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  Copying a 2 Dim Array into a 1 dim array  (Read 1593 times)
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Offline Mojomonkey

Senior Duke




ooh ooh eee eeee


« Posted 2003-07-09 19:27:34 »

Is there any speedier ways to copy a uniform (i.e. square) two dimesional array into a single dimesional array?

Something faster than:
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float[][] source = new float[size][size];
float[] target = new float[size * size];

// .... source is filled

for(int i = size; i < size; i++) {
    for(int j = size; j < size; j++) {
        target[j*size + i] = source[i][j];
    }
}

Don't send a man to do a monkey's work.
Offline nickdotjava

Junior Duke




I have fallen to the dark side. &nbsp;I'm using DX9


« Reply #1 - Posted 2003-07-09 19:41:37 »

As far as I know, that's the way to do it.

And is that the actual code, or something quickly written for the post?  There are a few bugs (loops never entered)...

-Nick

"Oh ya, that's trivial.  I should have it done in an hour."
Offline Mojomonkey

Senior Duke




ooh ooh eee eeee


« Reply #2 - Posted 2003-07-09 19:45:29 »

just wrote something up real quick for the post.

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Offline mik

Senior Newbie




Java games rock everywhere!


« Reply #3 - Posted 2003-07-09 20:41:40 »

and a System.arraycopy instead of the second loop?
like :
for (int i = 0; i < size; i++)
{
  System.arraycopy(source, 0, target, i*size, size);
}

as the source and the target have same type

Duh

Mik
Offline tortoise

Junior Duke




<3 Shmups


« Reply #4 - Posted 2003-07-12 00:49:15 »

Sun would claim arraycopy is faster. I don't remember the details on that method but it uses some native trickery to boost its speed.
Offline princec

JGO Kernel


Medals: 403
Projects: 3
Exp: 16 years


Eh? Who? What? ... Me?


« Reply #5 - Posted 2003-07-12 05:07:19 »

Arraycopy only has to do one bounds check.
The server VM should eliminate the bounds checks and also remove the native call overhead but it's probably neck and neck. But because almost no-one has the server VM (grrr!) you'll be better off with the arraycopy method I suspect.

Cas Smiley

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