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Added the ability to specify leftMostBitFirst

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h345983745 2019-08-24 19:07:44 +01:00
parent 54286784a7
commit 3ebec7117b
1 changed files with 42 additions and 19 deletions
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31
src/core/lib/Stream.mjs
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@ -93,17 +93,40 @@ export default class Stream {
/**
* Reads a number of bits from the buffer.
*
* @TODO Add endianness
*
* @param {number} numBits
* @param {bool} [leftMostBitFirst=false]
* @returns {number}
*/
readBits(numBits) {
readBits(numBits, leftMostBitFirst=false) {
if (this.position > this.length) return undefined;
let bitBuf = 0,
bitBufLen = 0;
if (leftMostBitFirst) {
// Add remaining bits from current byte
const mask = ((1 << (8 - this.bitPos)) -1);
bitBuf = this.bytes[this.position++] & mask;
bitBufLen = 8 - this.bitPos;
this.bitPos = 0;
// Not enough bits yet
while (bitBufLen < numBits) {
bitBuf = (bitBuf << 8) | this.bytes[this.position++];
bitBufLen += 8;
}
// Reverse back to numBits
const excess = bitBufLen - numBits;
bitBuf = bitBuf >> excess;
bitBufLen -= excess;
this.position--;
this.bitPos = 8 - excess;
return bitBuf;
} else {
// Add remaining bits from current byte
bitBuf = (this.bytes[this.position++] & bitMask(this.bitPos)) >>> this.bitPos;
bitBufLen = 8 - this.bitPos;
@ -125,7 +148,7 @@ export default class Stream {
}
return bitBuf;
}
/**
* Calculates the bit mask based on the current bit position.
*