# Implementing the division operator

Discussion in 'C Programming' started by Sri, May 1, 2006.

1. ### SriGuest

Hi,

Is there anyway I can implement division in C without using the '/'
operator? Can I use bit aritmetic or such?

Thanks,
Sri

Sri, May 1, 2006

2. ### Michael MairGuest

Sri schrieb:
> Is there anyway I can implement division in C without using the '/'
> operator?

Yes:

int divide (int dividend, int divisor)
{
int sign = 1;
int result = 0;
if (dividend == 0)
return 0;
else if (dividend > 0) {
sign *= -1;
dividend *= -1;
}
if (divisor == 0) {
/* handle error */
}
else if (divisor > 0) {
sign *= -1;
divisor *= -1;
}
while (dividend < 0) {
dividend -= divisor;
++result;
}
return result;
}

> Can I use bit aritmetic or such?

If you want to.

If this is a homework assignment or similar, please state so.

Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

Michael Mair, May 1, 2006

3. ### osmiumGuest

"Sri" writes:

> Is there anyway I can implement division in C without using the '/'
> operator? Can I use bit aritmetic or such?

Yes, you could use repeated subtraction, which is what division is really
about. You could be even more obscure and use bitwise operations if you
wished.

osmium, May 1, 2006
4. ### SriGuest

Thanks Michael. This is *not* a *homework* assignment. This was shot at
me by a friend and it was picking my brain.

Sri, May 1, 2006
5. ### SriGuest

Can't we be more efficient? If I were to divide 100,000 by 2, it will
make 50,000 iterations of the while loop!

- Sri

Sri, May 1, 2006
6. ### SriGuest

Can't we do better than repeated subtraction? Could we say
powf(10, (log(dividend) - log(divisor));

Sri, May 1, 2006
7. ### osmiumGuest

"Sri" writes:

> Can't we do better than repeated subtraction? Could we say
> powf(10, (log(dividend) - log(divisor));

Please use Usenet protocol and quote the message to which you referring.
The people at Google have invented their own perverse, poorly thought out,
method and tried to superimpose it on Usenet.

osmium, May 1, 2006

Sri wrote:
> Can't we be more efficient? If I were to divide 100,000 by 2, it will
> make 50,000 iterations of the while loop!

Sure, you can use the normal bit-per-cycle algorithm using shift,
compare, and subtract. You have to be careful to avoid overflows.

--

9. ### SriGuest

I was referring to this:

"Yes, you could use repeated subtraction, which is what division is
really
about. You could be even more obscure and use bitwise operations if
you
wished. "

> Please use Usenet protocol and quote the message to which you referring.
> The people at Google have invented their own perverse, poorly thought out,
> method and tried to superimpose it on Usenet.

Sri, May 1, 2006
10. ### void * clvrmnky()Guest

Sri wrote:
> I was referring to this:
>
> "Yes, you could use repeated subtraction, which is what division is
> really
> about. You could be even more obscure and use bitwise operations if
> you
> wished. "
>
>> Please use Usenet protocol and quote the message to which you referring.
>> The people at Google have invented their own perverse, poorly thought out,
>> method and tried to superimpose it on Usenet.

>

And do try not to top-post.

There really are few rules on USENET.

void * clvrmnky(), May 1, 2006
11. ### peteGuest

Sri wrote:
>
> Can't we be more efficient? If I were to divide 100,000 by 2, it will
> make 50,000 iterations of the while loop!

unsigned fs_div(unsigned x, unsigned y)
{
unsigned a, b, q, counter;

q = 0;
if (y != 0) {
while (x >= y) {
a = x >> 1;
b = y;
counter = 1;
while (a >= b) {
b <<= 1;
counter <<= 1;
}
x -= b;
q += counter;
}
}
return q;
}

--
pete

pete, May 1, 2006
12. ### Default UserGuest

Sri wrote:

> Can't we be more efficient? If I were to divide 100,000 by 2, it will
> make 50,000 iterations of the while loop!

See below.

Brian
--
Please quote enough of the previous message for context. To do so from
Google, click "show options" and use the Reply shown in the expanded

Default User, May 1, 2006
13. ### SriGuest

Will do so....Thanks!

Default User wrote:
> Sri wrote:
>
> > Can't we be more efficient? If I were to divide 100,000 by 2, it will
> > make 50,000 iterations of the while loop!

>
> See below.
>
>
>
> Brian
> --
> Please quote enough of the previous message for context. To do so from
> Google, click "show options" and use the Reply shown in the expanded

Sri, May 1, 2006
14. ### SriGuest

Thanks pete!

pete wrote:
> Sri wrote:
> >
> > Can't we be more efficient? If I were to divide 100,000 by 2, it will
> > make 50,000 iterations of the while loop!

>
> unsigned fs_div(unsigned x, unsigned y)
> {
> unsigned a, b, q, counter;
>
> q = 0;
> if (y != 0) {
> while (x >= y) {
> a = x >> 1;
> b = y;
> counter = 1;
> while (a >= b) {
> b <<= 1;
> counter <<= 1;
> }
> x -= b;
> q += counter;
> }
> }
> return q;
> }
>
> --
> pete

Sri, May 2, 2006