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'Int' is faster than 'Char'

P: n/a
Hi,

How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .

Can someone here provide some info regarding this.

Thanks and Regards,
Karthik Balaguru

Aug 13 '07 #1
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12 Replies


P: n/a
karthikbalaguru wrote:
Hi,

How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .
In which context?

--
Ian Collins.
Aug 13 '07 #2

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On Aug 13, 8:57 am, Ian Collins <ian-n...@hotmail.comwrote:
karthikbalaguru wrote:
Hi,
How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .

In which context?

--
Ian Collins.
Is 'Int' really faster than 'Char' ?

Thx in advans,
Karthik Balaguru

Aug 13 '07 #3

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karthikbalaguru wrote:
On Aug 13, 8:57 am, Ian Collins <ian-n...@hotmail.comwrote:
>karthikbalaguru wrote:
>>Hi,
How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .
In which context?
*Please don't quote signatures*
>
Is 'Int' really faster than 'Char' ?
In which context? It is significant.

--
Ian Collins.
Aug 13 '07 #4

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karthikbalaguru <ka***************@gmail.comwrites:
How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .

Can someone here provide some info regarding this.
C is a case-sensitive language. 'Int' and 'int' are two different
identifiers (actually an identifier and a keyword), as are 'Char' and
'char'. So your question is:

How is 'int' faster than 'char'.

int and char are types. Types do not have speed in any meaningful
sense. Specific operations on types might be faster or slower than
specific operations on other types.

So your real question is something like:

How are operations on operands of type 'int' faster than the same
operations on operands of type 'char'.

As far as the C language is concerned, the question is *still*
meaningless. The language doesn't say anything about that the
relative speeds of different operations, and such things can and often
do vary from one implementation to another.

On *some* systems, operations on 'int' can indeed be faster than
operations on 'char', because the hardware is designed to operate
efficiently on 'word'-sized chunks of data. For example, suppose int
is 32 bits, and char is 8 bits (other sizes are possible). The CPU
might have instructions to load, store, and operate on 32-bit chunks
of data. It might not have such instructions for 8-bit data; instead,
to load an 8-bit value, it might have to load a 32-bit value and
extract the desired 8 bits. To store an 8-bit value, it might have to
load 32 bits, use bitwise operations to set the desired 8-bit subset,
and then store 32 bits.

On other systems, operations on 8-bit values might be faster than
operations on 32-bit values. Or they might be exactly the same speed.

The standard (C99 6.2.5p5) says:

A "plain" int object has the natural size suggested by the
architecture of the execution environment ...

This suggests, but does not require, that an int is typically one
"word", and that operations on it are likely to be efficient.

If you want to have a single object, or a few individual objects,
intended to hold only small values, it's likely (but by no means
guaranteed) that using 'int' will give you the fastest code. Using
'char' instead might increase the size of your code more than it
reduces the size of your objects.

On the other hand, if you want large arrays of such objects, the space
saved by using 'char' could be more important.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Aug 13 '07 #5

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On Sun, 12 Aug 2007 20:53:54 -0700, karthikbalaguru wrote:
Hi,

How is 'Int' Faster than 'Char' ?
I think , 'Char' is small and so it should be easily & efficiently .

Can someone here provide some info regarding this.

Thanks and Regards,
Karthik Balaguru
If you have C99, use int_fast8_t in <stdint.h(or _Bool if it is
what you need) if this bothers you.
--
Army1987 (Replace "NOSPAM" with "email")
No-one ever won a game by resigning. -- S. Tartakower

Aug 13 '07 #6

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karthikbalaguru <ka***************@gmail.comwrote:
# Hi,
#
# How is 'Int' Faster than 'Char' ?
# I think , 'Char' is small and so it should be easily & efficiently .

Depends on the hardware. Memory might be optimised for word
access, with bytes requiring extra hardware or software fiddling.
CPU operations might only accept int sized values, with extra
steps of widenning and thinning chars. Or the hardware could be
optimised for char over int. It really depends on the machine
and the intended customer.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
The whole world's against us.
Aug 13 '07 #7

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karthikbalaguru wrote:
I have provided Info found in that doc.
Since 'int' is the fastest data type in C, "Method 1" is better than
any other implementations.

Method 1)
typedef int BOOLEAN
#define TRUE(1)
#define FALSE(0)

Method 2)
typedef char BOOLEAN
#define TRUE(1)
#define FALSE(0)
Whatever the relative speeds might have been, both of these
methods are syntactically incorrect -- for two different
reasons.
So, It has been stated 'int' is faster than 'char' .
Of the above two type of methods, Method 2 is found to be slow because
it uses 'char'.
Is it so ? How ?
It depends on how they are used. (Sometimes, when `char` is rather
smaller than `int`, that allows code to run faster, or even run
rather than not, because big boolean arrays won't be as big.)

In any case, such speed variation is a property of /a particular
implementation/, used in /a particular way/, so you can't appeal
to the standard for an answer, and if you want to appeal to
other programmers, you'd better be specific about how you're
using the Methods and what platform you're using and what you're
performance goals are.

--
Semicolons And Spaces For Sale Hedgehog
"Our future looks secure, but it's all out of our hands"
- Magenta, /Man and Machine/

Aug 13 '07 #8

P: n/a
karthikbalaguru <ka***************@gmail.comwrites:
[...]
Method 1)
typedef int BOOLEAN
#define TRUE(1)
#define FALSE(0)

Method 2)
typedef char BOOLEAN
#define TRUE(1)
#define FALSE(0)
These definitions are syntax errors. You need a ';' on the typedefs,
and a space after 'TRUE' and 'FALSE', and the parentheses are
unnecessary.

Personally, my favorite way to define a boolean type in C (if _Bool
and <stdbool.h aren't available) is:

typedef enum { false, true } bool;

If you choose to define 'TRUE' and 'FALSE', it's important to remember
*not* to compare a value for equality with TRUE. For example:

BOOLEAN b = some_condition;
if (b == TRUE) /* ... */ WRONG!

Any non-zero value is considered true; the comparison will fail if b
has any value other than 0 or 1. Instead, since b is already a boolean,
just test it directly:

if (b) /* ... */ OK

This is *much* more important than any concerns about performance.

See section 9 of the comp.lang.c FAQ, <http://www.c-faq.com/>.
So, It has been stated 'int' is faster than 'char' .
Of the above two type of methods, Method 2 is found to be slow because
it uses 'char'.
In addition to fact that the relative performance is system-specific,
it's entirely possible that some operations will be faster for char
than for int, and other operations will be faster for int than for
char.

It's not very likely that the difference either way is going to be
significant. Write clear and correct code. If it works, and it's
fast enough, you're done. If it works, but it's not fast enough, you
can start looking for ways to speed it up. It's easier to make good
code fast than to make fast code good.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Aug 13 '07 #9

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On Tue, 14 Aug 2007 09:49:09 +0200, Ravishankar S wrote:

[about using int or char]
In this context it will not matter much since its boolean (usually used as
return type). So not much runtime wasted. But it saves memory (if used for
static or global vars). In one case int is definitely faster than char : On
most RISC processors use of int rather than char for a loop index.
If you don't care about time and want to save space, use char.
--
Army1987 (Replace "NOSPAM" with "email")
No-one ever won a game by resigning. -- S. Tartakower

Aug 14 '07 #10

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Army1987 wrote:
If you don't care about time and want to save space, use char.
An array of char will save space over an array of int,
but for single or a few objects,
it is possible that all byte size objects may be aligned on an int
boundary and so, not really saving any usable space.

On my machine, the output of new.c is:

The address of ca is 0012FF7C
The address of cb is 0012FF78
The address of cc is 0012FF74

/* BEGIN new.c */

#include <stdio.h>

int main(void)
{
char ca = 0;
char cb = 0;
char cc = 0;

printf("The address of ca is %p\n", (void *)&ca);
printf("The address of cb is %p\n", (void *)&cb);
printf("The address of cc is %p\n", (void *)&cc);
return 0;
}

/* END new.c */

--
pete
Aug 14 '07 #11

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On Aug 14, 3:25 pm, pete <pfil...@mindspring.comwrote:
Army1987 wrote:
If you don't care about time and want to save space, use char.

An array of char will save space over an array of int,
but for single or a few objects,
it is possible that all byte size objects may be aligned on an int
boundary and so, not really saving any usable space.

On my machine, the output of new.c is:

The address of ca is 0012FF7C
The address of cb is 0012FF78
The address of cc is 0012FF74

/* BEGIN new.c */

#include <stdio.h>

int main(void)
{
char ca = 0;
char cb = 0;
char cc = 0;

printf("The address of ca is %p\n", (void *)&ca);
printf("The address of cb is %p\n", (void *)&cb);
printf("The address of cc is %p\n", (void *)&cc);
return 0;

}

/* END new.c */

--
pete
Sounds interesting . So, it is not necessarily only that of
Structure's that behave like that .
So, Even, single object behave like that. That sounds
interesting :-):-).

Karthik Balaguru

Aug 14 '07 #12

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Army1987 wrote:
>
On Tue, 14 Aug 2007 05:31:27 -0700, karthikbalaguru wrote:
On Aug 14, 3:25 pm, pete <pfil...@mindspring.comwrote:
Army1987 wrote:
If you don't care about time and want to save space, use char.

An array of char will save space over an array of int,
but for single or a few objects,
it is possible that all byte size objects may be aligned on an int
boundary and so, not really saving any usable space.
ca only occupies 0012FF7C. A char occupies one byte. An array
of three chars occupies three bytes. Simply, the placement of
automatic variable is unspecified.
But my point is, that the space saved that way,
may or may not be *usable* space.

It's only extremely very rarely that I declare a single object
of a type which is subject to integer promotions.

--
pete
Aug 17 '07 #13

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