Archive for March, 2010

Large Binary Numbers in Javascript

21st March
2010
written by admin

Have you ever wondered what the largest number is?  At one point it was a googolplex, but unless you write a custom class to deal with really large numbers, your dev environment will never count to a googolplex.

For http://loc.is I am reworking a geohash encoding algorithm today, and I wanted to see what Javascript could handle.  Strongly typed languages like Java have known upper limits, but languages like javascript are a bit more mysterious, so the only way to know is to find out.  I wrote this function to test it, and I ran it in the firebug console on a random webpage ( firebug won’t work unless the DOM is ready ).



for( i = 0 ; i < 500 ; i++){
var value = Math.pow(2,i) +1;
console.log (   i + "\n" +
value + "\n" +
value.toString(2));
}

The output finally looks like this, and reveals that 2^52 is the largest number you can add 1 to and still represent it as an integer. Any larger and javascript will just use it as a float, and you will not have a sufficient number of bits to represent it.  I wonder if this is the same in all browser/ os combination pairs?

51
2251799813685249
1000000000000000000000000000000000000000000000000001

52
4503599627370497
10000000000000000000000000000000000000000000000000001

53
9007199254740992
100000000000000000000000000000000000000000000000000000

54
18014398509481984
1000000000000000000000000000000000000000000000000000000

So in this circumstance, javascript seems to have 54 bits of integer accuracy, a few short of a LONG 64 bit int, or IEEE 80 bit notation.


Test it yourself, and let me know.
0 Comments
Uncategorized

New jEdit Syntax Edit Modes for Perl+HTML & XML+CDATA + HTML

5th March
2010
written by admin

I love my syntax highlighting in jEdit, and why shouldn’t I?  Good Syntax Highlighting helps you catch code errors early.  So about 2 years ago, I created a custom jEdit “Edit Mode” so that HTML buried in your XML CDATA tags would be Syntax Highlighted.  Here is the original post on Google Groups ( http://groups.google.com/group/opensocial-api/browse_thread/thread/12e250246ab64054/343c858695e8eb12 ).

Here is the custom Edit Mode for XML->CDATA->HTML c-xml.xml

It uses a simple trick to identify the CDATA with HTML with a special CDATA tag like the one below

<![CDATA[<!--HTML-->  
<html>
<!-- friendly neighborhood web page -->
</html>
]]>

The perl version is here perl-html.xml

So for the perl version i use the structure of Perl’s HEREDOCS and use the following java capable regex

<<\p{Space}*(['"])([\p{Space}\p{Alnum}]*)\1;?\s*<\!--.*HTML.*-->

Which will HTML Syntax highlight any perl HEREDOC as HTML if it has <!– HTML –> in it so the following should syntax highlight.  There is however, one bug.  If your HEREDOC is not well formed, meaning you have an unclosed tag css object, or  javascript call, then the syntax highlighting gets stuck.  Maybe I will figure out how to make this work for non well-formed HTML.  any ideas?

print <<"EOT"; <!-- HTML -->
<html>
<!-- friendly neighborhood web page -->
</html>
EOT
0 Comments
Uncategorized