dr. Derek Denkins-Smith

#include <cstdint>
#include <cstdio>
#include <cinttypes>

namespace bitcompactor
{
    template <typename T>
    T read_bits(const void *p, int first, int last)
    {
         int bits = last - first + 1;
         int offset = first;
         T dat = 0;
         const std::uint8_t *src = (std::uint8_t *)p;

         src += (offset/8);
         offset -= (offset/8) * 8;

         if (offset > 0) {
                dat |= *src >> offset;
                if (bits < 8) {
                     dat &= ((1 << bits) - 1);
                }
                src++;
                offset = (8 - offset);
                bits -= offset;
         }

         while (bits >= 8) {
                dat |= *src << offset;
                src++;
                offset += 8;
                bits -= 8;
         }

         if (bits > 0) {
                dat |= (*src << offset) & (((1 << bits) - 1) << offset);
         }

         return dat;
    }

    // returns words written (characters)
    int translate(void *data_ptr, const int data_bits, char *output, const char *alphabet, const int word_bits)
    {
        typedef std::uint32_t T;
        int offset = 0;
        for (int i = 0; i < data_bits; i += word_bits) {
            T word = read_bits<T>(data_ptr, i, i + word_bits - 1);
            output[offset++] = alphabet[word];
        }
        // add null
        output[offset] = 0;
        return offset;
    }
}

int main(int argc, char **argv)
{
    const char *alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ012345";
    // Oooh fabulous arms in the air, wiggle your hands and fingers
    std::uint64_t fabulous_data[2] =
    {
        0xDEADBEEFFEEDF00D,
        // padding, translate() should/could if I wasn't lazy
        0,
    };
    // DANGEROUS! ... my middle name is Danger ...
    // that's right, dr. Derek D. Danger Denkins ... -Smithe
    char output_string[128];
    int output_words = bitcompactor::translate(fabulous_data, 64, output_string, alphabet, 5);

    std::printf("FABULOUS!!! ... no wait ...\n");
    std::printf("fabulous_data = %" SCNxFAST64 "\n", fabulous_data[0]);
    std::printf("Fabulalphabet = %s\n", alphabet);
    std::printf("output_words = %i\n", output_words);
    std::printf("output_string = \"%s\"\n", output_string);

    // twas all for naught
    return 0;
}