Plain Base64

plain_b64.c

#include <stdio.h>

const char kBase64Alphabet[64] = {
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '-'
};

const char kBase64Padding = '=';

int main(int argc, char** argv)
{

    for (int i = 1; i < argc; i++)
    {
        char buffer = 0;
        int j = 0;
        for (int j = 0; ; ++j)
        {
            char ch = argv[i][j];
            int rem = j % 3;

            // 8  - 6; => 2
            // 10 - 6; => 4
            // 12 - 6; => 6
            // 6  - 6; => 0

            switch (rem)
            {
            case 0:
            {
                if (ch == 0)
                {
                    break;
                }

                char sx = ch >> 2;
                putchar(kBase64Alphabet[sx]);
                buffer = ch & 0x3;
            }
            break;
            case 1:
            {
                char sx = ((buffer << 4) & 0x30) | (ch >> 4);
                putchar(kBase64Alphabet[sx]);
                buffer = ch & 0xf;

                if (ch == 0)
                {
                    putchar(kBase64Padding);
                    putchar(kBase64Padding);
                    break;
                }
            }
            break;
            case 2:
            {
                char sx = (buffer << 2) | (ch >> 6);
                putchar(kBase64Alphabet[sx]);
                if (ch == 0)
                {
                    putchar(kBase64Padding);
                    break;
                }
                putchar(kBase64Alphabet[ch & 0x3f]);
            }
            break;
            }
        }
        putchar('\n');
    }
    return 0;
}