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how to convert javascript BigInt to Uint8Array with negative values considered

I have a java backend that's reading/writing arbitrary precision numbers with javascript front-end using bytes.
On Java side I just do:
new BigInteger("123").toByteArray()
The doc says:
Returns a byte array containing the two's-complement
representation of this BigInteger.
On javascript side I need to read the bytes into javascript's BigInt, and vise versa.
I have the javascript reading the bytes into BigInt as bellow:
const hex = Buffer.from(bytes).toString('hex')
let big = BigInt('0x' + hex)
if (a[0] & 0x80) {
const negative = BigInt('0x1' + '0'.repeat(hex.length))
big -= negative
}
But converting BigInt to bytes seems to be very tricky. I looked around and found that other solutions all only cover positive numbers but not negative numbers

After digging around and understanding two's-complement representation, I'm answering my own question:
const big0 = BigInt(0)
const big1 = BigInt(1)
const big8 = BigInt(8)
function bigToUint8Array(big: bigint) {
if (big < big0) {
// work out how long is the big int in bits and add 1
const bits: bigint = (BigInt(big.toString(2).length) / big8 + big1) * big8
// create a BigInt that's 100000... of length of big + 1
const prefix1: bigint = big1 << bits
big += prefix1
}
let hex = big.toString(16)
if (hex.length % 2) {
hex = '0' + hex
}
const len = hex.length / 2
const u8 = new Uint8Array(len)
var i = 0
var j = 0
while (i < len) {
u8[i] = parseInt(hex.slice(j, j + 2), 16)
i += 1
j += 2
}
return u8
}

Make a utf-8 string shorter with a utf-32 encoding in Javascript?

I'm trying to find a way to compress/decompress a string in Javascript. By compress I mean to make the string look shorter (less char). That's my goal.
Here's an example of how things should work:
// The string that I want to make shorter
// It will only contain [a-zA-Z0-9] chars and some ponctuations like ()[]{}.,;'"!
var string = "I like bananas !";
// The compressed string, maybe something like "䐓㐛꯱字",
// which is shorter than the original
var shortString = compress(string);
// The original string, "I like banana !"
var originalString = decompress(shortString);
Here's my first idea (maybe there's a better way to get to my goal, and if so I'm interested in it).
I know that my original string will be in utf-8. So I'm thinking of using utf-32 for the encoding, which should divide by 4 the length of the string.
But I don't know how to do these 2 functions that construct new strings with different encoding. Here's the code I have so far that doesn't work...
function compress(string) {
string = unescape(encodeURIComponent(string));
var newString = '';
for (var i = 0; i < string.length; i++) {
var char = string.charCodeAt(i);
newString += parseInt(char, 8).toString(32);
}
return newString;
}

Since you're using a set of less than 100 characters and that javascript strings are encoded in UTF-16 (which mean you have 65536 possible characters), what you can do is concatenate the character codes so as to have one "compressed" character per two basic character. This allows you to compress strings to half the length.
Like this for example:
document.getElementById('compressBtn').addEventListener('click', function() {
var stringToCompress = document.getElementById('tocompress').value;
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);
if (stringToCompress === decompressedString) {
document.getElementById('display').innerHTML = stringToCompress + ", length of " + stringToCompress.length  + " characters compressed to " + compressedString + ", length of " + compressedString.length + " characters back to " + decompressedString;
} else {
document.getElementById('display').innerHTML = "This string cannot be compressed"
}
})
function compress(string) {
string = unescape(encodeURIComponent(string));
var newString = '',
char, nextChar, combinedCharCode;
for (var i = 0; i < string.length; i += 2) {
char = string.charCodeAt(i);
if ((i + 1) < string.length) {
// You need to make sure that you don't have 3 digits second character else you might go over 65536.
// But in UTF-16 the 32 characters aren't in your basic character set. But it's a limitation, anything
// under charCode 32 will cause an error
nextChar = string.charCodeAt(i + 1) - 31;
// this is to pad the result, because you could have a code that is single digit, which would make
// decompression a bit harder
combinedCharCode = char + "" + nextChar.toLocaleString('en', {
minimumIntegerDigits: 2
});
// You take the concanated code string and convert it back to a number, then a character
newString += String.fromCharCode(parseInt(combinedCharCode, 10));
} else {
// Here because you won't always have pair number length
newString += string.charAt(i);
}
}
return newString;
}
function decompress(string) {
var newString = '',
char, codeStr, firstCharCode, lastCharCode;
for (var i = 0; i < string.length; i++) {
char = string.charCodeAt(i);
if (char > 132) {
codeStr = char.toString(10);
// You take the first part of the compressed char code, it's your first letter
firstCharCode = parseInt(codeStr.substring(0, codeStr.length - 2), 10);
// For the second one you need to add 31 back.
lastCharCode = parseInt(codeStr.substring(codeStr.length - 2, codeStr.length), 10) + 31;
// You put back the 2 characters you had originally
newString += String.fromCharCode(firstCharCode) + String.fromCharCode(lastCharCode);
} else {
newString += string.charAt(i);
}
}
return newString;
}
var stringToCompress = 'I like bananas!';
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);
document.getElementById('display').innerHTML = stringToCompress + ", length of " + stringToCompress.length  + " characters compressed to " + compressedString + ", length of " + compressedString.length + " characters back to " + decompressedString;
body {
padding: 10px;
}
#tocompress {
width: 200px;
}
<input id="tocompress" placeholder="enter string to compress" />
<button id="compressBtn">
Compress input
</button>
<div id="display">
</div>
Regarding the possible use of UTF-32 to further compress, I'm not sure it's possible, I might be wrong on that, but from my understanding it's not feasible. Here's why:
The approach above is basically concatenating two 1 byte values in one 2 bytes value. This is possible because javascript strings are encoded in 2 bytes (or 16 bits) (note that from what I understand the engine could decide to store differently making this compression unnecessary from a purely memory space point of view - that being said, in the end, one character is considered being 16 bits). A cleaner way to make the compression above would in fact to user the binary numbers instead of the decimal, it would make much more sense. Like this for example:
document.getElementById('compressBtn').addEventListener('click', function() {
var stringToCompress = document.getElementById('tocompress').value;
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);
if (stringToCompress === decompressedString) {
document.getElementById('display').innerHTML = stringToCompress + ", length of " + stringToCompress.length + " characters compressed to " + compressedString + ", length of " + compressedString.length + " characters back to " + decompressedString;
} else {
document.getElementById('display').innerHTML = "This string cannot be compressed"
}
})
function compress(string) {
string = unescape(encodeURIComponent(string));
var newString = '',
char, nextChar, combinedCharCode;
for (var i = 0; i < string.length; i += 2) {
// convert to binary instead of keeping the decimal
char = string.charCodeAt(i).toString(2);
if ((i + 1) < string.length) {
nextChar = string.charCodeAt(i + 1).toString(2) ;
// you still need padding, see this answer https://stackoverflow.com/questions/27641812/way-to-add-leading-zeroes-to-binary-string-in-javascript
combinedCharCode = "0000000".substr(char.length) + char + "" + "0000000".substr(nextChar.length) + nextChar;
// You take the concanated code string and convert it back to a binary number, then a character
newString += String.fromCharCode(parseInt(combinedCharCode, 2));
} else {
// Here because you won't always have pair number length
newString += string.charAt(i);
}
}
return newString;
}
function decompress(string) {
var newString = '',
char, codeStr, firstCharCode, lastCharCode;
for (var i = 0; i < string.length; i++) {
char = string.charCodeAt(i);
if (char > 132) {
codeStr = char.toString(2);
// You take the first part (the first byte) of the compressed char code, it's your first letter
firstCharCode = parseInt(codeStr.substring(0, codeStr.length - 7), 2);
// then the second byte
lastCharCode = parseInt(codeStr.substring(codeStr.length - 7, codeStr.length), 2);
// You put back the 2 characters you had originally
newString += String.fromCharCode(firstCharCode) + String.fromCharCode(lastCharCode);
} else {
newString += string.charAt(i);
}
}
return newString;
}
var stringToCompress = 'I like bananas!';
var compressedString = compress(stringToCompress);
var decompressedString = decompress(compressedString);
document.getElementById('display').innerHTML = stringToCompress + ", length of " + stringToCompress.length + " characters compressed to " + compressedString + ", length of " + compressedString.length + " characters back to " + decompressedString;
<input id="tocompress" placeholder="enter string to compress" />
<button id="compressBtn">
Compress input
</button>
<div id="display">
</div>
So why not push the logic and use utf-32, which should be 4 bytes, meaning four 1 byte characters. One problem is that javascript has 2 bytes string. It's true that you can use pairs of 16 bits characters to represent utf-32 characters. Like this:
document.getElementById('test').innerHTML = "\uD834\uDD1E";
<div id="test"></div>
But if you test the length of the resulting string, you'll see that it's 2, even if there's only one "character". So from a javascript perspective, you're not reducing the actual string length.
The other thing is that UTF-32 has in fact 221 characters. See here: https://en.wikipedia.org/wiki/UTF-32
It is a protocol to encode Unicode code points that uses exactly 32
bits per Unicode code point (but a number of leading bits must be zero
as there are fewer than 221 Unicode code points)
So you don't really have 4 bytes, in fact you don't even have 3, which would be needed to encode 3. So UTF-32 doesn't seem to be a way to compress even more. And since javascript has native 2 bytes strings, it seems to me to be the most efficient - using that approach at least.

If your strings only contain ASCII characters [0, 127] you can "compress" the string using a custom 6 or 7-bit code page.
You can do this several ways, but I think one of the simpler methods is to define an array holding all allowed characters - a LUT, lookup-table if you like, then use its index value as the encoded value. You would of course have to manually mask and shift the encoded value into a typed array.
If your LUT looked like this:
var lut = " abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.,:;!(){}";
you would in this case deal with a LUT of length 71 which means we would need to use a 7-bit range or [0, 127] (if length were 64 we could've reduced the it to 6-bit [0, 63] values).
Then you would take each characters in the string and convert to index values (you would normally do all the following steps in a single operation but I have separated them for simplicity):
var lut = " abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.,:;!(){}";
var str = "I like bananas !";
var page = [];
Array.prototype.forEach.call(str, function(ch) {
var i = lut.indexOf(ch);
if (i < 0) throw "Invalid character - can't encode";
page.push(i);
});
console.log("Intermediate page:", page);
You can always tweak the LUT so that the most used characters are in the beginning, then support variable encoding bit-range, find max value and use that to determine what range you want to encode in. You can add an initial bit as a flag as to which range the encoding uses (for example bit 0 set if 6-bit fits, otherwise use 7-bit range).
Now that you know the indices we can start to encode the binary output itself using a 7-bit approach. Since JavaScript only support byte values, i.e. 8-bit width, we have to do all the split, shift and merge operations manually.
This means we need to keep track of remainder and position on a bit-level.
Say first index value was the following 7-bit value (full 7-bit range for readability - all in pseudo format):
&b01111111
The first step would be to shift it over to bit position 0 and keep track of a remainder:
&b01111111 << 1
Resulting in:
&b11111110
^
new bit position: 7
new remainder : 1
Then the next index value, for example:
&b01010101
would be encoded like this - first convert to 7-bit value in its own byte representation:
&b01010101 << 1 => &b10101010
Then get the reminder part first. To obtain this will shift everything right-wise using 8-bit minus the current remainder (within modulo of 8):
remainderValue = &b10101010 >>> (8 - remainder)
leaving us with the following representation:
&b00000001
(Note that we use triple >>> to shift right to avoid issues with sign.)
Next step now is to merge this value with our previous value that has already been encoded and stored into our destination byte array - for this we'll use an OR operation:
Index 0 New value Result in index 0 (index of dst. array)
&b11111110 | &b00000001 => &b11111111
then go to next index in our destination array and store the rest of the current value, then update the remainder and position.
The "leftover" of the byte is calculated like this using the original (after shifting it) 7-bit byte value:
leftover = &b10101010 << remainder => &b01010100
which we now put into the next position:
Index 0 Index 1 (destination array index, not page index)
&b11111111 01010100
^
new bit position: 14
new remainder : 2
And so on with the remaining index values. See this answer for actual code on how you can do this in JavaScript - the code in this answer doesn't deal with string encoding per-se, but it shows how you can shift byte buffers bit-wise which is essentially the same you need for this task.
To calculate the remainder step, use 8-bits minus your custom bit-range:
step = 8 - newRange (here 7) => 1
This will also be the start remainder. For each character, you'll add the step to remainder after it has been processed, but remember to use modulo 8 (byte width) when you use it for shifting:
remainder += step;
numOfBitsToShift = remainder % 8;
Bit-position uses of course the bit-range, in this case 7:
bitPosition += 7;
Then to find which indices you're dealing with you divide the bitPosition on 8, if any decimal you have to deal with two indexes (old and new), if no decimal the current position represents new index only (only shift is needed for current index value).
You can also use modulo and when modulo of remainder = step you know you that you are dealing with a single index in the destination.
To calculate the final length you would use the bit-length and length of string, then ceil the result so that all characters will fit into a 8-byte byte array which is the only array we can get in JavaScript:
dstLength = Math.ceil(7 * str.length / 8);
To decode you just reverse all the steps.
An alternative, if you use long strings or have to move forward fast, is to use an established compressor such as zlib which has a very compact header as well as good performance in JavaScript in the case of the linked solution. This will also deal with "patterns" in the string to further optimize the resulting size.
Disclaimer: as this is mostly a theoretical answer there might be some errors. Feel free to comment if any are found. Refer to linked answer for actual code example.

for full code see here: https://repl.it/NyMl/1
using the Uint8Array you can work with the bytes.
let msg = "This is some message";
let data = []
for(let i = 0; i < msg.length; ++i){
data[i] = msg.charCodeAt(i);
}
let i8 = new Uint8Array(data);
let i16 = new Uint16Array(i8.buffer);
you could also think of a compression like this: http://pieroxy.net/blog/pages/lz-string/demo.html
if you don't want to use a 3rd party library, the lz based compression should be fairly simple. see here (wikipedia)

I use the same library mentioned above, lz-string https://github.com/pieroxy/lz-string, and it creates file sizes that are smaller than most of the binary formats like Protocol Buffers.
I compress via Node.js like this:
var compressedString = LZString.compressToUTF16(str);
And I decompress client side like this:
var decompressedString = LZString.decompressFromUTF16(str);

Var overflow in JS and mongo [duplicate]

In JavaScript I would like to create the binary hash of a large boolean array (54 elements) with the following method:
function bhash(arr) {
for (var i = 0, L = arr.length, sum = 0; i < L; sum += Math.pow(2,i)*arr[i++]);
return sum;
}
In short: it creates the smallest integer to store an array of booleans in. Now my problem is that javascript apparently uses floats as default. The maximum number I have to create is 2^54-1 but once javascript reaches 2^53 it starts doing weird things:
9007199254740992+1 = 9007199254740994
Is there any way of using integers instead of floats in javascript? Or large integer summations?

JavaScript uses floating point internally.
What is JavaScript's highest integer value that a number can go to without losing precision?
In other words you can't use more than 53 bits. In some implementations you may be limited to 31.
Try storing the bits in more than one variable, use a string, or get a bignum library, or if you only need to deal with integers, a biginteger library.

BigInt is being added as a native feature of JavaScript.
typeof 123;
// → 'number'
typeof 123n;
// → 'bigint'
Example:
const max = BigInt(Number.MAX_SAFE_INTEGER);
const two = 2n;
const result = max + two;
console.log(result);
// → '9007199254740993'

javascript now has experimental support for BigInt.
At the time of writing only chrome supports this.
caniuse has no entry yet.
BigInt can be either used with a constructor, e.g. BigInt(20) or by appending n, e.g. 20n
Example:
const max = Number.MAX_SAFE_INTEGER;
console.log('javascript Number limit reached', max + 1 === max + 2) // true;
console.log('javascript BigInt limit reached', BigInt(max) + 1n === BigInt(max) + 2n); // false

No. Javascript only has one numeric type. You've to code yourself or use a large integer library (and you cannot even overload arithmetic operators).
Update
This was true in 2010... now (2019) a BigInt library is being standardized and will most probably soon arrive natively in Javascript and it will be the second numeric type present (there are typed arrays, but - at least formally - values extracted from them are still double-precision floating point numbers).

Another implementation of large integer arithmetic (also using BigInt.js) is available at www.javascripter.net/math/calculators/100digitbigintcalculator.htm. Supports the operations + - * / as well as remainder, GCD, LCM, factorial, primality test, next prime, previous prime.

So while attempting one of the leetcode problem I have written a function which takes two numbers in form of string and returns the sum of those numbers in form of string.
(This doesn't work with negative numbers though we can modify this function to cover that)
var addTwoStr = function (s1, s2) {
s1 = s1.split("").reverse().join("")
s2 = s2.split("").reverse().join("")
var carry = 0, rS = '', x = null
if (s1.length > s2.length) {
for (let i = 0; i < s1.length; i++) {
let s = s1[i]
if (i < s2.length) {
x = Number(s) + Number(s2[i]) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
if (carry) {
x = Number(s) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
rS += s
}
}
}
} else {
for (let i = 0; i < s2.length; i++) {
let s = s2[i]
if (i < s1.length) {
x = Number(s) + Number(s1[i]) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
if (carry) {
x = Number(s) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
rS += s
}
}
}
}
if (carry) {
rS += String(carry)
}
return rS.split("").reverse().join("")
}
Example: addTwoStr('120354566', '321442535')
Output: "441797101"

There are various BigInteger Javascript libraries that you can find through googling. e.g. http://www.leemon.com/crypto/BigInt.html

Here's (yet another) wrapper around Leemon Baird's BigInt.js
It is used in this online demo of a big integer calculator in JavaScript which implements the usual four operations + - * /, the modulus (%), and four builtin functions : the square root (sqrt), the power (pow), the recursive factorial (fact) and a memoizing Fibonacci (fibo).

You're probably running into a byte length limit on your system. I'd take the array of booleans, convert it to an array of binary digits ([true, false, true] => [1,0,1]), then join this array into a string "101", then use parseInt('101',2), and you'll have your answer.

/** --if you want to show a big int as your wish use install and require this module
* By using 'big-integer' module is easier to use and handling the big int numbers than regular javascript
* https://www.npmjs.com/package/big-integer
*/
let bigInt = require('big-integer');
//variable: get_bigInt
let get_bigInt = bigInt("999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999");
let arr = [1, 100000, 21, 30, 4, BigInt(999999999999), get_bigInt.value];
console.log(arr[6]); // Output: 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999n
//Calculation
console.log(arr[6] + 1n); // +1
console.log(arr[6] + 100n); // +100
console.log(arr[6] - 1n); // -1
console.log(arr[6] - 10245n); // -1000n
console.log((arr[6] * 10000n) + 145n - 435n);

JavaScript: Read 8 bytes to 64 bit integer

I have a buffer object which contains eight bytes. These eight bytes should now be interpreted as 64 bit integer.
Currently I use following algorithm:
var int = buff[0];
for (var i = 1; i < buff.length; i++) {
int += (buff[i] * Math.pow(2, 8 * i));
}
console.log(int);
this works but I believe there are better ways (maybe using Uint64Array).
Unfortunately I cannot find how a Uint16Array could help me here for.
Regards
Update:
// puts two 32bit integers to one 64bit integer
var bufInt = (buf.readUInt32BE(0) << 8) + buf.readUInt32BE(4);

Javascript does not support 64 bit integers, because the native number type is a 64-bit double, giving only 53 bits of integer range.
You can create arrays of 32-bit numbers (i.e. Uint32Array) but if there were a 64-bit version of those there'd be no way to copy values from it into standalone variables.

Since the latest Node.js v12.0.0, you can now use buf.readBigUInt64LE :))

You can use node-int64 for 64-bit integer support:
var Int64 = require('node-int64');
var int64 = new Int64(buff);

As javascript dont support 64bit integer readily,here is one solution that worked for me.Here i am converting 8 Byte unix timestamp.
inputString = "0000016b40d8ea30"
var buf = Buffer.from(inputString, 'hex');
timestamp = (parseInt(buf.toString("hex"),16).toString());
console.log(timestamp); //1560161086000

For a pity, correct answer is that Javascript not supports 64 bit integers (till now).
So, trying to get exact 64bit integer stored into your 8 bytes into single JS number-type variable will fail. Anyway.
Some decisions:
Exact bits from 0 to 52:
If you do not need upper 11 bits of 64bit and it's enought for you to deal with exact 53-bit integers, you can use this way:
// puts up to 53 bits by 32bit integers to one "64bit" integer
var bufInt = (buf.readUInt32BE(0) & 0x001FFFFF) * 4294967296 + buf.readUInt32BE(4);
(edited question)
"64bit" int with possible loose of low 11 bit correct states:
Otherwise, if you need "common big value" of 64bit and you don't interest about exact values of till 11 low bits (rightmost 2-3 digits of huge 64bit value), you can use this way:
// puts 64 bit value by 32bit integers to one "64bit" integer
// with possible loose of lower 11 bits correctness
var bufInt = buf.readUInt32BE(0) * 4294967296 + buf.readUInt32BE(4);
For those who interest int64 (64 bit integers support) in Javascript, BEWARE!
Look:
var x1 = 1 << 30;
var x2 = 1 << 31;
var x3 = 1 << 32;
var x4 = 1 << 33;
var a = 1240611072103715194;
var b = 1240611072103715193;
var c = 1240611072103700000;
alert(''
+ 'x1=' + x1 + ' (should =1073741824)\n'
+ 'x2=' + x2 + ' (should =2147483648)\n'
+ 'x3=' + x3 + ' (should =4294967296)\n'
+ 'x4=' + x4 + ' (should =8589934592)\n'
+ 'a=' + a + ' (should =1240611072103715194)\n'
+ 'a-b=' + (a-b) + ' (should =1)\n'
+ 'a-c=' + (a-c) + ' (should =15194)\n'
);
RESULT:
x1=1073741824 (should =1073741824)
x2=-2147483648 (should =2147483648)
x3=1 (should =4294967296)
x4=2 (should =8589934592)
a=1240611072103715000 (should =1240611072103715194)
a-b=0 (should =1)
a-c=15104 (should =15194)

There are some modules around to provide 64bit integer support:
node-bigint
bignum (based on OpenSSL)
Maybe your problem can be solved using one of those libraries.

compress/urlencode a series of 100 base-4 numbers in javascript

First thing: must be done entirely in javascript. (JQuery/mootools optional)
I have a series of 100 numbers each set 0,1,2, or 3 - these represents settings on the page. I would like to encode these to the shortest string possible to create a permalink to the page.
I am thinking the best way would be to store them in binary couplets, convert those couplets to a string, ant then urlencode the string.
However the best I have found so far is parseint( binary_var, 2 ), which coverts a binary number to a base_10 number. However to get the string short enough I'll need a better system.
If I could convert to 64-bit encoding I could store all the data in just 4 chars, I think. I know urls support unicode now, and I believe I can use escape and unescape to encode/decode 64-bit chars, so the main thing I am looking for is a way to encode/decode binary data to 64-bit characters.
Of course I am not 100% sure this is the best way, or will even work, so it I am completely off track feel free to point me in the right direction.
Thanks!

You can encode such arrays of numbers into a string, 3 per character, like this:
function encodeBase4(base4) {
var i, rv = [], n = ~~((base4.length + 2) / 3) * 3;
for (i = 0; i < n; i += 3) {
rv.push(
32 +
((base4[i] || 0) & 3) +
((base4[i + 1] || 0) & 3) * 4 +
((base4[i + 2] || 0) & 3) * 16
);
}
return String.fromCharCode.apply(null, rv);
}
You can then convert the other direction like this:
function decodeBase4(str) {
var i, rv = [], n = str.length;
for (i = 0; i < n; ++i) {
var b = str.charCodeAt(i) - 32;
rv.push(b & 3);
rv.push(~~(b / 4) & 3);
rv.push(~~(b / 16) & 3);
}
return rv;
}
Here's the jsfiddle which seems to work on its simple test case. (Note that you end up with a list that's a multiple of 3 in length; you'd have to know how many real values there are and just ignore the zeros at the end.)
Now these result strings will be "dirty" and require URL encoding if you're putting them in URLs. If you packed only 2 numbers per character, you could make the resulting strings be all alphabetic, and thus you'd avoid the encoding penalty; however they'd be longer, of course.

100 pieces of information with 2 bits each require 200 bits in total. With base 64 encoding you would require ceil(200/log2(64)) = 34 characters.
A URI path segment allows 79 character that don’t require being encoded using the percent-encoding. If you add the path segment separator / you have 80 characters and thus require ceil(200/log2(80)) = 32 characters. That’s the optimum you can achieve using the path alone.
You could use more than these characters, even Unicode characters. But those would need to be encoded with the percent-encoding as URIs are only allowed to contain US-ASCII. A URI path like /ä (ä = U+00E4) is actually /%C3%A4 and only the browser displays it as /ä.
Here’s an example (functions taken from arbitrary base conversion in javascript):
function getValueOfDigit(digit, alphabet)
{
var pos = alphabet.indexOf(digit);
return pos;
}
function convert(src, srcAlphabet, dstAlphabet)
{
var srcBase = srcAlphabet.length;
var dstBase = dstAlphabet.length;
var wet = src;
var val = 0;
var mlt = 1;
while (wet.length > 0)
{
var digit = wet.charAt(wet.length - 1);
val += mlt * getValueOfDigit(digit, srcAlphabet);
wet = wet.substring(0, wet.length - 1);
mlt *= srcBase;
}
wet = val;
var ret = "";
while (wet >= dstBase)
{
var digitVal = wet % dstBase;
var digit = dstAlphabet.charAt(digitVal);
ret = digit + ret;
wet /= dstBase;
}
var digit = dstAlphabet.charAt(wet);
ret = digit + ret;
return ret;
}
var base4Alphabet = "0123",
base79Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~!$&'()*+,;=:#",
base80Alphabet = base79Alphabet+"/";
alert(convert(getValueOfDigit("010203210", base4Alphabet), base4Alphabet, base80Alphabet)); // "C#Q"