functional set bit, clear bit, read bit, slice
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1 changed files with 61 additions and 32 deletions
91
js/utils.js
91
js/utils.js
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@ -184,40 +184,88 @@ Base64 = (function () {
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throw new RangeError("Numerical data has to fit within a 32-bit integer range to instantiate a BitVector.");
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}
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bit_vec.push(data);
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} else if (data instanceof Array) [
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} else if (data instanceof Array) {
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]
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}
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this.length = length;
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this.bits = new Uint32Array(bit_vec);
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}
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readBitsSigned() {
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/** Return value of bit at index idx.
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*
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* @param {Number} idx - the index to read
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*/
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read_bit(idx) {
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if (idx < 0 || idx > this.length) {
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throw new RangeError("Cannot read bit outside the range of the BitVector.");
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}
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return ((this.bits[Math.floor(idx / 32)] & (1 << (idx % 32))) == 0 ? 0 : 1);
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}
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readBitsUnsigned() {
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/** Returns an integer value (if possible) made from the range of bits [start, end). Undefined behavior if the range to read is too big.
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*
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* @param {Number} start - the index to start slicing from. Inclusive
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* @param {Number} end - the index to end slicing at. Exclusive
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*/
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slice(start, end) {
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if (end < start) {
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throw new RangeError("Cannot slice a range where the end is before the start.");
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} else if (end == start) {
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return 0;
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}
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setBits() {
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let res = 0;
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if (Math.floor((end - 1) / 32) == Math.floor(start / 32)) {
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//the range is within 1 uint32 section - do some relatively fast bit twiddling
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res = (this.bits[Math.floor(start / 32)] & ~((((~0) << ((end - 1) % 32)) << 1) | ~((~0) << (start % 32)))) >>> (start % 32);
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} else {
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//range is not within 1 section of the array - do ugly
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for (let i = start; i < end; i++) {
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res |= (get_bit(i) << (i - start));
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}
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}
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clearBits() {
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return res;
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}
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/** Assign bit at index idx to 1.
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*
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* @param {Number} idx - the index to set
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*/
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set_bit(idx) {
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if (idx < 0 || idx > this.length) {
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throw new RangeError("Cannot set bit outside the range of the BitVector.");
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}
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this.bits[Math.floor(idx / 32)] |= (1 << idx % 32);
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}
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/** Assign bit at index idx to 0.
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*
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* @param {Number} idx - the index to clear
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*/
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clear_bit(idx) {
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if (idx < 0 || idx > this.length) {
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throw new RangeError("Cannot clear bit outside the range of the BitVector.");
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}
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this.bits[Math.floor(idx / 32)] &= ~(1 << idx % 32);
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}
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/** Appends data to the BitVector.
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*
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* @param {Number | String | Array} data
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* @param {Number} length - the length, in bits, of the new data
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*/
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append(data, length) {
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if (length < 0) {
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throw new RangeError("BitVector length must increase by a nonnegative number.");
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}
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this.length += length;
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//add in new data
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}
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/** Creates a string version of the bit vector
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/** Creates a string version of the bit vector in B64. Does not keep the order of elements a sensible human readable format.
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*
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* @returns A bit vector in string format
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*/
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@ -226,26 +274,7 @@ Base64 = (function () {
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return "";
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}
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let bitstr = "";
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//extract bits from first uint32 - may not be all 32 bits
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let length_first = this.length % 32;
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let curr = this.bits[0];
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for (let i = 0; i < length_first; ++i) {
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bitstr = (curr % 2 == 0 ? '0' : '1') + bitstr;
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curr >>= 1;
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}
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//extract bits from rest of uint32s - always all 32 bits
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for (let i = 1; i < this.bits.length; ++i) {
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curr = this.bits[i];
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for (let j = 0; j < 32; ++j) {
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bitstr = (curr % 2 == 0 ? '0' : '1') + bitstr;
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curr >>= 1;
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}
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}
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//return the formed bitstring
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return bitstr;
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}
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};
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