C / C++ / MFC Discussion Boards

Mike Dimmick19-Apr-04 5:49

19-Apr-04 5:49

Logarithms in different bases can be done using the formula

log_y x = log_z x / log_z y

So you can use the log or log10 function to produce an approximate log2 function:

double log2(double val)
{
   return log(val) / log(2.0);
}

Stability. What an interesting concept. -- Chris Maunder

Re: log2

Navin19-Apr-04 5:51

Navin

19-Apr-04 5:51

Argh, beat me to it! You must have posted that while I was in the process of replying. Big Grin | :-D

Sometimes I feel like I'm a USB printer in a parallel universe.

Re: log2

The Lady of Shallots19-Apr-04 6:01

The Lady of Shallots

19-Apr-04 6:01

Perfect! Thanks so much!

"It seems that we're getting to the bottom of the barrel of squirrels." - my boss

Re: log2

Navin19-Apr-04 5:50

Navin

19-Apr-04 5:50

Use the Magic Log Forumla:

Log_b x = Log_a x/Log_a b

A funcion that can get an arbitrary log:

double MyLog(double base, double x)
{
  return log10(x) / log10(base);
}

...
double a = MyLog(2, 16);      // should be 4

Sometimes I feel like I'm a USB printer in a parallel universe.

Re: log2

toxcct19-Apr-04 6:05

toxcct

19-Apr-04 6:05

just a curiosity and "personal culture" question...

what should we need a Base-2 log for ??

very thank you

TOXCCT >>> GEII power

Re: log2

jmkhael19-Apr-04 6:24

jmkhael

19-Apr-04 6:24

A whole world of it:

Check on google log neperien

In breif:
Solving mathematical equations
Mathematical modeling of the movement of protons
Spatial Interpolation,
Mechanical modeling
Probability and statistics ....

Papa

while (TRUE)
Papa.WillLove ( Bebe ) ;

Re: log2

toxcct19-Apr-04 6:43

toxcct

19-Apr-04 6:43

wow woww stop it man, did you read my post ???

i didn't ask for log neperien (which is a Base-e log), but the need for having a log2 one !!!!

TOXCCT >>> GEII power

Re: log2

jmkhael19-Apr-04 6:52

jmkhael

19-Apr-04 6:52

Sorry for missreading your post
log2 is used in music among others for as octave utility

and for floating point arithmetics:
"By knowing that the exponent and mantissa are both two's compliment values and also knowing that a floating point number is a very close approximation of the same number expressed in log2 form, a quick inversions and square roots can be implimented with simple functions. For example a quick inverse is calculated by negating the exponent and mantissa bits."

Papa

while (TRUE)
Papa.WillLove ( Bebe ) ;

Re: log2

toxcct19-Apr-04 8:19

toxcct

19-Apr-04 8:19

powerful ! (paweurfoul Big Grin | :-D

thnk u vry much

TOXCCT >>> GEII power

Re: log2

David Crow19-Apr-04 8:31

David Crow

19-Apr-04 8:31

toxctt wrote:
what should we need a Base-2 log for ??

Since computers use base-2 numbers, binary logarithms come in very handy. For example, what is the next highest power of two for the number 79?

int x = 1 + (int) log2(79); // assuming log2() returns a double

If a binary tree has N nodes, what is the minimum number of levels in the tree? log2(13) + 1 yields the answer of 4.

http://www.encyclopedia4u.com/b/binary-logarithm.html

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: log2

toxcct19-Apr-04 8:35

toxcct

19-Apr-04 8:35

oh, that's nice ! lol
but since it's very useful, how to find such expression ? did you find such by yourself, or with docs ?

TOXCCT >>> GEII power

Re: log2

David Crow19-Apr-04 8:46

David Crow

19-Apr-04 8:46

toxcct wrote:
oh, that's nice ! lol

Are you laughing facetiously?

toxcct wrote:
how to find such expression ?

What expression?

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: log2

toxcct19-Apr-04 8:52

toxcct

19-Apr-04 8:52

DavidCrow wrote:
Are you laughing facetiously?

no, i promise you i find all these very nice...

DavidCrow wrote:
What expression?

such expression : int x = 1 + (int) log2(79);

TOXCCT >>> GEII power

Re: log2

David Crow19-Apr-04 8:59

David Crow

19-Apr-04 8:59

toxcct wrote:
such expression : int x = 1 + (int) log2(79);

I just made that statement up. A log2() function does not exist in the standard library, so if you needed one, it would have to be created.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: log2

toxcct19-Apr-04 9:03

toxcct

19-Apr-04 9:03

DavidCrow wrote:
log2() function does not exist in the standard library

yes, that was implicit and understood.
what i want to know is about the entiere expression (int x = 1 + (int) log2(79);) ; did you find it after been documented, or by a thinking of your own ?

TOXCCT >>> GEII power

Re: log2

David Crow19-Apr-04 9:17

David Crow

19-Apr-04 9:17

toxcct wrote:
did you find it after been documented, or by a thinking of your own ?

The latter. Since log₂(79) is 6.3, I needed to take the integer part of that and add one, yielding 7. Thus 2⁷ is 128, the next highest power of 2 for the number 79.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: log2

Antti Keskinen19-Apr-04 9:31

Antti Keskinen

19-Apr-04 9:31

This expression is a solution to the problem DavidCrow presented: "-- What is the next highest power of two for the number 79?"

The expression first evaluates the power to which 2 must be raised to reach 79, then adds 1 to this. It all bases on the way logarithms are defined: "Base N logarithm from number Y will result in the power to which N must be raised to result in Y".

Most obviously, he just made up a quick problem, and solved it, to give an example. So, he thought it on his own, made it up.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Re: log2

Robert A. T. Káldy19-Apr-04 22:19

Robert A. T. Káldy

19-Apr-04 22:19

Aaaarrrrgggghhh!! you really want to compute binary logarithm of integers with float logarithm function? I think that integer approach would be much much more quicker:

int log2(int x)
{
    int lg;
//  if (x <= 0) throw something...
    for(lg = -1; x != 0; x /= 2, lg++);
    return lg;
}

Robert-Antonio

"Science is a differerntial equation.
Religion is a boundary condition."

Re: log2

David Crow20-Apr-04 2:27

David Crow

20-Apr-04 2:27

Robert A. T. Káldy wrote:
...with float logarithm function

The log2() function I demonstrated was theoretical. Were it to be implemented, ints would surely be used over doubles.

Robert A. T. Káldy wrote:
I think...

But without actual metrics, we don't really know.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Killing a process

Shay Harel19-Apr-04 5:38

Shay Harel

19-Apr-04 5:38

Hi,

Is there a way to Kill a process programatically, something like :
KillProcess (name) ?

I want to kill a process which I can see in the process list of CTRL+ALT+DEL and I want to make sure it's not there before doing something.

Thanks,
Shay

Re: Killing a process

jmkhael19-Apr-04 6:14

jmkhael

19-Apr-04 6:14

One lame way to do so:
http://www.sysinternals.com/ntw2k/freeware/pstools.shtml
you can issue a call to pskill or do your own using

or open the process and issue a call to TerminateProcess

or using
http://www.codeproject.com/threads/pausep.asp
and replacing the SuspendThread by TerminateThread

Papa

while (TRUE)
Papa.WillLove ( Bebe ) ;

Killing a process

Anonymous19-Apr-04 5:38

Anonymous

19-Apr-04 5:38

Printer problem

jancsi19-Apr-04 5:25

jancsi

19-Apr-04 5:25

Hi anybody has any idea about this : how to print a html file (in html format , not text format) without showing any printer dialog and being able to customize the orientation (portrait/landscape) . Any links are welcome

Thanks

xxx

Error in W98

doctorpi19-Apr-04 5:25

doctorpi

19-Apr-04 5:25

Hi guys
When my App is running in W98 I receive sometimes a "Resource necessary non available".
There is a way to avoid this message in W98? Programatically? With an utility?
Best Regards
Doc

Re: Error in W98

David Crow19-Apr-04 9:01

David Crow

19-Apr-04 9:01

At the point in which the message is displayed, what resource is your application asking for (e.g., bitmap, icon, menu, dialog, string table)?

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.