Using bitshift in assigning a number to a variable?

[bollod]

Is there any benefit to declaring a variable:

x = (1<<12);

instead of:

x = 4096;

(besides the geek appeal of course ;-) )

I have seen these kind of declarations come up in some code I have been
fiddling with and was wondering if there was any tangible benefit, (I have
also seen stuff declared as hex, is there any benefit to that either).

---
bollod

[pete]

Robert Bachmann wrote:

bollod wrote:

What would you do if you needed to create the mask '10101010' (besides
foo=170 or foo=0xA4)?

I would write
#define SOME_MASK (1<<7 | 1<<5 | 1<<3 | 1<<1)

Out of all of the various replies posted,
that form, shifts and bitwise ors,
is similar to macros that I've actually used.

--
pete

[Sean Kenwrick]

----- Original Message -----
From: "Richard Heathfield" <do******@addre ss.co.uk.invali d>
Newsgroups: comp.lang.c
Sent: 27 December 2003 11:12
Subject: Re: Using bitshift in assigning a number to a variable?

bollod wrote:

On Fri, 26 Dec 2003 04:03:30 +0000, pete wrote:

It's easier to visualise the binary representation
of the values that way,
which is especially good if your numbers are masks.

That makes sense.

What would you do if you needed to create the mask '10101010' (besides
foo=170 or foo=0xA4)?

#define l )*2+1
#define O )*2
#define b1 ((((((((0

unsigned char foo = b1 l O l O l O l O ;

Hey this is pretty neat way of representing binary in your 'C' code. I
would generalise it a bit further by allowing 16 and 32 bit values as well,
something like:

#define bin32bit ((((((((((((((( ((((((((((((((( ((0
#define bin16bit ((((((((((((((( (0
#define bin8bit ((((((((0

#define O )<<1
#define I )<<1+1
Then

x=bin8bit I O I O I O I O

or

x = bin16bit I O I O I O I O I O I O I O I O

nice!

Sean

[Richard Heathfield]

Sean Kenwrick wrote:

----- Original Message -----
From: "Richard Heathfield" <do******@addre ss.co.uk.invali d>
Newsgroups: comp.lang.c
Sent: 27 December 2003 11:12
Subject: Re: Using bitshift in assigning a number to a variable?

bollod wrote:

> On Fri, 26 Dec 2003 04:03:30 +0000, pete wrote:
>
>> It's easier to visualise the binary representation
>> of the values that way,
>> which is especially good if your numbers are masks.
>
> That makes sense.
>
> What would you do if you needed to create the mask '10101010' (besides
> foo=170 or foo=0xA4)?

#define l )*2+1
#define O )*2
#define b1 ((((((((0

unsigned char foo = b1 l O l O l O l O ;

Hey this is pretty neat way of representing binary in your 'C' code. I
would generalise it a bit further by allowing 16 and 32 bit values as
well,

Yes, that's why I called it b1 rather than b - to allow for b2 and b4 (and,
if you have bigger integral types, b8 and so on as well).

See "Expert C Programming (Deep C Secrets)" by Peter van der Linden, p203,
for the original idea. All I did was hack the names.

--
Richard Heathfield : bi****@eton.pow ernet.co.uk
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