ファイルのMD5値を計算します

 

#include "stdafx.h"
#include <string>
#include <Windows.h>
#include <wincrypt.h>

using namespace std;

string ComputeFileMD5(const TCHAR *szFilename)
{
    HCRYPTPROV hCryptProv = 0;
    HCRYPTHASH hHash = 0;
    HANDLE hMapFile = 0;
    BYTE bHash[0x7f];
    DWORD dwHashLen = 16;
    BYTE *pBuf;
    string digest;
    DWORD dwFileSize = 0, dwHighFileSize = 0;
    HANDLE hFile = CreateFile(szFilename, GENERIC_READ, FILE_SHARE_READ, 0, OPEN_EXISTING, 0, 0);
    if (hFile == INVALID_HANDLE_VALUE)
    {
        return digest;
    }
    dwFileSize = GetFileSize(hFile, &dwHighFileSize);
    hMapFile = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
    if (hMapFile == NULL || hMapFile == INVALID_HANDLE_VALUE)
    {
        goto release;
    }
    if (CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET))
    {
        if (CryptCreateHash(hCryptProv, CALG_MD5, 0, 0, &hHash))
        {
            UINT64 filesize = (UINT64)dwHighFileSize << 32 | dwFileSize;
            for (UINT64 i = 0; i <= filesize; i += 1048576) // 1024*1024
            {
                size_t bufsize = size_t(min(filesize - i, 1048576));
                pBuf = (BYTE *)MapViewOfFile(hMapFile, FILE_MAP_READ, (DWORD)(i >> 32), (DWORD)i, bufsize);
                if (pBuf == NULL)
                {
                    goto release;
                }
                if (!CryptHashData(hHash, pBuf, bufsize, 0))
                {
                    goto release;
                }
                UnmapViewOfFile(pBuf);
            }
            if (CryptGetHashParam(hHash, HP_HASHVAL, bHash, &dwHashLen, 0))
            {
                digest.resize(32);
                BYTE value;
                for (int i = 0; i < 16; i++)
                {
                    value = bHash[i] >> 4;
                    digest[i * 2] = value < 10 ? char(value + '0') : char(value - 10 + 'a');
                    value = bHash[i] & 0x0F;
                    digest[i * 2 + 1] = value < 10 ? char(value + '0') : char(value - 10 + 'a');
                }
            }
        }
    }
release:
    CryptDestroyHash(hHash);
    CryptReleaseContext(hCryptProv, 0);
    UnmapViewOfFile(pBuf);
    CloseHandle(hMapFile);
    CloseHandle(hFile);
    return digest;
}