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Message from discussion Need some JavaScript puzzles
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Jorge  
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 More options Sep 29 2008, 4:02 pm
Newsgroups: comp.lang.javascript
From: Jorge <jo...@jorgechamorro.com>
Date: Mon, 29 Sep 2008 13:02:58 -0700 (PDT)
Local: Mon, Sep 29 2008 4:02 pm
Subject: Re: Need some JavaScript puzzles
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On Sep 28, 9:04 pm, dhtml <dhtmlkitc...@gmail.com> wrote:

> Jorge wrote:
> > On Sep 24, 3:14 am, dhtml <dhtmlkitc...@gmail.com> wrote:
> >> 1. write a function return the binary representation of a given number
> >> in "ON" and "OFF".  For example, if the input is 47 (101111 in binary),
> >> it should return "ON OFF ON ON ON ON".

> >http://jorgechamorro.com/cljs/016/

> You could have used toString(radix).

> var n = 101111;

> n.toString(2).replace(/1/g, "ON ").
> replace(/0/g,"OFF ").replace(/ $/,'');

Now that you say it... yes. I completely forgot its existence :-)

Thanks for posting that because I have played with it a little and I
have learnt that it converts reals as well:

(3.1416).toString(2) ->
11.001001000011111111100101110010010001110100010100111

and that it will fail as miserably as mine and without warning (for
those numbers that a 'number' primitive value can't represent
accurately):

javascript:alert((9007199254740991).toString(2))  ->
11111111111111111111111111111111111111111111111111111
javascript:alert((9007199254740991.4).toString(2))->
11111111111111111111111111111111111111111111111111111
javascript:alert((9007199254740991.5).toString(2))->
100000000000000000000000000000000000000000000000000000
javascript:alert((9007199254740992).toString(2))  ->
100000000000000000000000000000000000000000000000000000
javascript:alert((9007199254740993).toString(2))  ->
100000000000000000000000000000000000000000000000000000

While writing 'my version', I was going to 'logically' test the bits
with an '&', but I have discovered that the & operator operates on
just 32 bits, not on the 53 available in the mantissa of a 'number'
primitive value:

javascript:alert(9007199254740991 & Math.pow(2,31)) ===
-10000000000000000000000000000000
javascript:alert(9007199254740991 & Math.pow(2,32)) === 0

--
Jorge.


 
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