@syncfusion/ej2-pdf
Version:
Feature-rich JavaScript PDF library with built-in support for loading and manipulating PDF document.
151 lines (150 loc) • 6.25 kB
JavaScript
var __extends = (this && this.__extends) || (function () {
var extendStatics = function (d, b) {
extendStatics = Object.setPrototypeOf ||
({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
return extendStatics(d, b);
};
return function (d, b) {
extendStatics(d, b);
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
})();
import { _PdfDecodeStream } from '../decode-stream';
/**
* Provides an LZW decoding stream that expands LZW compressed data from the underlying stream.
*
* @private
*/
var _PdfLempelZivWelchStream = /** @class */ (function (_super) {
__extends(_PdfLempelZivWelchStream, _super);
function _PdfLempelZivWelchStream(str, maybeLength, earlyChange) {
var _this = _super.call(this, maybeLength) || this;
_this.stream = str;
_this.cachedData = 0;
_this.bitsCached = 0;
var maxLzwDictionarySize = 4096;
var lzwState = {
earlyChange: earlyChange || 0,
codeLength: 9,
nextCode: 258,
dictionaryValues: new Uint8Array(maxLzwDictionarySize),
dictionaryLengths: new Uint16Array(maxLzwDictionarySize),
dictionaryPrevCodes: new Uint16Array(maxLzwDictionarySize),
currentSequence: new Uint8Array(maxLzwDictionarySize),
currentSequenceLength: 0
};
for (var i = 0; i < 256; ++i) {
lzwState.dictionaryValues[i] = i;
lzwState.dictionaryLengths[i] = 1;
}
_this.lzwState = lzwState;
_this.lastCode = null;
return _this;
}
_PdfLempelZivWelchStream.prototype.readBits = function (n) {
var bitsCached = this.bitsCached;
var cachedData = this.cachedData;
while (bitsCached < n) {
var c = this.stream.getByte(); // eslint-disable-line
if (c === -1) {
this.eof = true;
return null;
}
cachedData = (cachedData << 8) | c;
bitsCached += 8;
}
this.bitsCached = bitsCached -= n;
this.cachedData = cachedData;
this.lastCode = null;
return (cachedData >>> bitsCached) & ((1 << n) - 1);
};
_PdfLempelZivWelchStream.prototype.readBlock = function () {
var blockSize = 512;
var decodedSizeDelta = blockSize;
var estimatedDecodedSize = blockSize * 2;
var i;
var j;
var q;
var lzwState = this.lzwState; // eslint-disable-line
if (!lzwState) {
return;
}
var earlyChange = lzwState.earlyChange; // eslint-disable-line
var nextCode = lzwState.nextCode; // eslint-disable-line
var dictionaryValues = lzwState.dictionaryValues; // eslint-disable-line
var dictionaryLengths = lzwState.dictionaryLengths; // eslint-disable-line
var dictionaryPrevCodes = lzwState.dictionaryPrevCodes; // eslint-disable-line
var codeLength = lzwState.codeLength; // eslint-disable-line
var prevCode = lzwState.prevCode; // eslint-disable-line
var currentSequence = lzwState.currentSequence; // eslint-disable-line
var currentSequenceLength = lzwState.currentSequenceLength;
var decodedLength = 0;
var currentBufferLength = this.bufferLength;
var buffer = this.ensureBuffer(this.bufferLength + estimatedDecodedSize); // eslint-disable-line
for (i = 0; i < blockSize; i++) {
var code = this.readBits(codeLength);
var hasPrev = currentSequenceLength > 0;
if (code === null) {
break;
}
if (code < 256) {
currentSequence[0] = code;
currentSequenceLength = 1;
}
else if (code >= 258) {
if (code < nextCode) {
currentSequenceLength = dictionaryLengths[code];
for (j = currentSequenceLength - 1, q = code; j >= 0; j--) {
currentSequence[j] = dictionaryValues[q];
q = dictionaryPrevCodes[q];
}
}
else {
currentSequence[currentSequenceLength++] = currentSequence[0];
}
}
else if (code === 256) {
codeLength = 9;
nextCode = 258;
currentSequenceLength = 0;
continue;
}
else {
this.eof = true;
this.lzwState = null;
break;
}
if (hasPrev) {
dictionaryPrevCodes[nextCode] = prevCode;
dictionaryLengths[nextCode] = dictionaryLengths[prevCode] + 1;
dictionaryValues[nextCode] = currentSequence[0];
nextCode++;
codeLength =
((nextCode + earlyChange) & (nextCode + earlyChange - 1))
? codeLength
: Math.min(((Math.log(nextCode + earlyChange) / 0.6931471805599453) + 1) | 0, 12);
}
prevCode = code;
decodedLength += currentSequenceLength;
if (estimatedDecodedSize < decodedLength) {
do {
estimatedDecodedSize += decodedSizeDelta;
} while (estimatedDecodedSize < decodedLength);
buffer = this.ensureBuffer(this.bufferLength + estimatedDecodedSize);
}
for (j = 0; j < currentSequenceLength; j++) {
buffer[currentBufferLength] = currentSequence[j];
currentBufferLength++;
}
}
lzwState.nextCode = nextCode;
lzwState.codeLength = codeLength;
lzwState.prevCode = prevCode;
lzwState.currentSequenceLength = currentSequenceLength;
this.bufferLength = currentBufferLength;
};
return _PdfLempelZivWelchStream;
}(_PdfDecodeStream));
export { _PdfLempelZivWelchStream };