What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

digital man

Snapple "Real Fact" #31:
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Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

digital man

Snapple "Real Fact" #31:
The average human will eat an average of 8 spiders while sleeping.
Norco, CA WX: 93.7øF, 38% humidity, 4 mph WSW wind, 0.00 inches rain/24hrs

The purpose of this algorithm is to make people such as myself feel inferior, even stupid for the fact that people such as myself do not have a logical bone in their body....:)
johnatuna
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Re: Challenge
By: Digital Man to All on Wed Jun 21 2006 01:16 pm

for(x=0; y!=0; x++)
y=y&(y-1);

Counts the number of bits set in y storing the result in x?

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Re: Challenge
By: Deuce to Digital Man on Wed Jun 21 2006 06:49 pm

Re: Challenge
By: Digital Man to All on Wed Jun 21 2006 01:16 pm

for(x=0; y!=0; x++)
y=y&(y-1);

Counts the number of bits set in y storing the result in x?

But of course. What else could it be? :-)

digital man

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Emus and Kangaroos cannot walk backwards.
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Re: Challenge
By: Digital Man to Deuce on Wed Jun 21 2006 06:11 pm

for(x=0; y!=0; x++)

y=y&(y-1);

Counts the number of bits set in y storing the result in x?

But of course. What else could it be? :-)

It *could* be:

x=0;
while(y=y&(y-1))
x++;


---
I find pleasure in knowing... this colours my words enough that people think I enjoy proving them wrong. Howver, I would be just as happy being proven wrong and knowing more than proving myself right. Please understand that any perceived rudeness is not intended. Rest assured that should I feel like being purposely rude, I will insult you personally and not attack your knowledge.

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In a reply from Johnatuna on 16:30 about Challenge

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

digital man

Snapple "Real Fact" #31:
The average human will eat an average of 8 spiders while sleeping.
Norco, CA WX: 93.7øF, 38% humidity, 4 mph WSW wind, 0.00 inches rain/24hrs

The purpose of this algorithm is to make people such as myself feel inferior,

ditto

even stupid for the fact that people such as myself do not have a logical bone
in their body....:)

hmmmm

Rob Starr
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Time Warp of the Future BBS
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Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

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Re: Re: Challenge
By: Tracker1 to Digital Man on Wed Jun 21 2006 11:22 pm

Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

digital man

Snapple "Real Fact" #3:
Beavers can hold their breathe for 45 minutes under water.
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Re: Re: Challenge
By: Digital Man to Tracker1 on Fri Jun 23 2006 01:00:00

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

The y=y&(y-1) expression is nicely obscure. And it neatly avoids
iterating over 0-bits as well.

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Re: Re: Challenge
By: Angus McLeod to Digital Man on Fri Jun 23 2006 08:21 am

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)

y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

The y=y&(y-1) expression is nicely obscure. And it neatly avoids
iterating over 0-bits as well.

Not as obscure or efficient (on average) as:
unsigned int const w = v - ((v >> 1) & 0x55555555);
unsigned int const x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
unsigned int const c = ((x + (x >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; return(c);



---
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Re: Re: Challenge
By: Deuce to Angus McLeod on Fri Jun 23 2006 11:04:00

The y=y&(y-1) expression is nicely obscure. And it neatly avoids iterating over 0-bits as well.

Not as obscure or efficient (on average) as:
unsigned int const w = v - ((v >> 1) & 0x55555555);
unsigned int const x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
unsigned int const c = ((x + (x >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; return(c);

I know that one better like this:

x -= (x >> 1) & 0x55555555;
x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
return ((x + (x >> 4) & 0x0f0f0f0f) * 0x01010101) >> 24;

which is essentially the same thing, but I prefer not to use additional variables if they can be avoided.

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Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

digital man

Snapple "Real Fact" #31:
The average human will eat an average of 8 spiders while sleeping.
Norco, CA WX: 93.7øF, 38% humidity, 4 mph WSW wind, 0.00 inches rain/24hrs

What kind of math is this? Calculus? I have always wanted to learn math but noone has sat down with me to teach me. Funny, a 35 year old man who does not know how to do math...what a damn shame...:)
johnatuna
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Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math but noone has sat down with me to teach me. Funny, a 35 year old man who does not know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

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Re: Re: Challenge
By: Ispyhumanfly to Johnatuna on Sun Jun 25 2006 06:53:00

for(starting value, limit, incriment) {
do something...
}

Loosely. This:

for (f=fopen("file.ext","r");!feof(f);fgets(buf,sizeof(buf),f) {
/* do something */
}

is still a functioning for() statement.
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Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math bu noone has sat down with me to teach me. Funny, a 35 year old man who does know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn.
One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?
johnatuna
Neophyte BBS Open 24/7 DoveNet/DarkNet Over 75 Gigs in Files! neophyte.synchro.net


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With interpidation and the MAGIC of QWK Mail Johnatuna wrote to

Ispyhumanfly <=-

Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math bu noone has sat down with me to teach me. Funny, a 35 year old man who does know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn. One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?

Y! (why not) ! means not /me !happy /me != happy

& is harder to grasp (at least for me) is a pointer.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

Someone else MAY say it better.





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Re: Re: Challenge
InternetMailingFinnigann

With interpidation and the MAGIC of QWK Mail Johnatuna wrote to

Ispyhumanfly <=-

Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math noone has sat down with me to teach me. Funny, a 35 year old man who do know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn. One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?

Y! (why not) ! means not /me !happy /me != happy

& is harder to grasp (at least for me) is a pointer.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

Someone else MAY say it better.

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Everything you just said, I understood...except for the pointer thing...hehehe...:)
Is this a particular language that I can read about to gain an understanding of the pointer thing?
johnatuna
Neophyte BBS Open 24/7 DoveNet/DarkNet Over 75 Gigs in Files! neophyte.synchro.net


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Re: Re: Challenge
By: Johnatuna to Ispyhumanfly on Sun Jun 25 2006 03:39:00

for(x=0; y!=0; x++)
y=y&(y-1);

I'm gong to get something out of this, so here it goes. X = 0..I understand I do not understand...what does the ! mean? Also explain what X++ and y& mea please. This looks interesting and I'd like to learn.
One would have to say this is a algebraic math atleast. Does not algebra dea with situational math?

The three parts of this for() statement are:

x=0;
Set x to zero before the loop begins.

y!=0;
Check y and confirm that it is != (not equal) to zero. If this
condition fails, the loop terminates.

x++;
A programming shorthand meaning "incriment x after it's been used."
This occurs after each execution of the loop body, before the
end condition is re-checked. (There is also ++x; which incriments
before use. In this case, before or after use makes no difference, but
post-incriment -- rather than pre-incriment -- is customary.)

The body of the loop contains

y=y&(y-1);
Assign to y "y=", the result of it's original value "y" bitwise-ANDed
"&" with itself minus one "(y-1)".



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Re: Re: Challenge
By: Finnigann to Johnatuna on Sun Jun 25 2006 08:37:00

for(x=0; y!=0; x++)
y=y&(y-1);

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn. One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?

& is harder to grasp (at least for me) is a pointer.

Not in this case.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

A clear enough description/explanation of pointers. But in this case, the
"&" is a bitwise-AND operator.

"y" is bitwise-ANDed with "itself-less-1" amd the result set back into "y".

Say y contained the value 156 (binary = 10011100). Then (y-1) would be
155 (binary = 10011011) and to perform the bitwuse AND we would do:

y = 156 = 10011100
(y-1) = 155 = 10011011
y = y&(y-1) = 152 = 10011000
^ ^^ <-- a bit is set in the result only where
a bit is present in both the first AND second operand to the bitwise-AND operator.

This statement (y=y&(y-1) eliminates the Least Significant Bit of y rather cleverly, leaving all the other bits unchanged.
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Re: Re: Challenge
By: Johnatuna to Finnigann on Sun Jun 25 2006 09:29:00

for(x=0; y!=0; x++)
y=y&(y-1);

Y! (why not) ! means not /me !happy /me != happy

& is harder to grasp (at least for me) is a pointer.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

Everything you just said, I understood...except for the pointer thing...hehehe...:)

Is this a particular language that I can read about to gain an understanding the pointer thing?

The example for() loop is in C/C++. Similar code works in other
languages, too. So the loop becomes:

for ($x=0; $y!=0; $x++) {
$y=$y&($y-1);
}

in Perl. (Perl uses a buck '$' to indicate a scalar variable, whereas
C/C++ does not. '$x' in Perl means 'x' in C/C++. Also, Perl *requires*
that you enclose the body of the loop in braces {}. C/C++ encloses the
body of a loop in braces too, but only if the body consists of more than a single statement*. Since y=y&(y-1); is a single statement, the C/C++
version does not require the {}.)

*Ok, not technically correct, but for all practical purposes...

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Re: Re: Challenge
By: Johnatuna to Ispyhumanfly on Sun Jun 25 2006 03:39 am

Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math noone has sat down with me to teach me. Funny, a 35 year old man who do know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand I do not understand...what does the ! mean? Also explain what X++ and y& mea please. This looks interesting and I'd like to learn.
One would have to say this is a algebraic math atleast. Does not algebra dea with situational math?
johnatuna
Neophyte BBS Open 24/7 DoveNet/DarkNet Over 75 Gigs in Files! neophyte.synchro.net

When you see an expression like y!=0, what you should read is y does not equal zero. The ! is used to say 'not'.
x++ is shorthand for x = x + 1, which increments x, for example (0, 1, 2, 3 ...). The ampersand? Got me right now. I'd have to go look it up. :P

Stormer

---
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Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math

but

noone has sat down with me to teach me. Funny, a 35 year old man who does

not

know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Math?) ;)

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Re: Re: Challenge
By: Screwball to Ispyhumanfly on Mon Jun 26 2006 05:48:00

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Math?) ;)

Technically, it would be simple arithmetic.

Not higher mathematics.



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Re: Challenge
By: Johnatuna to Digital Man on Sat Jun 24 2006 06:16 am

Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this?

It's C programming... you know.. Progamming... the name of this message area? :-)

Calculus? I have always wanted to learn math but
noone has sat down with me to teach me. Funny, a 35 year old man who does no know how to do math...what a damn shame...:)

I never learned calculus either. <shrug>

digital man

Snapple "Real Fact" #25:
The only food that does not spoil is honey.
Norco, CA WX: 102.0øF, 30% humidity, 2 mph WNW wind, 0.00 inches rain/24hrs

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Re: Re: Challenge
By: Finnigann to Johnatuna on Sun Jun 25 2006 08:37 am

With interpidation and the MAGIC of QWK Mail Johnatuna wrote to

Ispyhumanfly <=-

Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math noone has sat down with me to teach me. Funny, a 35 year old man who do know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn. One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?

Y! (why not) ! means not /me !happy /me != happy

& is harder to grasp (at least for me) is a pointer.

In this context, & is a bit-wise "AND". It has nothing to do with pointers or addresses.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

If "&x" were used in the expression, that would be true, but it's not.

digital man

Snapple "Real Fact" #70:
A "jiffy" is actually 1/100 of a second.
Norco, CA WX: 102.0øF, 30% humidity, 2 mph WNW wind, 0.00 inches rain/24hrs

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Re: Re: Challenge
By: Screwball to Ispyhumanfly on Mon Jun 26 2006 05:48 am

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math

but

noone has sat down with me to teach me. Funny, a 35 year old man who do

not

know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Math?) ;)

Actually, if a for loop you can also decrement (decrease something). A shuttle launch or microwave timer is a perfect example of this. (5..4..3..2..1..ding!). You'd express a decrement shorthand as x-- , for example.

Stormer

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With interpidation and the MAGIC of QWK Mail Digital Man wrote to Finnigann

<=-

Re: Re: Challenge
By: Finnigann to Johnatuna on Sun Jun 25 2006 08:37 am

With interpidation and the MAGIC of QWK Mail Johnatuna wrote to

Ispyhumanfly <=-

Re: Re: Challenge
InternetMailingIspyhumanfly

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn math noone has sat down with me to teach me. Funny, a 35 year old man who do know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...
}

--
ispyhumanfly +o euphoriabbs.net :: send comments to /dev/null...

I'm gong to get something out of this, so here it goes. X = 0..I understand Y! I do not understand...what does the ! mean? Also explain what X++ and y& means please. This looks interesting and I'd like to learn. One would have to say this is a algebraic math atleast. Does not algebra deal with situational math?

Y! (why not) ! means not /me !happy /me != happy

& is harder to grasp (at least for me) is a pointer.

In this context, & is a bit-wise "AND". It has nothing to do with
pointers or addresses.

X is a varible (it can be anything). That value is stored in a place in
memory. &X is the address of that place.

If "&x" were used in the expression, that would be true, but it's not.

My cover is blown. I only took a semester of C++ programming. Got a 'B'

http://www.kellogg.edu/infotech/cet/procertcore.html

It's a goal...




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Re: Challenge
InternetMailingDigital Man

Re: Challenge
By: Johnatuna to Digital Man on Sat Jun 24 2006 06:16 am

Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this?

It's C programming... you know.. Progamming... the name of this message area :-)

Calculus? I have always wanted to learn math but
noone has sat down with me to teach me. Funny, a 35 year old man who does know how to do math...what a damn shame...:)

I never learned calculus either. <shrug>

digital man

Snapple "Real Fact" #25:
The only food that does not spoil is honey.
Norco, CA WX: 102.0øF, 30% humidity, 2 mph WNW wind, 0.00 inches rain/24hrs

I know this is a programming area...duh...:)
But that did look like math. I once learned programming but have not done it
in years....I sucked because I did not know math.
I pretty much suck at everything in life, so please bare with my ignorance, I don't mean to cause problems.

johnatuna
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Re: Re: Challenge
By: Screwball to Ispyhumanfly on Mon Jun 26 2006 05:48 am

Johnatuna wrote:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this? Calculus? I have always wanted to learn

math

but

noone has sat down with me to teach me. Funny, a 35 year old man who

do

not

know how to do math...what a damn shame...:)

this isn't math, this is a for loop...

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Math?)

;)

Actually, if a for loop you can also decrement (decrease something). A shuttle
launch or microwave timer is a perfect example of this. (5..4..3..2..1..ding!). You'd express a decrement shorthand as x-- , for example.

Stormer

---

Well, maybe not a perfect example. ;)

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Re: Re: Challenge
By: Screwball to Ispyhumanfly on Mon Jun 26 2006 05:48:00

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Math?)

;)

Technically, it would be simple arithmetic.

Not higher mathematics.

I stand corrected, but do we have to get technical? ;)

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Re: Challenge
By: Johnatuna to Digital Man on Mon Jun 26 2006 05:32 pm

Re: Challenge
InternetMailingDigital Man

Re: Challenge
By: Johnatuna to Digital Man on Sat Jun 24 2006 06:16 am

Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this?

It's C programming... you know.. Progamming... the name of this message a :-)

Calculus? I have always wanted to learn math but
noone has sat down with me to teach me. Funny, a 35 year old man who d know how to do math...what a damn shame...:)

I never learned calculus either. <shrug>

I know this is a programming area...duh...:)
But that did look like math. I once learned programming but have not done it in years....I sucked because I did not know math.
I pretty much suck at everything in life, so please bare with my ignorance, don't mean to cause problems.

No problem. I was just giving you a good-natured "hard time". Don't sweat it. :-)

digital man

Snapple "Real Fact" #142:
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Re: Re: Challenge
By: Stormer to Screwball on Mon Jun 26 2006 13:28:00

Actually, if a for loop you can also decrement (decrease something). A shut launch or microwave timer is a perfect example of this. (5..4..3..2..1..ding!). You'd express a decrement shorthand as x-- , for example.

You don't *have* to do an incriment or decriment. Of course, you *can* incriment or decriment a counter, and many times, that's what programmers
do because that's what they need. But you can do virtually ANYTHING.

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Re: Re: Challenge
By: Screwball to Angus McLeod on Mon Jun 26 2006 21:29:00

for(starting value, limit, incriment) {
do something...

Okay, how do you increment a variable without Adding? (is this not Mat

Technically, it would be simple arithmetic.

Not higher mathematics.

I stand corrected, but do we have to get technical? ;)

I wasn't trying to be argumentative, but that little code-fragment that DM posted recently has prompted various reactions. Looking at various
fragments of the, uh, fragment, some people have oversimplifed and some
people have overcomplicated.


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Re: Challenge
InternetMailingDigital Man

Re: Challenge
By: Johnatuna to Digital Man on Mon Jun 26 2006 05:32 pm

Re: Challenge
InternetMailingDigital Man

Re: Challenge
By: Johnatuna to Digital Man on Sat Jun 24 2006 06:16 am

Re: Challenge
InternetMailingDigital Man

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

What kind of math is this?

It's C programming... you know.. Progamming... the name of this messag :-)

Calculus? I have always wanted to learn math but
noone has sat down with me to teach me. Funny, a 35 year old man wh know how to do math...what a damn shame...:)

I never learned calculus either. <shrug>

I know this is a programming area...duh...:)
But that did look like math. I once learned programming but have not done in years....I sucked because I did not know math.
I pretty much suck at everything in life, so please bare with my ignoranc don't mean to cause problems.

No problem. I was just giving you a good-natured "hard time". Don't sweat it :-)

digital man

Snapple "Real Fact" #142:
Hawaii is the only U.S. state never to report a temperature of zero degrees Norco, CA WX: 76.8øF, 50% humidity, 0 mph W wind, 0.00 inches rain/24hrs

Sorry about that post...yesterday was a day from hell for me. I had to
present a paper that was not ready. I'm in a classroom full of graduate students a hell of a lot smarter than I am and every class I leave feeling
like the stupidist son-of-a-bitch that ever lived. Until this point in my college career, I have been given help to get through my classes. Being learning disabled, and legally blind makes college a pain in the ass when you have no help. So yesterday's posting should not have been posted...sorry
about that. I just hope I didn't post any messages anyway making anyone
angry.

johnatuna
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Re: Re: Challenge
By: Stormer to Johnatuna on Sun Jun 25 2006 10:59 am

for(x=0; y!=0; x++)
y=y&(y-1);

When you see an expression like y!=0, what you should read is y does not equal zero. The ! is used to say 'not'.
x++ is shorthand for x = x + 1, which increments x, for example (0, 1, 2, 3 ...). The ampersand? Got me right now. I'd have to go look it up. :P

For even more fun the first line could bE:
for(x=0;y;x++)


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Re: Re: Challenge
By: Deuce to Stormer on Tue Jun 27 2006 12:01:00

for(x=0; y!=0; x++)
y=y&(y-1);

When you see an expression like y!=0, what you should read is y does not equal zero. The ! is used to say 'not'.
x++ is shorthand for x = x + 1, which increments x, for example (0, 1, 2, ...). The ampersand? Got me right now. I'd have to go look it up. :P

For even more fun the first line could bE:
for(x=0;y;x++)

and the second line could be

y&=y-1;

You could even code the entire thing as

for (x=1;y&=y-1;x++)
;

if you knew that there was at least ONE bit set...

;-)
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Re: Re: Challenge
By: Angus McLeod to Deuce on Tue Jun 27 2006 03:26 pm

Re: Re: Challenge
By: Deuce to Stormer on Tue Jun 27 2006 12:01:00

for(x=0; y!=0; x++)

y=y&(y-1);
for (x=1;y&=y-1;x++)
;

if you knew that there was at least ONE bit set...

You mean:
x=y?(({for(x=1;y&=y-1;x++);}),x):0;


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Re: Re: Challenge
By: Deuce to Angus McLeod on Tue Jun 27 2006 14:33:00

for(x=0; y!=0; x++)

y=y&(y-1);

for (x=1;y&=y-1;x++)
;

if you knew that there was at least ONE bit set...

You mean:
x=y?(({for(x=1;y&=y-1;x++);}),x):0;

Well, yes, but your new solution is actually longer than the original proposal, before even we began to reduce it with s few simplifications.
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Re: Re: Challenge
By: Angus McLeod to Deuce on Wed Jun 28 2006 12:02 am

for(x=0; y!=0; x++)

y=y&(y-1);

for (x=1;y&=y-1;x++)

;

if you knew that there was at least ONE bit set...

You mean:
x=y?(({for(x=1;y&=y-1;x++);}),x):0;

Well, yes, but your new solution is actually longer than the original proposal, before even we began to reduce it with s few simplifications.

Well, any test for y!=0 will result in more code any way I slice it... even: for(x=y?1:0;y&=y-1;x++);
and
if(y)for(x=1;y&=y-1;x++);

But how can you turn away from an excuse to use braces and the comma operator in the same statement?

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Re: Re: Challenge
By: Deuce to Angus McLeod on Wed Jun 28 2006 10:24:00

You mean:
x=y?(({for(x=1;y&=y-1;x++);}),x):0;

Well, yes, but your new solution is actually longer than the original proposal, before even we began to reduce it with s few simplifications.

Well, any test for y!=0 will result in more code any way I slice it... even: for(x=y?1:0;y&=y-1;x++);

I *like* this one!

and
if(y)for(x=1;y&=y-1;x++);

No, not so keen on this one! :-)

But how can you turn away from an excuse to use braces and the comma operato in the same statement?

Because I don't like the comma operator. Sure I use it when called for,
but I'd prefer a solution that doesn't use it.

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Re: Re: Challenge
By: Angus McLeod to Deuce on Wed Jun 28 2006 07:38 pm

But how can you turn away from an excuse to use braces and the comma operato in the same statement?

Because I don't like the comma operator. Sure I use it when called for,
but I'd prefer a solution that doesn't use it.

Well, if we're talking in real life, it would be more likely to be formulated as:

for(bits=0; val; bits++)
val&=val-1; /* Clear least significant bit */


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I find pleasure in knowing... this colours my words enough that people think I enjoy proving them wrong. Howver, I would be just as happy being proven wrong and knowing more than proving myself right. Please understand that any perceived rudeness is not intended. Rest assured that should I feel like being purposely rude, I will insult you personally and not attack your knowledge.

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Re: Re: Challenge
By: Deuce to Angus McLeod on Thu Jun 29 2006 12:26 am

Re: Re: Challenge
By: Angus McLeod to Deuce on Wed Jun 28 2006 07:38 pm

But how can you turn away from an excuse to use braces and the comma operato in the same statement?

Because I don't like the comma operator. Sure I use it when called for, but I'd prefer a solution that doesn't use it.

Well, if we're talking in real life, it would be more likely to be formulate as:

for(bits=0; val; bits++)
val&=val-1; /* Clear least significant bit */

Or even the brute-force, least efficient, but most readable:

for(i=0, bits=0; i<sizeof(val)*8; i++)
if(val&(1<<i))
bits++;

That's how *I* answered the interview question some 5+ years ago. <shrug>

digital man

Snapple "Real Fact" #85:
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Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

hmmm... what if you wanted to preserve y?

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Deuce wrote:

Not as obscure or efficient (on average) as:
unsigned int const w = v - ((v >> 1) & 0x55555555);
unsigned int const x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
unsigned int const c = ((x + (x >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; return(c);

/me thinks Deuce is *VERY* secure in his job.

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Re: Re: Challenge
By: Tracker1 to Digital Man on Mon Jul 03 2006 01:43:00

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

hmmm... what if you wanted to preserve y?

Maybe

for(t=y, x=0; t; x++)
t&=t-1;

would work? (But there's that comma again...)

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Re: Re: Challenge
By: Tracker1 to Digital Man on Mon Jul 03 2006 01:43 am

Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

hmmm... what if you wanted to preserve y?

v=y; // preserve value in 'y'
for(x=0; v!=0; x++)
v=v&(v-1);

digital man

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Re: Re: Challenge
InternetMailingTracker1

Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

hmmm... what if you wanted to preserve y?

--
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With help, I came to understand this algoryth. Can anyone explain &. This represents pointer? Pointer to what?
Before anyone like DM jumps my ass, please remember....I am wanting to learn!

johnatuna

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With help, I came to understand this algoryth. Can anyone explain &. This represents pointer? Pointer to what?
Before anyone like DM jumps my ass, please remember....I am wanting to learn

Dude, no one on this network jumps your ass for wanting to learn..
Maybe for wanted the information "handed" to you, with you doing no
work of your own.. But don't worry, no "ass jumping" happens here,
unless someone deserves it. =o)

Death



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Re: Re: Challenge
By: Johnatuna to Tracker1 on Mon Jul 03 2006 12:02 pm

Re: Re: Challenge
InternetMailingTracker1

Digital Man wrote:

What is the purpose of the following algorithm:

for(x=0; y!=0; x++)
y=y&(y-1);

sounds like someone that doesn't know how to use a sleep call.. :/

Nope. Deuce got it right. I should've exempted him! :-)

hmmm... what if you wanted to preserve y?

With help, I came to understand this algoryth. Can anyone explain &. This represents pointer? Pointer to what?
Before anyone like DM jumps my ass, please remember....I am wanting to learn

In this context, '&' represents a bit-wise "AND" operation (nothing to do with pointers).

If you take a binary number, like say, 0101101, and you "AND" it with another number, say, 1001001, the result is a value containing the bits "set" (to 1) in both numbers. i.e.

0101101
& 1001001
-------
= 0001001

The other bit-wise operations are "OR" (represented in C with the '|' symbol), "XOR" ('^' in C), and "NOT" ('~' in C). An "OR" operation results in a value with bits "set" in *either* number, i.e.

0101101
| 1001001
-------
= 1101101

An "XOR" operation results in a value with "set" bits only in positions where the 2 source numbers contain a different bit value (0 where they're the same). i.e.

0101101
^ 1001001
-------
= 1100100

A "NOT" operation takes a single operand (value to operate on) and results in a value with the inverse-bits set:

~ 0101101
-------
= 1010010

These are the bit-wise operators common to most programming language, although the syntax and use may differ a bit, the logic and results are the same.

digital man

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Re: Re: Challenge
By: Tracker1 to Digital Man on Mon Jul 03 2006 01:43 am

hmmm... what if you wanted to preserve y?

Store it first.

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Re: Re: Challenge
By: Tracker1 to Deuce on Mon Jul 03 2006 01:45 am

Not as obscure or efficient (on average) as:
unsigned int const w = v - ((v >> 1) & 0x55555555);
unsigned int const x = (w & 0x33333333) + ((w >> 2) & 0x33333333); unsigned int const c = ((x + (x >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; return(c);

/me thinks Deuce is *VERY* secure in his job.

Goodness, I didn't write that. It's in the Giant Lib of Usefull Functions.

---
I find pleasure in knowing... this colours my words enough that people think I enjoy proving them wrong. Howver, I would be just as happy being proven wrong and knowing more than proving myself right. Please understand that any perceived rudeness is not intended. Rest assured that should I feel like being purposely rude, I will insult you personally and not attack your knowledge.

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Re: Re: Challenge
By: Johnatuna to Finnigann on Sun Jun 25 2006 10:29 am

The exercise was a bit over my head, but in this case I think the '&' was used as a bitwise operator(as opposed to logical). I won't try to explain bitwise operators since, well, I can't LOL.

I kind of know what they are but haven't toyed with them enough to understand them that well. I'm sure there are others who will have a better explanation.

The '&' is also used with a variable name when it is used as a reference variable which is similar to a pointer. It's been a while since I touched that one too<grin>.

Everything you just said, I understood...except for the pointer thing...hehehe...:)
Is this a particular language that I can read about to gain an understanding the pointer thing?

C++ is the first one I would look at in this case. Specifically the parts on operators and loops. /////////////////////////////////////////////////////////////////////////////// /////// Chris Perrault ////////// ////// THE DIAMOND MINE BBS ////////// ///// Telnet bbs.dmine.net ////////// ///////////////////////////////////////////////////////////////////////////

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Re: Re: Challenge
By: Death to Johnatuna on Mon Jul 03 2006 04:41 pm

Is there a new extreme sport I'm not aware of? :-)
/s

But don't worry, no "ass jumping" happens here,
unless someone deserves it. =o)

Death

/////////////////////////////////////////////////////////////////////////////// /////// Chris Perrault ////////// ////// THE DIAMOND MINE BBS ////////// ///// Telnet bbs.dmine.net ////////// ///////////////////////////////////////////////////////////////////////////

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Re: Re: Challenge
InternetMailingChristopher Perrault

Re: Re: Challenge
By: Death to Johnatuna on Mon Jul 03 2006 04:41 pm

Is there a new extreme sport I'm not aware of? :-)
/s

But don't worry, no "ass jumping" happens here,
unless someone deserves it. =o)

Death

//////////////////////////////////////////////////////////////////////////// /////// Chris Perrault //////// ////// THE DIAMOND MINE BBS ///////// ///// Telnet bbs.dmine.net ////////// ///////////////////////////////////////////////////////////////////////////

Backhoe digging while on LSD...:)

johnatuna

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Re: Re: Challenge
By: Johnatuna to Christopher Perrault on Mon Aug 07 2006 02:46 am

Oooohh,, that sounds painfull<grin>. I'm sure hitting a gasline will be a real trip. LOL
/s

Backhoe digging while on LSD...:)

johnatuna

Neophyte BBS
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