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    <p>Let's consider two solutions.</p> <h1>Base 32</h1> <p>For fun, let's consider using base-32 numbers. Yes, you can do that in JavaScript.</p> <p>First pack four 7-bit values into one integer:</p> <pre><code>function pack(a1,a2,a3,a4){ return ((a1 &lt;&lt; 8 | a2) &lt;&lt; 8 | a3) &lt;&lt; 8 | a4; } </code></pre> <p>Now, convert to base 32.</p> <pre><code>function encode(n){ var str = "000000" + n.toString(32); str = str.slice(0,6); return str; } </code></pre> <p>That should be not more than six digits. We make sure it's exactly six.</p> <p>Going the other direction:</p> <pre><code>function decode(s){ return parseInt(s, 32); } function unpack(x){ var a1 = x &amp; 0xff0000&gt;&gt;24, a2 = x &amp; 0x00ff0000&gt;&gt;16, a3 = x &amp; 0x0000ff00&gt;&gt;8, a4 = x &amp; 0x000000ff; return [a1, a2, a3, a4]; } </code></pre> <p>All that remains is to wrap the logic around this to handle the 6000 elements. To compress:</p> <pre><code>function compress(elts){ var str = ''; for(var i = 0; i &lt; elts.length; i+=4){ str += encode(pack(elts[i], elts[i+1], elts[i+2], elts[i+3]) } return str; } </code></pre> <p>And to uncompress:</p> <pre><code>function uncompress(str){ var elts = []; for(var i = 0; i &lt; str.length; i+=6){ elts = elts.concat(unpack(decode(str.slice(i, i+6))); } return elts; } </code></pre> <p>If you concatenate the results for all 6,000 elements, you'll have 1,500 packed numbers, which at six characters each will turn into about 9K. It's about 1.5 bytes per 7-bit value. It's by no means the information-theoretic maximum compression, but it's not that bad. To decode simply reverse the process:</p> <h1>Unicode</h1> <p>First we'll pack two 7-bit values into one integer:</p> <pre><code>function pack(a1,a2){ return (a1 &lt;&lt; 8 | a2) &lt;&lt; 8; } </code></pre> <p>We'll do this for all 6,000 inputs, then use our friend <code>String.fromCharCode</code> to turn all 3,000 values into a 3,000-character Unicode string:</p> <pre><code>function compress(elts){ var packeds = []; for (var i = 0; i &lt; elts.length; i+=2) { packeds.push(pack(elts[i], elts[i+1]); } return String.fromCharCode.apply(0, packeds); } </code></pre> <p>Coming back the other way, it's quite easy:</p> <pre><code>function uncompress(str) { var elts = [], code; for (var i = 0; i &lt; str.length; i++) { code=str.charCodeAt(i); elts.push(code&gt;&gt;8, code &amp; 0xff); } return elts; } </code></pre> <p>This will take up two bytes per two 7-bit values, so about 33% more efficient than the base 32 approach.</p> <p>If the above string is going to be written out into a script tag as a Javascript assignment such as <code>var data="HUGE UNICODE STRING";</code>, then quotation marks in string will need to be escaped:</p> <pre><code>javascript_assignment = 'var data = "' + compress(elts).replace(/"/g,'\\"') + '";'; </code></pre> <p>The above code is not meant to be production, and in particular does not handle edge cases where the the number of inputs is not a multiple of four or two.</p>
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