API

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int GBase64 and deltaRLE

A compact way to represent signed integers and arrays of integers in URL friendly string format.

JavaScript Demo

var data = [1387901778, 1387901781, 1387901784, 1387901787,
1387901790, 1387901793, 1387901796, 1387901799, 1387901802,
1387901805, 1387901808, 1387901811, 1387901814, 1387901817,
1387901820, 1387901823, 1387901826, 1387901829, 1387901832,
1387901835, 1387901838, 1387901841, 1387901844, 1387901847,
1387901850, 1387901853, 1387901856, 1387901859, 1387901862,
1387901865, 1387901868];

console.log( deltaRLE( data ) ); // outputs: "1iKrdi$u3"

JavaScript implementation

var mapGBase64 = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ()",
	mapGBase64Index = mapGBase64.slice('');

function intToGBase64(num)
{
	var sign, str = '';

	if ( num < 0 ) {
		num = -num;
		sign = "-";
	} else {
		sign = '';
	}

	do {
		str = mapGBase64.charAt(num & 0x3f) + str;
		num = Math.floor(num / 64);
	} while (num);

	return sign + str;
}

function gBase64ToInt(str)
{
       var start, sign, num = 0;

       if ( str.charAt(0) == "-" ) {
               sign = -1;
               start = 1;
       } else {
               sign = 1;
               start = 0;
       }

       var pwr = Math.pow(2, (str.length - start - 1) * 6);
       for(var i = start; i < str.length; i++)
       {
               num += mapGBase64Index.indexOf(str.charAt(i)) * pwr;
               pwr = pwr / 64;
       }
       return sign * num;
}

// Compress array with Delta and RLE
//
function deltaRLE(data) {
	var rle = 0, times, dif, lastDif = null, last, res = '', lastRes;
	for (var i in data) {
		if ( !parseInt(i) ) {
			res += intToGBase64(data[i]);
		} else {
			dif = data[i] - last;
			// if ( ( parseInt(i) > 1 ) && ( lastDif == dif ) && ( rle < 63 ) ) // without ===
			if ( ( lastDif === dif ) && ( rle < 63 ) )
			{
				rle++;
				times = intToGBase64(rle);
				res = lastRes
					+ ( ( dif == 0 )
						? "*" + times
						: ( dif > 0
							? "$" + times + intToGBase64(dif)
							: "_" + times + intToGBase64(-dif) ) );
			} else {
				lastDif = dif;
				rle = 1;
				lastRes = res;
				res += ( dif == 0 )
					? "."
					: ( dif > 0
						? ":" + intToGBase64(dif)
						: "!" + intToGBase64(-dif) );
			}
		}
		last = data[i];
	}
	return res;
}

PHP partial implementation

Note:If it is to be ported in a language or system that does not support 64bit bitwise operators use the Javascript version which is more 64bit friendly.

function gBase64ToInt($str)
{
	$mapBase64 = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ()";

	if ( $str[0] == "-" ) {
		$sign = -1;
		$start = 1;
	} else {
		$sign = 1;
		$start = 0;
	}

	$num = 0;
	$pwr = (strlen($str) - $start - 1) * 6;
	for($i = $start; $i < strlen($str); $i++)
	{
		$num += strrpos($mapBase64, $str[$i]) * (1 << $pwr);
		$pwr = $pwr - 6;
	}
	return $sign * $num;
}