Base64.cxx

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#include "utils/Base64.hxx"
 
#include <stdint.h>
#include "utils/macros.h"
 
static const char nib64[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
std::string base64_encode(const std::string &binary)
{
    std::string ret;
    ret.reserve((binary.size() + 2) / 3 * 4);
    unsigned ofs = 0;
    while (ofs + 3 <= binary.size())
    {
        uint32_t d = (((uint8_t)binary[ofs]) << 16) //
            | (((uint8_t)binary[ofs + 1]) << 8)     //
            | (((uint8_t)binary[ofs + 2]));
        ret.push_back(nib64[(d >> 18) & 63]);
        ret.push_back(nib64[(d >> 12) & 63]);
        ret.push_back(nib64[(d >> 6) & 63]);
        ret.push_back(nib64[(d >> 0) & 63]);
        ofs += 3;
    }
    if (ofs + 1 == binary.size())
    {
        uint32_t d = (((uint8_t)binary[ofs]) << 16);
        ret.push_back(nib64[(d >> 18) & 63]);
        ret.push_back(nib64[(d >> 12) & 63]);
        ret.push_back('=');
        ret.push_back('=');
    }
    else if (ofs + 2 == binary.size())
    {
        uint32_t d = (((uint8_t)binary[ofs]) << 16) //
            | (((uint8_t)binary[ofs + 1]) << 8);
        ret.push_back(nib64[(d >> 18) & 63]);
        ret.push_back(nib64[(d >> 12) & 63]);
        ret.push_back(nib64[(d >> 6) & 63]);
        ret.push_back('=');
    }
    return ret;
}
 
unsigned nib64_to_byte(char c)
{
    switch (c)
    {
        case '=':
            return 64;
        case '-':
        case '+':
            return 62;
        case '_':
        case '/':
            return 63;
        default:
            break;
    }
    if ('A' <= c && c <= 'Z')
    {
        return c - 'A';
    }
    if ('a' <= c && c <= 'z')
    {
        return c - 'a' + 26;
    }
    if ('0' <= c && c <= '9')
    {
        return c - '0' + 52;
    }
    return 65;
}
 
bool base64_decode(const std::string &base64, std::string *data)
{
    HASSERT(data);
    data->clear();
    unsigned a = 0;
    unsigned have = 0; // how many bits we have in the accumulator
    unsigned ofs = 0;  // next input byte.
    while (ofs < base64.size())
    {
        int nib = nib64_to_byte(base64[ofs++]);
        if (nib >= 65)
            return false;
        if (nib == 64)
            return true;
        a <<= 6;
        a |= (nib & 63);
        have += 6;
        if (have >= 8)
        {
            data->push_back((char)((a >> (have - 8)) & 0xff));
            have -= 8;
        }
    }
    return true;
}