
    addString(string, newString) {
        this._table[this._tableIndex] = newString;
        this._prefix[this._tableIndex] = string;
        this._tableIndex = this._tableIndex + 1;
        if (this._tableIndex === 511) {
            this._bitsToGet = 10;
        }
        else if (this._tableIndex === 1023) {
            this._bitsToGet = 11;
        }
        else if (this._tableIndex === 2047) {
            this._bitsToGet = 12;
        }
    }
    getString(code) {
        this._bufferLength = 0;
        let c = code;
        this._buffer[this._bufferLength++] = this._table[c];
        c = this._prefix[c];
        while (c !== LzwDecoder._noSuchCode) {
            this._buffer[this._bufferLength++] = this._table[c];
            c = this._prefix[c];
        }
    }
    getNextCode() {
        if (this._bytePointer >= this._dataLength) {
            return 257;
        }
        while (this._nextBits < this._bitsToGet) {
            if (this._bytePointer >= this._dataLength) {
                return 257;
            }
            this._nextData =
                ((this._nextData << 8) + this._data[this._bytePointer++]) & 0xffffffff;
            this._nextBits += 8;
        }
        this._nextBits -= this._bitsToGet;
        const code = (this._nextData >>> this._nextBits) &
            LzwDecoder._andTable[this._bitsToGet - 9];
        return code;
    }
    initializeStringTable() {
        this._table = new Uint8Array(LzwDecoder._lzMaxCode + 1);
        this._prefix = new Uint32Array(LzwDecoder._lzMaxCode + 1);
        this._prefix.fill(LzwDecoder._noSuchCode, 0, this._prefix.length);
        for (let i = 0; i < 256; i++) {
            this._table[i] = i;
        }
        this._bitsToGet = 9;
        this._tableIndex = 258;
    }
    decode(p, out) {
        this._out = out;
        const outLen = out.length;
        this._outPointer = 0;
        this._data = p.buffer;
        this._dataLength = this._data.length;
        this._bytePointer = p.offset;
        if (this._data[0] === 0x00 && this._data[1] === 0x01) {
            throw new LibError('Invalid LZW Data');
        }
        this.initializeStringTable();
        this._nextData = 0;
        this._nextBits = 0;
        let oldCode = 0;
        let code = this.getNextCode();
        while (code !== 257 && this._outPointer < outLen) {
            if (code === 256) {
                this.initializeStringTable();
                code = this.getNextCode();
                this._bufferLength = 0;
                if (code === 257) {
                    break;
                }
                this._out[this._outPointer++] = code;
                oldCode = code;
            }
            else {
                if (code < this._tableIndex) {
                    this.getString(code);
                    for (let i = this._bufferLength - 1; i >= 0; --i) {
                        this._out[this._outPointer++] = this._buffer[i];
                    }
                    this.addString(oldCode, this._buffer[this._bufferLength - 1]);
                    oldCode = code;
                }
                else {
                    this.getString(oldCode);
                    for (let i = this._bufferLength - 1; i >= 0; --i) {
                        this._out[this._outPointer++] = this._buffer[i];
                    }
                    this._out[this._outPointer++] = this._buffer[this._bufferLength - 1];
                    this.addString(oldCode, this._buffer[this._bufferLength - 1]);
                    oldCode = code;
                }
            }
            code = this.getNextCode();
        }
    }
}
LzwDecoder._lzMaxCode = 4095;
LzwDecoder._noSuchCode = 4098;
LzwDecoder._andTable = [511, 1023, 2047, 4095];
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