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I had to read what you had written several times. I gather that you have sets of data which is 2 bits in length (ie. of values 0 to 3)
The following code will get the value of the 2 bits at index i. I don't know what you mean by this being a 2D array. You would probably want to check that nArrayPos doesn't go over the bounds of the compressedArray.
<br />
unsigned char GetAt(unsigned char *compressedArray, int i)<br />
{<br />
int nArrayPos = i / 4;<br />
int nBytePos = (3 - (i % 4)) * 2;<br />
return (compressedArray[nArrayPos] >> nBytePos) & 0x03;<br />
}<br />
If you want to check which bit is set for the result you could always do something like
<br />
if((result & 0x02) == 0x02)
if((result & 0x01) == 0x01)
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Actually, my problem is to decode a collision map wich is "compressed" for an old school 2D game.
It's like I had explained above (values are stored as set of 2 bits) and the values are stored as short in the file, so the values are inverted because of little endian.
For example:
the following line in the map would look like this (here, the width is 20 columns):
1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1
In the file, it is coded this way:
0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 1 0 0 0
the "1" means there is a wall, "0" means no wall.
the values are inverted. so I need to reverse them to get the correct decoding.
It drives me crazy 
How to do that?
Fred.
There is no spoon.
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It looks like you may have either misrepresented your problem or I have misunderstood. You said that values are stored as a set of 2 bits (which can have 4 values from 0 to 3).. but it looks like it is just 1 bit (with a value of either 0 or 1)?
When doing bitwise operations though, always think of operating on the big-endian representation.
Since Windows is little endian... you can modify the function accordingly. While the values are held as little-endian, the bitwise operations are conceptually done in big-endian so you don't have to logically flip it yourself.
<br />
unsigned char GetAt(unsigned short *compressedArray, int i)<br />
{<br />
int nArrayPos = i / 16;<br />
int nBytePos = (15 - (i % 16));<br />
return (compressedArray[nArrayPos] >> nBytePos) & 0x01;<br />
}<br />
edit: 1 0 0 0 is a short? does that mean it is using 4 bits to represent 1 value of either 0 or 1? Actually that snippet seems to make no sense since ordering is per byte.. so I don't know how 1 0 0 0 gets represented into 0 0 0 1.
-- modified at 12:01 Saturday 25th March, 2006
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Hi,
I was wrong by talking about short sorry.
by 1 0 0 0 I was meaning 01 00 00 00 = 8 bits = 1 byte.
The values are stored as set of 2 bits (values are between 0 - 3), but the sets are inverted in the file.
The values meaning are the following:
00 : nothing
01 : wall
10 : ladder
11 : tree
So, for example, when in the file there is the byte value:
0x68 : 01 10 10 00
the real values should be interpreted as:
0x29 : 00 10 10 01
1 byte means 4 cells of the array.
The series of 2 bits are inverted.
See what I mean?
So, the compressed array's size is (MapWidth/2)x(MapHeight/2).
for example if you have a tiny 4x8 map like this: (t1)
1 1 1 1 1 1 1 1
1 0 2 2 0 0 0 1
1 0 2 2 0 0 0 1
1 1 1 1 1 1 1 1
In the collision map coded like this in memory: (t2)
01 01 01 01 01 01 01 01
01 00 10 10 00 00 00 01
01 00 10 10 00 00 00 01
01 01 01 01 01 01 01 01
and in the file it is like this: (t3)
01 01 01 01 01 01 01 01
10 10 00 01 01 00 00 00
10 10 00 01 01 00 00 00
01 01 01 01 01 01 01 01
in hexa as bytes it looks like this:
0x55 0x55
0xa1 0x40
0xa1 0x40
0x55 0x55
the size of the compressed array is 2x4 like I wrote above (MapWidth/2)x(MapHeight/2)
In the unsigned char* it is coded like this (in the file)
0x55 0x55 0xa1 0x40 0xa1 0x40 0x55 0x55
so, in our example, GetAt(compressedArray, 3, 1) should returns 2 (0x10 - column 3, line 1 from t2)
while it is read from the compressedArray...
I hope it is clearer with a concrete example.
I'm sure there is a way to decode it on the fly without storing the decompressed array.
Thanks for the help
Best regards.
Fred.
There is no spoon.
-- modified at 12:20 Saturday 25th March, 2006
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Just a tweak to the function should get it to work.
You can just do GetAt(compressedArray, x + y * MapWidth) to get the cell you are interested in.
<br />
unsigned char GetAt(unsigned char *compressedArray, int i)<br />
{<br />
int nArrayPos = i / 4;<br />
int nBytePos = (i % 4) * 2;<br />
return (compressedArray[nArrayPos] >> nBytePos) & 0x03;<br />
}<br />
Don't get what you mean by decode on the fly, isn't this decoding on the fly?
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it always return 1 
There is no spoon.
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ok got it!!!
It works!!!
many thanks 
Fred.
There is no spoon.
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Hello hfry,
Do you remember me and my problem about bits?
You gave me the function that reads the values and it works perfectly. Now, I need the reciproque function: I need to write values...
I remind you the function for reading the data you kindly gave me:
int GetCollisionValue(unsigned char* collisionsMap, int x, int y, int nWidth)
{
int i=x+y*nWidth;
int nArrayPos = i / 4;
int nBytePos = (i % 4) * 2;
int value=(collisionsMap[nArrayPos] >> nBytePos) & 0x03;
return value;
}
Now, I need the "SetAt" function...
void SetAt(unsigned char* collisionsMap, int x, int y, int nWidth, int nValue);
Can you help me again please???
Best regards.
Fred.
There is no spoon.
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how to code for finding some related info based on keywords like "id", "name" etc
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what's your question exactly ?
i doubt anybody can understand you.
please also indicate which data types you're handling...
sincerely, ![Rose | [Rose]](https://www.codeproject.com/script/Forums/Images/rose.gif)
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lets say i have a program, its a reservation system. i have a db connected to it, and when click a button "Find", it will find related info based on keywords provided like "ReserveNo", "Name", etc.
im not very good at telling wat i want, cause im very new with this... sry
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well, what you want seems to be some SQL queries...
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I would like to distribute a font file with my app. The font I have is a little too large for my liking, 3.6mb. Using winrar I am able to compress it down to 1.2mb which is a little more realistic.
Obviously There is a chance that winrar will not be installed on the target machine so I need some sort of runtime decrompression algorithm. The idea is, I compress the file and add it to the resources/installer then simply deflate it onto the target machine.
I know of zlib, but I have never used it. Could anybody recomend a good algorithm, with not much overhead, will not increae the exe size too much, and fairly easy to implement? This is not an MFC project
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This for the links, I will into them
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I am using Visual c++ 6.0.
Where can I found a class that make DateTimePicker Flat like i found for ComboBox
Urgent
I learn my self
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No Body can reply me at this forum !
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Hi,
I've an application which creates HTML files. For that i'm using some database operations, which includes classes such as, CDatabase and CRecordSet etc.
I'm getting an exception as "invalid cursor" since m_strCursor is getting set to some file name e.g. "test.html", which the application is creating. I'm not able to trace out, how the variable is getting set. Similarly, m_strFilter, m_strSort, m_strUpdateSQL, m_strRequeryFilter, m_strRequerySort are getting set to the same file name.
Thanks,
Kranti
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Cool, that is what I was looking for. Thanks.
Now one more thing - is there any preprocessor variable that indicates what compiler is compiling the code? I want to write this macro seperately once for VC8 and once for VC6/VC7 so that the code can still be compiled with the older compiler, just in case someone wants to use the older compilers.
thanks!
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Guys,
* How to find my system get connected to LAN alone
not internet.
* IsNetworkAlive() API results in compilation error. AS
It requires Sensapi.h and its not found in my sysem.
where could I get this file?.
You only have to do a very few things right in your life so long as you don't do too many things wrong.
Vivek.S
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vivek.s.vivek wrote: It requires Sensapi.h and its not found in my sysem. where could I get this file?.
Download latest PSDK from MSDN site or seach cds comes with MSDN subscriptions.
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