Merge branch 'sock_encoding' into atree_encode

js/utils.js

@@ -74,6 +74,8 @@ function log(b, n) {
 // https://stackoverflow.com/a/27696695
 // Modified for fixed precision
 
+// Base64.fromInt(-2147483648); // gives "200000"
+// Base64.toInt("200000"); // gives -2147483648
 Base64 = (function () {
     var digitsStr =
     //   0       8       16      24      32      40      48      56     63
@@ -125,8 +127,246 @@ Base64 = (function () {
     };
 })();
 
-// Base64.fromInt(-2147483648); // gives "200000"
+
-// Base64.toInt("200000"); // gives -2147483648
+/** A class used to represent an arbitrary length bit vector. Very useful for encoding and decoding.
+ *
+ */
+ class BitVector {
+
+    /** Constructs an arbitrary-length bit vector.
+     * @class
+     * @param {String | Number} data - The data to append.
+     * @param {Number} length - A set length for the data. Ignored if data is a string.
+     *
+     * The structure of the Uint32Array should be [[last, ..., first], ..., [last, ..., first], [empty space, last, ..., first]]
+     */
+    constructor(data, length) {
+        let bit_vec = [];
+
+        if (typeof data === "string") {
+            let int = 0;
+            let bv_idx = 0;
+            length = data.length * 6;
+
+            for (let i = 0; i < data.length; i++) {
+                let char = Base64.toInt(data[i]);
+                let pre_pos = bv_idx % 32;
+                int |= (char << bv_idx);
+                bv_idx += 6;
+                let post_pos = bv_idx % 32;
+                if (post_pos < pre_pos) { //we have to have filled up the integer
+                    bit_vec.push(int);
+                    int = (char >>> (6 - post_pos));
+                }
+
+                if (i == data.length - 1 && post_pos != 0) {
+                    bit_vec.push(int);
+                }
+            }
+        } else if (typeof data === "number") {
+            if (typeof length === "undefined")
+            if (length < 0) {
+                throw new RangeError("BitVector must have nonnegative length.");
+            }
+
+            //convert to int just in case
+            data = Math.round(data);
+
+            //range of numbers that won't fit in a uint32
+            if (data > 2**32 - 1 || data < -(2 ** 32 - 1)) {
+                throw new RangeError("Numerical data has to fit within a 32-bit integer range to instantiate a BitVector.");
+            }
+            bit_vec.push(data);
+        } else {
+            throw new TypeError("BitVector must be instantiated with a Number or a B64 String");
+        }
+
+        this.length = length;
+        this.bits = new Uint32Array(bit_vec);
+    }
+
+    /** Return value of bit at index idx.
+     *
+     * @param {Number} idx - The index to read
+     *
+     * @returns The bit value at position idx
+     */
+    read_bit(idx) {
+        if (idx < 0 || idx >= this.length) {
+            throw new RangeError("Cannot read bit outside the range of the BitVector.");
+        }
+        return ((this.bits[Math.floor(idx / 32)] & (1 << (idx % 32))) == 0 ? 0 : 1);
+    }
+
+    /** Returns an integer value (if possible) made from the range of bits [start, end). Undefined behavior if the range to read is too big.
+     *
+     * @param {Number} start - The index to start slicing from. Inclusive.
+     * @param {Number} end - The index to end slicing at. Exclusive.
+     *
+     * @returns An integer representation of the sliced bits.
+     */
+    slice(start, end) {
+        //TO NOTE: JS shifting is ALWAYS in mod 32. a << b will do a << (b mod 32) implicitly.
+
+        if (end < start) {
+            throw new RangeError("Cannot slice a range where the end is before the start.");
+        } else if (end == start) {
+            return 0;
+        } else if (end - start > 32) {
+            //requesting a slice of longer than 32 bits (safe integer "length")
+            throw new RangeError("Cannot slice a range of longer than 32 bits (unsafe to store in an integer).");
+        }
+
+        let res = 0;
+        if (Math.floor((end - 1) / 32) == Math.floor(start / 32)) {
+            //the range is within 1 uint32 section - do some relatively fast bit twiddling
+            res = (this.bits[Math.floor(start / 32)] & ~((((~0) << ((end - 1))) << 1) | ~((~0) << (start)))) >>> (start % 32);
+        } else {
+            //the number of bits in the uint32s
+            let start_pos = (start % 32);
+            let int_idx = Math.floor(start/32);
+            res = (this.bits[int_idx] & ((~0) << (start))) >>> (start_pos);
+            res |= (this.bits[int_idx + 1] & ~((~0) << (end))) << (32 - start_pos);
+        }
+
+        return res;
+
+        // General code - slow
+        // for (let i = start; i < end; i++) {
+        //     res |= (get_bit(i) << (i - start));
+        // }
+    }
+
+    /** Assign bit at index idx to 1.
+     *
+     * @param {Number} idx - The index to set.
+     */
+    set_bit(idx) {
+        if (idx < 0 || idx >= this.length) {
+            throw new RangeError("Cannot set bit outside the range of the BitVector.");
+        }
+        this.bits[Math.floor(idx / 32)] |= (1 << idx % 32);
+    }
+
+    /** Assign bit at index idx to 0.
+     *
+     * @param {Number} idx - The index to clear.
+     */
+    clear_bit(idx) {
+        if (idx < 0 || idx >= this.length) {
+            throw new RangeError("Cannot clear bit outside the range of the BitVector.");
+        }
+        this.bits[Math.floor(idx / 32)] &= ~(1 << idx % 32);
+    }
+
+    /** Creates a string version of the bit vector in B64. Does not keep the order of elements a sensible human readable format.
+     *
+     * @returns A b64 string representation of the BitVector.
+     */
+    toB64() {
+        if (this.length == 0) {
+            return "";
+        }
+        let b64_str = "";
+        let i = 0;
+        while (i < this.length) {
+            b64_str += Base64.fromIntV(this.slice(i, i + 6), 1);
+            i += 6;
+        }
+
+        return b64_str;
+    }
+
+    /** Returns a BitVector in bitstring format. Probably only useful for dev debugging.
+     *
+     * @returns A bit string representation of the BitVector. Goes from higher-indexed bits to lower-indexed bits. (n ... 0)
+     */
+    toString() {
+        let ret_str = "";
+        for (let i = 0; i < this.length; i++) {
+            ret_str = (this.read_bit(i) == 0 ? "0": "1") + ret_str;
+        }
+        return ret_str;
+    }
+
+     /** Returns a BitVector in bitstring format. Probably only useful for dev debugging.
+     *
+     * @returns A bit string representation of the BitVector. Goes from lower-indexed bits to higher-indexed bits. (0 ... n)
+     */
+    toStringR() {
+        let ret_str = "";
+        for (let i = 0; i < this.length; i++) {
+            ret_str += (this.read_bit(i) == 0 ? "0": "1");
+        }
+        return ret_str;
+    }
+
+    /** Appends data to the BitVector.
+     *
+     * @param {Number | String} data - The data to append.
+     * @param {Number} length - The length, in bits, of the new data. This is ignored if data is a string.
+     */
+     append(data, length) {
+        if (length < 0) {
+            throw new RangeError("BitVector length must increase by a nonnegative number.");
+        }
+
+        let bit_vec = [];
+        for (const uint of this.bits) {
+            bit_vec.push(uint);
+        }
+        if (typeof data === "string") {
+            let int = bit_vec[bit_vec.length - 1];
+            let bv_idx = this.length;
+            length = data.length * 6;
+            let updated_curr = false;
+            for (let i = 0; i < data.length; i++) {
+                let char = Base64.toInt(data[i]);
+                let pre_pos = bv_idx % 32;
+                int |= (char << bv_idx);
+                bv_idx += 6;
+                let post_pos = bv_idx % 32;
+                if (post_pos < pre_pos) { //we have to have filled up the integer
+                    if (bit_vec.length == this.bits.length && !updated_curr) {
+                        bit_vec[bit_vec.length - 1] = int;
+                        updated_curr = true;
+                    } else {
+                        bit_vec.push(int);
+                    }
+                    int = (char >>> (6 - post_pos));
+                }
+
+                if (i == data.length - 1) {
+                    if (bit_vec.length == this.bits.length && !updated_curr) {
+                        bit_vec[bit_vec.length - 1] = int;
+                    } else if (post_pos != 0) {
+                        bit_vec.push(int);
+                    }
+                }
+            }
+        } else if (typeof data === "number") {
+            //convert to int just in case
+            let int = Math.round(data);
+
+            //range of numbers that "could" fit in a uint32 -> [0, 2^32) U [-2^31, 2^31)
+            if (data > 2**32 - 1 || data < -(2 ** 31)) {
+                throw new RangeError("Numerical data has to fit within a 32-bit integer range to instantiate a BitVector.");
+            }
+            //could be split between multiple new ints
+            //reminder that shifts implicitly mod 32
+            bit_vec[bit_vec.length - 1] |= ((int & ~((~0) << length)) << (this.length));
+            if (((this.length - 1) % 32 + 1) + length > 32) {
+                bit_vec.push(int >>> (32 - this.length));
+            }
+        } else {
+            throw new TypeError("BitVector must be appended with a Number or a B64 String");
+        }
+
+        this.bits = new Uint32Array(bit_vec);
+        this.length += length;
+    }
+};
+
 
 /*
     Turns a raw stat and a % stat into a final stat on the basis that - raw and >= 100% becomes 0 and + raw and <=-100% becomes negative.