#include <stdio.h>
#include <stdlib.h>

void deblock(char *in, char *base64, FILE * OutputFile, int len)
{
 if (base64[(int)in[0]] < 64  && base64[(int)in[1]] < 64)
    fprintf(OutputFile, "%c",(base64[(int)in[0]] << 2 | base64[(int)in[1]] >> 4));
 if (base64[(int)in[1]] < 64  && base64[(int)in[2]] < 64)
    fprintf(OutputFile, "%c",(base64[(int)in[1]] << 4 | base64[(int)in[2]] >> 2));
 if (base64[(int)in[2]] < 64  && base64[(int)in[3]] < 64)

    fprintf(OutputFile, "%c",((base64[(int)in[2]] << 6) & 192) | base64[(int)in[3]]);
}

void decode (FILE *InputFile, FILE *OutputFile)
{
    static char base64[] = {
    // ASCII table
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 64, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
    64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
    64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};
    int len = 0;
    int i = 0;
    char buffer[4] = {0};
    while ((len = fread(buffer,sizeof(char),4,InputFile)) >= 1)
    {
        for (i = len; i < 4; i++)
            buffer[i] = 0;
            deblock(buffer,base64,OutputFile,len);
    }
}


int check_decode(FILE *file1, FILE *file2)
{
    int k = 0;
    fseek (file1, 0, SEEK_END);
    if (((ftell(file1)) % 4) == 0)
    {
        fseek(file1,0,SEEK_SET);
        decode(file1,file2);
    }
    else
    {
        k = -1;
    }
    return k;
}


int main()
{
    FILE *file1 = NULL;
    FILE *file2 = NULL;
    if (NULL == (file1 = fopen("INPUT1.txt", "r")))
    {
        printf("Can't open INPUT file!");
        return -1;
    }
    if (NULL == (file2 = fopen("OUTPUT.orig", "wb")))
    {
        printf("Can't create OUTPUT file");
        return -1;
    }
    if ( -1 == check_decode(file1, file2)       )
    {
        printf("Eto ne base64");
        return -1;
    }
    fclose(file1);
    fclose(file2);
    return 0;
}