Bit-tweaking in Javascript

Question

Just curious. I did a program in C, with quite an amount of bitwise operations for a variable which defines access controls for a page. I wanna be able to do the same in Javascript only. How can i accomplish this ordeal?

Any help in bit-tweaking in Javascript will help. Remember no costly functions allowed.

May I recommend you don't write C in JavaScript. Try to use JavaScript like a functional dynamic language instead. — Raynos
– Raynos, Commented Mar 16, 2011 at 13:10
I guess i wasn't clear. C coding was used for the server side development. Javascript for the client side. I just wanted to avoid overloading the server. Hence my question. — Ashwin Krishnamurthy
– Ashwin Krishnamurthy, Commented Mar 16, 2011 at 13:33
I meant do write JavaScript code in a C-style. It can be easy to write procedural style code in javascript due to the syntax similarities but it just becomes a mess. There really shouldn't be much reason to use bit manipulation in JavaScript apart from classics such as hashing functions. — Raynos
– Raynos, Commented Mar 16, 2011 at 16:08
Ahh, Alright. I'll try my best to avoid it. Thanks for the insight! — Ashwin Krishnamurthy
– Ashwin Krishnamurthy, Commented Mar 16, 2011 at 16:36

T.J. Crowder · Accepted Answer · 2011-03-16 11:53:30Z

1

JavaScript has the usual assortment of bitwise operators, |, &, ~, etc.; details in the specification.

The following sections will be particularly useful:

Section 11.4.8: Bitwise NOT (~)
Section 11.7: Bitwise Shift Operators (<< and >>)
Section 11.10: Binary Bitwise Operators (| and &)

Note that JavaScript's numbers are all floating point (see Section 8.5, The Number Type, in the specification), but the bitwise operations are defined in terms of integers. So for instance, the definition of the bitwise NOT operator:

11.4.8 Bitwise NOT Operator ( ~ )
The production UnaryExpression : ~ UnaryExpression is evaluated as follows:
1. Let expr be the result of evaluating UnaryExpression.
2. Let oldValue be ToInt32(GetValue(expr)).
3. Return the result of applying bitwise complement to oldValue. The result is a signed 32-bit integer.

Any decent implementation will be able to handle these efficiently, avoiding unnecessary conversions from Number to internal integer and back.

answered Mar 16, 2011 at 11:53

T.J. Crowder

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2 Comments

Ashwin Krishnamurthy Over a year ago

Thank you. Quite comprehensive.

HBP Over a year ago

And for even more details see bateru.com/news/2011/03/…

Jay · Accepted Answer · 2011-03-16 11:54:31Z

1

JavaScript has bitwise operators like other languages. Bitwise operators are, by definition, efficient. You should be able to replicate all the bitwise operations performed in your C program in JS as well.

http://www.eecs.umich.edu/~bartlett/jsops.html

answered Mar 16, 2011 at 11:54

Jay

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