How does this swap() work?

[xuyao]

Hi ALL,
I don't know why the function bellow can change the pointer of the two value
*x *y?
void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

[santosh]

xuyao wrote:

Hi ALL,
I don't know why the function bellow can change the pointer of the two value
*x *y?
void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

Break open your C textbook and look-up what the bitwise exclusive OR
operator does. Writing out the operations on paper will help you to
understand.

[xuyao]

On 7 13 , 4 43 , santosh <[e-mail]:

xuyao wrote:

Hi ALL,
I don't know why the function bellow can change the pointer of the two value
*x *y?

void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

Break open your C textbook and look-up what the bitwise exclusive OR
operator does. Writing out the operations on paper will help you to
understand.

I konw now ,i wonder why they use that kind of swap(),is that swap()
above faster than this function bellow or the other reasons

void fun(int *x, int *y)
{
int temp;
temp = *x;
*x = *y;
*y = temp;
}

[Chris McDonald]

xuyao <xu******@gmail.comwrites:

>I konw now ,i wonder why they use that kind of swap(),is that swap()
above faster than this function bellow or the other reasons

>void fun(int *x, int *y)
{
int temp;
temp = *x;
*x = *y;
*y = temp;
}

I don't believe that anyone with an eye for understandable, clear,
portable code uses that XOR technique.

It's often provided as a (poor) learning exercise for undergraduate students
and, once understood, should be dispatched to the trashcan of geeky tricks.

--
Chris.

[Chris Dollin]

Chris McDonald wrote:

xuyao <xu******@gmail.comwrites:

>>I konw now ,i wonder why they use that kind of swap(),is that swap()
above faster than this function bellow or the other reasons

>>void fun(int *x, int *y)
{
int temp;
temp = *x;
*x = *y;
*y = temp;
}

I don't believe that anyone with an eye for understandable, clear,
portable code uses that XOR technique.

It's often provided as a (poor) learning exercise for undergraduate students
and, once understood, should be dispatched to the trashcan of geeky tricks.

Especially since it [the XOR-* hack] is broken in the degenerate case.

--
RIP Donald Michie 11 November 1923 - 7 July 2007

Hewlett-Packard Limited Cain Road, Bracknell, registered no:
registered office: Berks RG12 1HN 690597 England

[Richard Bos]

xuyao <xu******@gmail.comwrote:

On 7 13 , 4 43 , santosh <[e-mail]:

xuyao wrote:

I don't know why the function bellow can change the pointer of the two value
*x *y?

void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

Break open your C textbook and look-up what the bitwise exclusive OR
operator does. Writing out the operations on paper will help you to
understand.

I konw now ,i wonder why they use that kind of swap(),is that swap()
above faster than this function bellow or the other reasons

void fun(int *x, int *y)
{
int temp;
temp = *x;
*x = *y;
*y = temp;
}

Quite the contrary. Since the version with the temporary variable is
more logical, more expressive, and corresponds better to what really is
supposed to happen, it is more likely to be optimised well than the XOR
hack. Therefore, this code is better in all counts, and the first code
should be relegated to the scrap-books of schoolboy hacks.

Richard

[Army1987]

On Fri, 13 Jul 2007 16:09:35 +0800, xuyao wrote:

Hi ALL,
I don't know why the function bellow can change the pointer of the two value
*x *y?

....as long as x doesn't equal y...

>
void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

--
Army1987 (Replace "NOSPAM" with "email")
"Never attribute to malice that which can be adequately explained
by stupidity." -- R. J. Hanlon (?)

[osmium]

"xuyao" writes:

On 7 13 , 4 43 , santosh <[e-mail]:

>xuyao wrote:

Hi ALL,
I don't know why the function bellow can change the pointer of the two
value
*x *y?

void swap(int *x,int *y)
{
*x = *x ^ *y;
*y = *x ^ *y;
*x = *x ^ *y;
}

Break open your C textbook and look-up what the bitwise exclusive OR
operator does. Writing out the operations on paper will help you to
understand.

I konw now ,i wonder why they use that kind of swap(),is that swap()
above faster than this function bellow or the other reasons

Because they want to show the world how incredibly bright they are. Their
mommy didn't praise them enough when she potty-trained them.