binary conversion

[bimbam]

Hi,

I wish to compare 2 black and white images of about 4000 pixels. So I have 2 arrays of 4000 integers int of value 0 or 1. My idea was to convert each array to a single binary number built by putting all the integers one after the other. I could then convert this number to a base 10 number. I would use this number as a signature of each image to compare them.

The problem is the amount of operations to make to build the binary number. Multiplying each 4000 number by a power of 10 and summing everything is longer than comparing directly each frame pixel by pixel. (As I have a lot of images, I think it's worth doing it anyway).

So would you have a method you think would be faster to build the binary number? In fact, it might be possible to use only the last bit of the pixel value integer and store it directly in 4000 bit zone. But I don't know how to do that.

Regards

[weaknessforcats]

Are you using C++??

If so, use a bitset rather than integers:
[code=cpp]
bitset<4000> array1;
bitset<4000> array2;

if(array1 == array2)
{
cout << "Bits are equal" <<endl;
}
[/code]

This way you use 8000 bits instead of 8000 integers.

[bimbam]

Are you using C++??

If so, use a bitset rather than integers:
[code=cpp]
bitset<4000> array1;
bitset<4000> array2;

if(array1 == array2)
{
cout << "Bits are equal" <<endl;
}
[/code]

This way you use 8000 bits instead of 8000 integers.

Thank you for the tip.

I don't use C++ but there might be a function in C to do the same?

Regards

[weaknessforcats]

You write the function in C++ and compile it as extern "C":

[code=cpp]
extern "C" int CompareBits(bit set<4000>& array1, bitset<4000>arr ay2)
{

if (array1 == array2) return 1; //true
return false;
}
[/code]

Usually you can have a mixture of C and C++ files in the same IDE project. Visual Studio compiles are .c files using rules of C and all .cpp files using rules of C++.

The extern "C" is a command to the compiler to not alter the name of the function. That way the name remains as CompareBits. Otherwise, the compiler will has the name and the arguments into a unique string. It's how C++ handles multiple functions with the same name.

[weaknessforcats]

Oops. No bitsets in C for the function arguments.

Let me post again in a minute.

[weaknessforcats]

OK. Let;s try this again.

Here is possible C code:
[code=c]
#include <stdio.h>


#define FALSE 0
#define TRUE !FALSE

void* CreateBitArray( );
int CompareBitArray (void* array1, void* array2);

int main()
{
void* array1 = CreateBitArray( );
void* array2 = CreateBitArray( );

if(CompareBitAr ray(array1, array2) == TRUE)
{
printf("Bits are equal\n");
}
}
[/code]

Here the 4000 bit bitsets are created by a C++ function that returns a pointer to the bits.

Then the bitsets are compared by a C++ function that returns a TRUE/FALSE.

This would be in a .c file.

The C++ code might be:
[code=cpp]
#include <bitset>
using namespace std;

extern "C"
void* CreateBitArray( )
{
bitset<4000>* b = new bitset<4000>;
return reinterpret_cas t<void*> (b);
}

extern "C" int CompareBitArray (void* array1, void* array2)
{
bitset<4000>* a1 = reinterpret_cas t<bitset<4000>* > (array1);
bitset<4000>* a2 = reinterpret_cas t<bitset<4000>* > (array2);
if (a1 == a2) return 1; //true
return 0; //false
}
[/code]

The C++ code is an a .cpp file.

Essentially, you would write wrappers in C++ that could be called fromn C. These wrappers would allow you to use any bitset methods you wanted.

[bimbam]

OK. Let;s try this again.

Here is possible C code:
[code=c]
#include <stdio.h>


#define FALSE 0
#define TRUE !FALSE

void* CreateBitArray( );
int CompareBitArray (void* array1, void* array2);

int main()
{
void* array1 = CreateBitArray( );
void* array2 = CreateBitArray( );

if(CompareBitAr ray(array1, array2) == TRUE)
{
printf("Bits are equal\n");
}
}
[/code]

Here the 4000 bit bitsets are created by a C++ function that returns a pointer to the bits.

Then the bitsets are compared by a C++ function that returns a TRUE/FALSE.

This would be in a .c file.

The C++ code might be:
[code=cpp]
#include <bitset>
using namespace std;

extern "C"
void* CreateBitArray( )
{
bitset<4000>* b = new bitset<4000>;
return reinterpret_cas t<void*> (b);
}

extern "C" int CompareBitArray (void* array1, void* array2)
{
bitset<4000>* a1 = reinterpret_cas t<bitset<4000>* > (array1);
bitset<4000>* a2 = reinterpret_cas t<bitset<4000>* > (array2);
if (a1 == a2) return 1; //true
return 0; //false
}
[/code]

The C++ code is an a .cpp file.

Essentially, you would write wrappers in C++ that could be called fromn C. These wrappers would allow you to use any bitset methods you wanted.

Thanks,

I'll try that.

Regards

[bimbam]

How do you link the 2 files together?

Regards

[weaknessforcats]

If you are using an IDE like Visual Studio, you add both files to the same project and build. Visual Studio compiles all files with .c extensions as C code and all files with .cpp extensions as C++ code. Therefore, any project can be a mixture of C and C++ code.

If you are writing your own makefile, then use a C compiler on the .c file and a C++ compiler on the .cpp file. Route both object files to the linker.

[bimbam]

If you are using an IDE like Visual Studio, you add both files to the same project and build. Visual Studio compiles all files with .c extensions as C code and all files with .cpp extensions as C++ code. Therefore, any project can be a mixture of C and C++ code.

If you are writing your own makefile, then use a C compiler on the .c file and a C++ compiler on the .cpp file. Route both object files to the linker.

Hi,

I tried to compile the examples you sent me. I try to use a Makefile but I'm not too familiar with it. Could you give me a help? Do I need a header file?

I called the 2 files you sent me main.c and test.cpp. Here is my makefile:

CC=gcc
CPP=g++
CFLAGS=-W -Wall -ansi -pedantic
CXXFLAGS=-W -Wall -ansi -pedantic
LDFLAGS=
EXEC=test

all: $(EXEC)

test: test.o main.c
        $(CC) -o $@ $^ $(CFLAGS) $(LDFLAGS)

test.o: test.cpp
        $(CPP) -o $@ $< $(CXXFLAGS)

The errors are:

gcc -o test test.o main.c -W -Wall -ansi -pedantic
main.c: In function ‘main’:
main.c:18: warning: control reaches end of non-void function
test.o: In function `CreateBitArray ':
test.cpp:(.text +0x3f): undefined reference to `operator new(unsigned int)'
test.o:(.eh_fra me+0x11): undefined reference to `__gxx_personal ity_v0'
collect2: ld returned 1 exit status
make: *** [test] Error 1


Regards

[weaknessforcats]

I can't do makefiles much myself since I rely on the IDE - and it's Windows to boot so the make files are in different formats and are read differently.

Perhaps a gcc/g++ person here can help you. JosAH usually has answers for stuff like this.

[bimbam]

OK.

So JosAH (or anyone) can you help me?

Regards.

[JosAH]

Hi,

I tried to compile the examples you sent me. I try to use a Makefile but I'm not too familiar with it. Could you give me a help? Do I need a header file?

I called the 2 files you sent me main.c and test.cpp. Here is my makefile:

CC=gcc
CPP=g++
CFLAGS=-W -Wall -ansi -pedantic
CXXFLAGS=-W -Wall -ansi -pedantic
LDFLAGS=
EXEC=test

all: $(EXEC)

test: test.o main.c
        $(CC) -o $@ $^ $(CFLAGS) $(LDFLAGS)

test.o: test.cpp
        $(CPP) -o $@ $< $(CXXFLAGS)

The errors are:

gcc -o test test.o main.c -W -Wall -ansi -pedantic
main.c: In function ‘main’:
main.c:18: warning: control reaches end of non-void function
test.o: In function `CreateBitArray ':
test.cpp:(.text +0x3f): undefined reference to `operator new(unsigned int)'
test.o:(.eh_fra me+0x11): undefined reference to `__gxx_personal ity_v0'
collect2: ld returned 1 exit status
make: *** [test] Error 1


Regards

Well, you've got one warning: main() doesn't return anything and C doesn't like
that but even worse you have a link (collect) error because you're linking a
piece of C++ code as if it were plain C. The undefined reference to __gxx_etc.
thing is just an artifact because of that.

My suggestion is to go the whole nine yards either for C++ or C, but not both
of them. A bitset is just an array of (unsigned) ints or chars as far as C is
concerned. A simple memcmp() can compare those. Or you use C++ where
you can express the same more elegantly.

kind regards,

Jos