specific python if construct

Question

I'm trying to translate a Python utility to Ruby. The problem is that don't understand python very well.

A fragment of the utility includes the following if conditional:

if bits&0x10==0x10:

What does that mean? bits is a variable. Is it some kind of "shortened" "&&", meaning if bits is nonzero and has the value 0x10? Thanks!

BTW, there is no && in python, and bits and 0x10==0x10 will do something quite different. — Wooble
– Wooble, Commented Feb 19, 2013 at 17:06

entropy · Accepted Answer · 2013-02-19 17:03:44Z

6

The & alone is the bitwise and operation. Ie, bits is compared with 0x10 bit by bit and if both have a bit of 1 for that position the result is 1 for that position, otherwise 0.

Basically, since 0x10 is 10000 in binary, this is checking if the 5th bit in bits is set to 1.

I don't know much ruby, but my guess is, it should have a bitwise and operator and it would probably be & as well. Therefore this particular piece of code would end up being exactly the same in ruby.

Edit: according to the Ruby Operators page. Under section "Ruby Bitwise Operators", & acts as a bitwise and in ruby as well, so you can keep this as is in your translation of utility and it should, indeed, work.

answered Feb 19, 2013 at 17:03

entropy

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Abhijit · Accepted Answer · 2013-02-19 17:09:36Z

5

It actually checks if the 5th bit of the variable bits is set

How it works

& is bitwise anding.
0x10 is hex of binary value 0b10000
So you do a bit wise anding of what ever is in bits with 0b10000

Moreover, Ruby supports the similar construct for bit wise testing

if (bits&0x10)
    ......
end

Note as Tim mentioned, your Python construct can be simplified as

if bits&0x10:
    .......

edited Feb 19, 2013 at 17:09

answered Feb 19, 2013 at 17:03

Abhijit

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sureshvv · Accepted Answer · 2013-02-19 17:05:14Z

0

& is the binary bitwise "and" operator.

0x10 is hexadecimal 10.

You may want to read the python docs here

http://docs.python.org/2/reference/expressions.html

answered Feb 19, 2013 at 17:05

sureshvv

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