calc crc32 for files

dummy_crc32.c

#include <windows.h>

typedef DWORD (__stdcall *_RtlComputeCrc32)(DWORD, const BYTE*, INT);

#define CRC32_BLOCK_SIZE 1024


DWORD get_crc32_of_file(LPCSTR sFileName)
{
    _RtlComputeCrc32 RtlComputeCrc32 = (_RtlComputeCrc32)GetProcAddress(LoadLibraryA("ntdll.dll"), "RtlComputeCrc32");

    HANDLE hFile = CreateFileA(sFileName, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

    if (hFile != INVALID_HANDLE_VALUE)
    {
        BYTE aBuf[CRC32_BLOCK_SIZE];
        DWORD dwCrc32 = 0, dwBytesRead;

        while (ReadFile(hFile, aBuf, CRC32_BLOCK_SIZE, &dwBytesRead, NULL) && dwBytesRead != 0) 
        {
            dwCrc32 = RtlComputeCrc32(dwCrc32, aBuf, dwBytesRead);
        }

        CloseHandle(hFile);

        return dwCrc32;
    }

    return -1;
}


void entry()
{
    char *aFiles[] = {"test_1.txt", "test_2.txt", "test_3.txt"};

    for (size_t i = 0; i < sizeof(aFiles) / sizeof(aFiles[0]); i++) {
        char aBuf[MAX_PATH + 20];
        wsprintfA(aBuf, "%s = %08X", aFiles[i], get_crc32_of_file(aFiles[i]));
        OutputDebugStringA(aBuf);
    }

    ExitProcess(0);
}