CRC32 Fun - How do I initialize a const static int array in an un-managed C++ class (VS2003/C++)

[Russell Mangel]

Hi,

I would like to encapsulate the following CRC32 routine inside a C++
un-mananged class.
I am having difficulty initializing the "const static unsigned int table[]"
inside an un-managed C++ class.

I would like the lookup table to remain static so it is loaded only once on
program startup.
I do not want to create the lookup table using a loop, if possible

Can you help me create a class for this CRC32 routine? I am using VS2003/C++

Thanks,
Russell Mangel Las Vegas, NV

#include "stdafx.h"

// The CRC lookup table
const static unsigned int table[] =
{
0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419,
0x0706AF48F, 0x0E963A535, 0x09E6495A3,
0x00EDB8832, 0x079DCB8A4, 0x0E0D5E91E, 0x097D2D988, 0x009B64C2B,
0x07EB17CBD, 0x0E7B82D07, 0x090BF1D91,
0x01DB71064, 0x06AB020F2, 0x0F3B97148, 0x084BE41DE, 0x01ADAD47D,
0x06DDDE4EB, 0x0F4D4B551, 0x083D385C7,
0x0136C9856, 0x0646BA8C0, 0x0FD62F97A, 0x08A65C9EC, 0x014015C4F,
0x063066CD9, 0x0FA0F3D63, 0x08D080DF5,
0x03B6E20C8, 0x04C69105E, 0x0D56041E4, 0x0A2677172, 0x03C03E4D1,
0x04B04D447, 0x0D20D85FD, 0x0A50AB56B,
0x035B5A8FA, 0x042B2986C, 0x0DBBBC9D6, 0x0ACBCF940, 0x032D86CE3,
0x045DF5C75, 0x0DCD60DCF, 0x0ABD13D59,
0x026D930AC, 0x051DE003A, 0x0C8D75180, 0x0BFD06116, 0x021B4F4B5,
0x056B3C423, 0x0CFBA9599, 0x0B8BDA50F,
0x02802B89E, 0x05F058808, 0x0C60CD9B2, 0x0B10BE924, 0x02F6F7C87,
0x058684C11, 0x0C1611DAB, 0x0B6662D3D,
0x076DC4190, 0x001DB7106, 0x098D220BC, 0x0EFD5102A, 0x071B18589,
0x006B6B51F, 0x09FBFE4A5, 0x0E8B8D433,
0x07807C9A2, 0x00F00F934, 0x09609A88E, 0x0E10E9818, 0x07F6A0DBB,
0x0086D3D2D, 0x091646C97, 0x0E6635C01,
0x06B6B51F4, 0x01C6C6162, 0x0856530D8, 0x0F262004E, 0x06C0695ED,
0x01B01A57B, 0x08208F4C1, 0x0F50FC457,
0x065B0D9C6, 0x012B7E950, 0x08BBEB8EA, 0x0FCB9887C, 0x062DD1DDF,
0x015DA2D49, 0x08CD37CF3, 0x0FBD44C65,
0x04DB26158, 0x03AB551CE, 0x0A3BC0074, 0x0D4BB30E2, 0x04ADFA541,
0x03DD895D7, 0x0A4D1C46D, 0x0D3D6F4FB,
0x04369E96A, 0x0346ED9FC, 0x0AD678846, 0x0DA60B8D0, 0x044042D73,
0x033031DE5, 0x0AA0A4C5F, 0x0DD0D7CC9,
0x05005713C, 0x0270241AA, 0x0BE0B1010, 0x0C90C2086, 0x05768B525,
0x0206F85B3, 0x0B966D409, 0x0CE61E49F,
0x05EDEF90E, 0x029D9C998, 0x0B0D09822, 0x0C7D7A8B4, 0x059B33D17,
0x02EB40D81, 0x0B7BD5C3B, 0x0C0BA6CAD,
0x0EDB88320, 0x09ABFB3B6, 0x003B6E20C, 0x074B1D29A, 0x0EAD54739,
0x09DD277AF, 0x004DB2615, 0x073DC1683,
0x0E3630B12, 0x094643B84, 0x00D6D6A3E, 0x07A6A5AA8, 0x0E40ECF0B,
0x09309FF9D, 0x00A00AE27, 0x07D079EB1,
0x0F00F9344, 0x08708A3D2, 0x01E01F268, 0x06906C2FE, 0x0F762575D,
0x0806567CB, 0x0196C3671, 0x06E6B06E7,
0x0FED41B76, 0x089D32BE0, 0x010DA7A5A, 0x067DD4ACC, 0x0F9B9DF6F,
0x08EBEEFF9, 0x017B7BE43, 0x060B08ED5,
0x0D6D6A3E8, 0x0A1D1937E, 0x038D8C2C4, 0x04FDFF252, 0x0D1BB67F1,
0x0A6BC5767, 0x03FB506DD, 0x048B2364B,
0x0D80D2BDA, 0x0AF0A1B4C, 0x036034AF6, 0x041047A60, 0x0DF60EFC3,
0x0A867DF55, 0x0316E8EEF, 0x04669BE79,
0x0CB61B38C, 0x0BC66831A, 0x0256FD2A0, 0x05268E236, 0x0CC0C7795,
0x0BB0B4703, 0x0220216B9, 0x05505262F,
0x0C5BA3BBE, 0x0B2BD0B28, 0x02BB45A92, 0x05CB36A04, 0x0C2D7FFA7,
0x0B5D0CF31, 0x02CD99E8B, 0x05BDEAE1D,
0x09B64C2B0, 0x0EC63F226, 0x0756AA39C, 0x0026D930A, 0x09C0906A9,
0x0EB0E363F, 0x072076785, 0x005005713,
0x095BF4A82, 0x0E2B87A14, 0x07BB12BAE, 0x00CB61B38, 0x092D28E9B,
0x0E5D5BE0D, 0x07CDCEFB7, 0x00BDBDF21,
0x086D3D2D4, 0x0F1D4E242, 0x068DDB3F8, 0x01FDA836E, 0x081BE16CD,
0x0F6B9265B, 0x06FB077E1, 0x018B74777,
0x088085AE6, 0x0FF0F6A70, 0x066063BCA, 0x011010B5C, 0x08F659EFF,
0x0F862AE69, 0x0616BFFD3, 0x0166CCF45,
0x0A00AE278, 0x0D70DD2EE, 0x04E048354, 0x03903B3C2, 0x0A7672661,
0x0D06016F7, 0x04969474D, 0x03E6E77DB,
0x0AED16A4A, 0x0D9D65ADC, 0x040DF0B66, 0x037D83BF0, 0x0A9BCAE53,
0x0DEBB9EC5, 0x047B2CF7F, 0x030B5FFE9,
0x0BDBDF21C, 0x0CABAC28A, 0x053B39330, 0x024B4A3A6, 0x0BAD03605,
0x0CDD70693, 0x054DE5729, 0x023D967BF,
0x0B3667A2E, 0x0C4614AB8, 0x05D681B02, 0x02A6F2B94, 0x0B40BBE37,
0x0C30C8EA1, 0x05A05DF1B, 0x02D02EF8D
};
unsigned int GetCRC32(const unsigned char* bytes, const unsigned int len)
{
unsigned int crc = 0xFFFFFFFF;
unsigned char byte;

for(unsigned int i = 0; i < len; i++)
{
byte = crc ^ bytes[i];
crc = (crc >> 8) ^ table[byte];
}
return crc ^ 0xFFFFFFFF;
}

int _tmain(int argc, _TCHAR* argv[])
{
unsigned char bytes[] = { 0xAA, 0xBB, 0xCC };
const unsigned int crc = GetCRC32(bytes, 3);

// crc = 3192780876
std::cout << crc << std::endl;
return 0;
}

[Ben Schwehn]

I don't know if this is the recommended way of doing that (it seems
ugly), but it works:
[cut down the array to 5 entries]
#include "stdafx.h"

const int SIZE = 5;
class Test {
public:
// The CRC lookup table
const static unsigned int table[SIZE];

unsigned int GetCRC32(const unsigned char* bytes, const unsigned int len)
{
unsigned int crc = 0xFFFFFFFF;
unsigned char byte;

for(unsigned int i = 0; i < len; i++)
{
crc = (crc >> 8) ^ table[byte];
}
return crc ^ 0xFFFFFFFF;
}
};
const unsigned int Test::table[SIZE] =
{
0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419

};
int _tmain(int argc, _TCHAR* argv[])
{
unsigned char bytes[] = { 0xAA, 0xBB, 0xCC };
Test tst;
tst.GetCRC32(by tes, 3);

return 0;
}

[Russell Mangel]

Ben, thanks for your sample code, you have helped me.

I am converting some C# classes to un-managed CPP (CRC32 is one of them).
Sounds funny to make the previous statement, but it is neccessay, I am
coding against "MAPI" in C++ using (IJW).

I am very good with C# class design, but not so good with C++ class design.
Designing this simple C++ CRC32 class brings a question to me:

The GetCRC32 is heavily used, and so I was trying to get the lookup table
array in static memory, so the lookup table is not loaded for every call to
GetCRC32.
I am assuming that we have the table loaded in static memory by using the
keyword "static" in C++.
But exactly where in memory is the table, if it is in stack memory, then
"Automatic storage", and "Static Storage" must be on the stack.

I understand there are three types of memory in C++.
Automatic storage, Static storage, Free storage.

Have we successfully accomplished my goal?

Thanks
Russell Mangel
Las Vegas, NV

[Ben Schwehn]

Russell,

The GetCRC32 is heavily used, and so I was trying to get the lookup table
array in static memory, so the lookup table is not loaded for every call to
GetCRC32.
The lookup table is loaded once at program startup.

I am assuming that we have the table loaded in static memory by using the
keyword "static" in C++.
But exactly where in memory is the table, if it is in stack memory, then
"Automatic storage", and "Static Storage" must be on the stack.

It's in the static storage, not the stack.

you have a certain degree of control over in which data segment it is
loaded with the data_seg pragma. But I'm no expert in this area.

hth

--
Ben
http://bschwehn.de