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https://github.com/codedread/bitjs
synced 2025-10-05 02:19:24 +02:00
Make bitstreams pushable
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codedread
parent
26d06e8d3b
commit
5b10c1a986
3 changed files with 132 additions and 32 deletions
113
io/bitstream.js
113
io/bitstream.js
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@ -34,11 +34,41 @@ bitjs.io.BitStream = class {
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const offset = opt_offset || 0;
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const length = opt_length || ab.byteLength;
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this.bytes = new Uint8Array(ab, offset, length);
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this.pages_ = [];
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this.bytePtr = 0; // tracks which byte we are on
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this.bitPtr = 0; // tracks which bit we are on (can have values 0 through 7)
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this.peekBits = rtl ? this.peekBits_rtl : this.peekBits_ltr;
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}
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/**
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* Returns how many bytes are currently in the stream left to be read.
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* @private
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*/
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getNumBitsLeft_() {
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const bitsLeftInByte = 8 - this.bitPtr;
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const bitsLeftInCurrentPage = (this.bytes.byteLength - this.bytePtr - 1) * 8 + bitsLeftInByte;
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return this.pages_.reduce((acc, arr) => acc + arr.length * 8, bitsLeftInCurrentPage);
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}
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/**
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* Move the pointer ahead n bits. The bytePtr and current page are updated as needed.
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* This is a private method, no validation is done.
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* @param {number} n Number of bits to increment.
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* @private
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*/
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movePointer_(n) {
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this.bitPtr += n;
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while (this.bitPtr >= 8) {
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this.bitPtr -= 8;
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this.bytePtr++;
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while (this.bytePtr >= this.bytes.length && this.pages_.length > 0) {
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this.bytePtr -= this.bytes.length;
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this.bytes = this.pages_.shift();
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}
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}
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}
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/**
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* byte0 byte1 byte2 byte3
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* 7......0 | 7......0 | 7......0 | 7......0
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@ -50,15 +80,22 @@ bitjs.io.BitStream = class {
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* @return {number} The peeked bits, as an unsigned number.
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*/
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peekBits_ltr(n, opt_movePointers) {
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let num = parseInt(n, 10);
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const NUM = parseInt(n, 10);
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let num = NUM;
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if (n !== num || num < 0) {
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throw 'Error! Called peekBits_ltr() with a non-positive integer';
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} else if (num === 0) {
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return 0;
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}
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if (num > this.getNumBitsLeft_()) {
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throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr +
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', bytes.length=' + bytes.length + ', bitPtr=' + bitPtr;
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}
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const movePointers = opt_movePointers || false;
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const bytes = this.bytes;
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let curPage = this.bytes;
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let pageIndex = 0;
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let bytePtr = this.bytePtr;
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let bitPtr = this.bitPtr;
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let result = 0;
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@ -69,24 +106,23 @@ bitjs.io.BitStream = class {
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// shifting/masking it to just extract the bits we want.
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// This could be considerably faster when reading more than 3 or 4 bits at a time.
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while (num > 0) {
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if (bytePtr >= bytes.length) {
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throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr + ', bytes.length=' +
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bytes.length + ', bitPtr=' + bitPtr;
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if (bytePtr >= curPage.length && this.pages_.length > 0) {
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curPage = this.pages_[pageIndex++];
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bytePtr = 0;
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}
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const numBitsLeftInThisByte = (8 - bitPtr);
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if (num >= numBitsLeftInThisByte) {
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const mask = (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] << bitPtr);
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result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
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result |= (((curPage[bytePtr] & mask) >> bitPtr) << bitsIn);
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bytePtr++;
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bitPtr = 0;
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bitsIn += numBitsLeftInThisByte;
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num -= numBitsLeftInThisByte;
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}
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else {
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} else {
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const mask = (bitjs.io.BitStream.BITMASK[num] << bitPtr);
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result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
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result |= (((curPage[bytePtr] & mask) >> bitPtr) << bitsIn);
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bitPtr += num;
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bitsIn += num;
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@ -95,8 +131,7 @@ bitjs.io.BitStream = class {
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}
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if (movePointers) {
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this.bitPtr = bitPtr;
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this.bytePtr = bytePtr;
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this.movePointer_(NUM);
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}
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return result;
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@ -113,15 +148,22 @@ bitjs.io.BitStream = class {
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* @return {number} The peeked bits, as an unsigned number.
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*/
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peekBits_rtl(n, opt_movePointers) {
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let num = parseInt(n, 10);
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const NUM = parseInt(n, 10);
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let num = NUM;
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if (n !== num || num < 0) {
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throw 'Error! Called peekBits_rtl() with a non-positive integer';
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} else if (num === 0) {
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return 0;
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}
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if (num > this.getNumBitsLeft_()) {
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throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr +
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', bytes.length=' + bytes.length + ', bitPtr=' + bitPtr;
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}
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const movePointers = opt_movePointers || false;
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const bytes = this.bytes;
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let curPage = this.bytes;
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let pageIndex = 0;
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let bytePtr = this.bytePtr;
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let bitPtr = this.bitPtr;
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let result = 0;
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@ -131,23 +173,22 @@ bitjs.io.BitStream = class {
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// shifting/masking it to just extract the bits we want.
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// This could be considerably faster when reading more than 3 or 4 bits at a time.
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while (num > 0) {
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if (bytePtr >= bytes.length) {
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throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr + ', bytes.length=' +
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bytes.length + ', bitPtr=' + bitPtr;
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if (bytePtr >= curPage.length && this.pages_.length > 0) {
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curPage = this.pages_[pageIndex++];
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bytePtr = 0;
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}
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const numBitsLeftInThisByte = (8 - bitPtr);
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if (num >= numBitsLeftInThisByte) {
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result <<= numBitsLeftInThisByte;
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result |= (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] & bytes[bytePtr]);
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result |= (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] & curPage[bytePtr]);
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bytePtr++;
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bitPtr = 0;
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num -= numBitsLeftInThisByte;
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}
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else {
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} else {
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result <<= num;
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const numBits = 8 - num - bitPtr;
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result |= ((bytes[bytePtr] & (bitjs.io.BitStream.BITMASK[num] << numBits)) >> numBits);
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result |= ((curPage[bytePtr] & (bitjs.io.BitStream.BITMASK[num] << numBits)) >> numBits);
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bitPtr += num;
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num = 0;
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@ -155,8 +196,7 @@ bitjs.io.BitStream = class {
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}
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if (movePointers) {
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this.bitPtr = bitPtr;
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this.bytePtr = bytePtr;
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this.movePointer_(NUM);
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}
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return result;
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@ -206,14 +246,25 @@ bitjs.io.BitStream = class {
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this.readBits(1);
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}
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if (this.bytePtr + num > this.bytes.byteLength) {
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const numBytesLeft = this.getNumBitsLeft_() / 8;
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if (num > numBytesLeft) {
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throw 'Error! Overflowed the bit stream! n=' + num + ', bytePtr=' + this.bytePtr +
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', bytes.length=' + this.bytes.length + ', bitPtr=' + this.bitPtr;
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}
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const result = this.bytes.subarray(this.bytePtr, this.bytePtr + num);
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const movePointers = opt_movePointers || false;
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const result = new Uint8Array(num);
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let curPage = this.bytes;
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let pageIndex = 0;
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let bytePtr = this.bytePtr;
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for (let i = 0; i < num; ++i) {
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result[i] = curPage[bytePtr++];
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if (bytePtr >= curPage.length) {
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curPage = this.pages_[pageIndex++];
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bytePtr = 0;
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}
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}
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if (movePointers) {
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this.bytePtr += num;
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}
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@ -228,6 +279,18 @@ bitjs.io.BitStream = class {
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readBytes(n) {
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return this.peekBytes(n, true);
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}
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/**
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* Feeds more bytes into the back of the stream.
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* @param {ArrayBuffer} ab
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*/
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push(ab) {
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if (!(ab instanceof ArrayBuffer)) {
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throw 'Error! BitStream.push() called with an invalid ArrayBuffer object';
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}
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this.pages_.push(new Uint8Array(ab));
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}
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}
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// mask for getting N number of bits (0-8)
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@ -13,7 +13,6 @@ var bitjs = bitjs || {};
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bitjs.io = bitjs.io || {};
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// TODO: Add method for pushing bits (multiple arrays) and have tests.
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// TODO: Add method for tee-ing off the stream with tests.
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/**
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* This object allows you to peek and consume bytes as numbers and strings
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@ -41,7 +40,7 @@ bitjs.io.ByteStream = class {
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* Returns how many bytes are currently in the stream left to be read.
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* @private
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*/
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getBytesLeft_() {
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getNumBytesLeft_() {
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const bytesInCurrentPage = (this.bytes.byteLength - this.ptr);
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return this.pages_.reduce((acc, arr) => acc + arr.length, bytesInCurrentPage);
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}
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@ -78,7 +77,7 @@ bitjs.io.ByteStream = class {
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// TODO: Throw an error if n > 4.
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if (this.getBytesLeft_() < num) {
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if (this.getNumBytesLeft_() < num) {
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throw 'Error! Overflowed the byte stream while peekNumber()! n=' + num +
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', ptr=' + this.ptr + ', bytes.length=' + this.bytes.length;
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}
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@ -157,7 +156,7 @@ bitjs.io.ByteStream = class {
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return new Uint8Array();
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}
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const totalBytesLeft = this.getBytesLeft_();
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const totalBytesLeft = this.getNumBytesLeft_();
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if (num > totalBytesLeft) {
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throw 'Error! Overflowed the byte stream! n=' + num + ', ptr=' + this.ptr +
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', bytes.length=' + this.bytes.length;
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@ -204,7 +203,7 @@ bitjs.io.ByteStream = class {
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return '';
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}
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const totalBytesLeft = this.getBytesLeft_();
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const totalBytesLeft = this.getNumBytesLeft_();
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if (num > totalBytesLeft) {
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throw 'Error! Overflowed the byte stream while peekString()! n=' + num +
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', ptr=' + this.ptr + ', bytes.length=' + this.bytes.length;
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@ -243,7 +242,7 @@ bitjs.io.ByteStream = class {
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*/
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push(ab) {
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if (!(ab instanceof ArrayBuffer)) {
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throw 'Error! push() called with an invalid ArrayBuffer object';
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throw 'Error! ByteStream.push() called with an invalid ArrayBuffer object';
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}
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this.pages_.push(new Uint8Array(ab));
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@ -73,7 +73,45 @@
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assertThrows(() => stream.readBytes(3),
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'Did not throw when trying to read bytes past the end of the stream');
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}
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},
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testBitStreamReadAfterPush_RTL() {
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array = new Uint8Array(1);
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array[0] = Number('0b01010110');
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const stream = new bitjs.io.BitStream(array.buffer, true /* rtl */);
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const readBits = stream.readBits(8);
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assertEquals(0x56, readBits, 'Could not read 8 bits: ' + readBits);
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assertThrows(() => stream.readBits(4),
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'Did not throw when trying to read a bit past the end of the stream');
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const anotherArray = new Uint8Array(1);
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anotherArray[0] = Number('0b01010110');
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stream.push(anotherArray.buffer);
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assertEquals(0x5, stream.readBits(4),
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'Could not read in next 4 bits after pushing in RTL');
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assertEquals(0x6, stream.readBits(4),
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'Could not read in next 4 bits after pushing in RTL');
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},
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testBitStreamReadAfterPush_LTR() {
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array = new Uint8Array(1);
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array[0] = Number('0b01010110');
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const stream = new bitjs.io.BitStream(array.buffer, false /* rtl */);
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const readBits = stream.readBits(8);
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assertEquals(0x56, readBits, 'Could not read 8 bits: ' + readBits);
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assertThrows(() => stream.readBits(4),
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'Did not throw when trying to read a bit past the end of the stream');
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const anotherArray = new Uint8Array(1);
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anotherArray[0] = Number('0b01010110');
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stream.push(anotherArray.buffer);
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assertEquals(0x6, stream.readBits(4),
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'Could not read in next 4 bits after pushing in LTR');
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assertEquals(0x5, stream.readBits(4),
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'Could not read in next 4 bits after pushing in LTR');
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},
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},
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});
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</script>
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