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Make bitstreams pushable

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codedread 2018-01-21 01:49:17 -08:00
parent 26d06e8d3b
commit 5b10c1a986
3 changed files with 132 additions and 32 deletions
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113
io/bitstream.js
View file

@ -34,11 +34,41 @@ bitjs.io.BitStream = class {
const offset = opt_offset || 0;
const length = opt_length || ab.byteLength;
this.bytes = new Uint8Array(ab, offset, length);
this.pages_ = [];
this.bytePtr = 0; // tracks which byte we are on
this.bitPtr = 0; // tracks which bit we are on (can have values 0 through 7)
this.peekBits = rtl ? this.peekBits_rtl : this.peekBits_ltr;
}
/**
* Returns how many bytes are currently in the stream left to be read.
* @private
*/
getNumBitsLeft_() {
const bitsLeftInByte = 8 - this.bitPtr;
const bitsLeftInCurrentPage = (this.bytes.byteLength - this.bytePtr - 1) * 8 + bitsLeftInByte;
return this.pages_.reduce((acc, arr) => acc + arr.length * 8, bitsLeftInCurrentPage);
}
/**
* Move the pointer ahead n bits. The bytePtr and current page are updated as needed.
* This is a private method, no validation is done.
* @param {number} n Number of bits to increment.
* @private
*/
movePointer_(n) {
this.bitPtr += n;
while (this.bitPtr >= 8) {
this.bitPtr -= 8;
this.bytePtr++;
while (this.bytePtr >= this.bytes.length && this.pages_.length > 0) {
this.bytePtr -= this.bytes.length;
this.bytes = this.pages_.shift();
}
}
}
/**
* byte0 byte1 byte2 byte3
* 7......0 | 7......0 | 7......0 | 7......0
@ -50,15 +80,22 @@ bitjs.io.BitStream = class {
* @return {number} The peeked bits, as an unsigned number.
*/
peekBits_ltr(n, opt_movePointers) {
let num = parseInt(n, 10);
const NUM = parseInt(n, 10);
let num = NUM;
if (n !== num || num < 0) {
throw 'Error! Called peekBits_ltr() with a non-positive integer';
} else if (num === 0) {
return 0;
}
if (num > this.getNumBitsLeft_()) {
throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr +
', bytes.length=' + bytes.length + ', bitPtr=' + bitPtr;
}
const movePointers = opt_movePointers || false;
const bytes = this.bytes;
let curPage = this.bytes;
let pageIndex = 0;
let bytePtr = this.bytePtr;
let bitPtr = this.bitPtr;
let result = 0;
@ -69,24 +106,23 @@ bitjs.io.BitStream = class {
// shifting/masking it to just extract the bits we want.
// This could be considerably faster when reading more than 3 or 4 bits at a time.
while (num > 0) {
if (bytePtr >= bytes.length) {
throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr + ', bytes.length=' +
bytes.length + ', bitPtr=' + bitPtr;
if (bytePtr >= curPage.length && this.pages_.length > 0) {
curPage = this.pages_[pageIndex++];
bytePtr = 0;
}
const numBitsLeftInThisByte = (8 - bitPtr);
if (num >= numBitsLeftInThisByte) {
const mask = (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
result |= (((curPage[bytePtr] & mask) >> bitPtr) << bitsIn);
bytePtr++;
bitPtr = 0;
bitsIn += numBitsLeftInThisByte;
num -= numBitsLeftInThisByte;
}
else {
} else {
const mask = (bitjs.io.BitStream.BITMASK[num] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
result |= (((curPage[bytePtr] & mask) >> bitPtr) << bitsIn);
bitPtr += num;
bitsIn += num;
@ -95,8 +131,7 @@ bitjs.io.BitStream = class {
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
this.movePointer_(NUM);
}
return result;
@ -113,15 +148,22 @@ bitjs.io.BitStream = class {
* @return {number} The peeked bits, as an unsigned number.
*/
peekBits_rtl(n, opt_movePointers) {
let num = parseInt(n, 10);
const NUM = parseInt(n, 10);
let num = NUM;
if (n !== num || num < 0) {
throw 'Error! Called peekBits_rtl() with a non-positive integer';
} else if (num === 0) {
return 0;
}
if (num > this.getNumBitsLeft_()) {
throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr +
', bytes.length=' + bytes.length + ', bitPtr=' + bitPtr;
}
const movePointers = opt_movePointers || false;
const bytes = this.bytes;
let curPage = this.bytes;
let pageIndex = 0;
let bytePtr = this.bytePtr;
let bitPtr = this.bitPtr;
let result = 0;
@ -131,23 +173,22 @@ bitjs.io.BitStream = class {
// shifting/masking it to just extract the bits we want.
// This could be considerably faster when reading more than 3 or 4 bits at a time.
while (num > 0) {
if (bytePtr >= bytes.length) {
throw 'Error! Overflowed the bit stream! n=' + n + ', bytePtr=' + bytePtr + ', bytes.length=' +
bytes.length + ', bitPtr=' + bitPtr;
if (bytePtr >= curPage.length && this.pages_.length > 0) {
curPage = this.pages_[pageIndex++];
bytePtr = 0;
}
const numBitsLeftInThisByte = (8 - bitPtr);
if (num >= numBitsLeftInThisByte) {
result <<= numBitsLeftInThisByte;
result |= (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] & bytes[bytePtr]);
result |= (bitjs.io.BitStream.BITMASK[numBitsLeftInThisByte] & curPage[bytePtr]);
bytePtr++;
bitPtr = 0;
num -= numBitsLeftInThisByte;
}
else {
} else {
result <<= num;
const numBits = 8 - num - bitPtr;
result |= ((bytes[bytePtr] & (bitjs.io.BitStream.BITMASK[num] << numBits)) >> numBits);
result |= ((curPage[bytePtr] & (bitjs.io.BitStream.BITMASK[num] << numBits)) >> numBits);
bitPtr += num;
num = 0;
@ -155,8 +196,7 @@ bitjs.io.BitStream = class {
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
this.movePointer_(NUM);
}
return result;
@ -206,14 +246,25 @@ bitjs.io.BitStream = class {
this.readBits(1);
}
if (this.bytePtr + num > this.bytes.byteLength) {
const numBytesLeft = this.getNumBitsLeft_() / 8;
if (num > numBytesLeft) {
throw 'Error! Overflowed the bit stream! n=' + num + ', bytePtr=' + this.bytePtr +
', bytes.length=' + this.bytes.length + ', bitPtr=' + this.bitPtr;
}
const result = this.bytes.subarray(this.bytePtr, this.bytePtr + num);
const movePointers = opt_movePointers || false;
const result = new Uint8Array(num);
let curPage = this.bytes;
let pageIndex = 0;
let bytePtr = this.bytePtr;
for (let i = 0; i < num; ++i) {
result[i] = curPage[bytePtr++];
if (bytePtr >= curPage.length) {
curPage = this.pages_[pageIndex++];
bytePtr = 0;
}
}
if (movePointers) {
this.bytePtr += num;
}
@ -228,6 +279,18 @@ bitjs.io.BitStream = class {
readBytes(n) {
return this.peekBytes(n, true);
}
/**
* Feeds more bytes into the back of the stream.
* @param {ArrayBuffer} ab
*/
push(ab) {
if (!(ab instanceof ArrayBuffer)) {
throw 'Error! BitStream.push() called with an invalid ArrayBuffer object';
}
this.pages_.push(new Uint8Array(ab));
}
}
// mask for getting N number of bits (0-8)

11
io/bytestream.js
View file

@ -13,7 +13,6 @@ var bitjs = bitjs || {};
bitjs.io = bitjs.io || {};
// TODO: Add method for pushing bits (multiple arrays) and have tests.
// TODO: Add method for tee-ing off the stream with tests.
/**
* This object allows you to peek and consume bytes as numbers and strings
@ -41,7 +40,7 @@ bitjs.io.ByteStream = class {
* Returns how many bytes are currently in the stream left to be read.
* @private
*/
getBytesLeft_() {
getNumBytesLeft_() {
const bytesInCurrentPage = (this.bytes.byteLength - this.ptr);
return this.pages_.reduce((acc, arr) => acc + arr.length, bytesInCurrentPage);
}
@ -78,7 +77,7 @@ bitjs.io.ByteStream = class {
// TODO: Throw an error if n > 4.
if (this.getBytesLeft_() < num) {
if (this.getNumBytesLeft_() < num) {
throw 'Error! Overflowed the byte stream while peekNumber()! n=' + num +
', ptr=' + this.ptr + ', bytes.length=' + this.bytes.length;
}
@ -157,7 +156,7 @@ bitjs.io.ByteStream = class {
return new Uint8Array();
}
const totalBytesLeft = this.getBytesLeft_();
const totalBytesLeft = this.getNumBytesLeft_();
if (num > totalBytesLeft) {
throw 'Error! Overflowed the byte stream! n=' + num + ', ptr=' + this.ptr +
', bytes.length=' + this.bytes.length;
@ -204,7 +203,7 @@ bitjs.io.ByteStream = class {
return '';
}
const totalBytesLeft = this.getBytesLeft_();
const totalBytesLeft = this.getNumBytesLeft_();
if (num > totalBytesLeft) {
throw 'Error! Overflowed the byte stream while peekString()! n=' + num +
', ptr=' + this.ptr + ', bytes.length=' + this.bytes.length;
@ -243,7 +242,7 @@ bitjs.io.ByteStream = class {
*/
push(ab) {
if (!(ab instanceof ArrayBuffer)) {
throw 'Error! push() called with an invalid ArrayBuffer object';
throw 'Error! ByteStream.push() called with an invalid ArrayBuffer object';
}
this.pages_.push(new Uint8Array(ab));

40
tests/io-bitstream-test.html
View file

@ -73,7 +73,45 @@
assertThrows(() => stream.readBytes(3),
'Did not throw when trying to read bytes past the end of the stream');
}
},
testBitStreamReadAfterPush_RTL() {
array = new Uint8Array(1);
array[0] = Number('0b01010110');
const stream = new bitjs.io.BitStream(array.buffer, true /* rtl */);
const readBits = stream.readBits(8);
assertEquals(0x56, readBits, 'Could not read 8 bits: ' + readBits);
assertThrows(() => stream.readBits(4),
'Did not throw when trying to read a bit past the end of the stream');
const anotherArray = new Uint8Array(1);
anotherArray[0] = Number('0b01010110');
stream.push(anotherArray.buffer);
assertEquals(0x5, stream.readBits(4),
'Could not read in next 4 bits after pushing in RTL');
assertEquals(0x6, stream.readBits(4),
'Could not read in next 4 bits after pushing in RTL');
},
testBitStreamReadAfterPush_LTR() {
array = new Uint8Array(1);
array[0] = Number('0b01010110');
const stream = new bitjs.io.BitStream(array.buffer, false /* rtl */);
const readBits = stream.readBits(8);
assertEquals(0x56, readBits, 'Could not read 8 bits: ' + readBits);
assertThrows(() => stream.readBits(4),
'Did not throw when trying to read a bit past the end of the stream');
const anotherArray = new Uint8Array(1);
anotherArray[0] = Number('0b01010110');
stream.push(anotherArray.buffer);
assertEquals(0x6, stream.readBits(4),
'Could not read in next 4 bits after pushing in LTR');
assertEquals(0x5, stream.readBits(4),
'Could not read in next 4 bits after pushing in LTR');
},
},
});
</script>