ollama/llama/base64.hpp

/*
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*/

#ifndef PUBLIC_DOMAIN_BASE64_HPP_
#define PUBLIC_DOMAIN_BASE64_HPP_

#include <cstdint>
#include <iterator>
#include <stdexcept>
#include <string>

class base64_error : public std::runtime_error
{
public:
    using std::runtime_error::runtime_error;
};

class base64
{
public:
    enum class alphabet
    {
        /** the alphabet is detected automatically */
        auto_,
        /** the standard base64 alphabet is used */
        standard,
        /** like `standard` except that the characters `+` and `/` are replaced by `-` and `_` respectively*/
        url_filename_safe
    };

    enum class decoding_behavior
    {
        /** if the input is not padded, the remaining bits are ignored */
        moderate,
        /** if a padding character is encounter decoding is finished */
        loose
    };

    /**
     Encodes all the elements from `in_begin` to `in_end` to `out`.

     @warning The source and destination cannot overlap. The destination must be able to hold at least
     `required_encode_size(std::distance(in_begin, in_end))`, otherwise the behavior depends on the output iterator.

     @tparam Input_iterator the source; the returned elements are cast to `std::uint8_t` and should not be greater than
     8 bits
     @tparam Output_iterator the destination; the elements written to it are from the type `char`
     @param in_begin the beginning of the source
     @param in_end the ending of the source
     @param out the destination iterator
     @param alphabet which alphabet should be used
     @returns the iterator to the next element past the last element copied
     @throws see `Input_iterator` and `Output_iterator`
    */
    template<typename Input_iterator, typename Output_iterator>
    static Output_iterator encode(Input_iterator in_begin, Input_iterator in_end, Output_iterator out,
                                  alphabet alphabet = alphabet::standard)
    {
        constexpr auto pad = '=';
        const char* alpha  = alphabet == alphabet::url_filename_safe
                                ? "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
                                : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

        while (in_begin != in_end) {
            std::uint8_t i0 = 0, i1 = 0, i2 = 0;

            // first character
            i0 = static_cast<std::uint8_t>(*in_begin);
            ++in_begin;

            *out = alpha[i0 >> 2 & 0x3f];
            ++out;

            // part of first character and second
            if (in_begin != in_end) {
                i1 = static_cast<std::uint8_t>(*in_begin);
                ++in_begin;

                *out = alpha[((i0 & 0x3) << 4) | (i1 >> 4 & 0x0f)];
                ++out;
            } else {
                *out = alpha[(i0 & 0x3) << 4];
                ++out;

                // last padding
                *out = pad;
                ++out;

                // last padding
                *out = pad;
                ++out;

                break;
            }

            // part of second character and third
            if (in_begin != in_end) {
                i2 = static_cast<std::uint8_t>(*in_begin);
                ++in_begin;

                *out = alpha[((i1 & 0xf) << 2) | (i2 >> 6 & 0x03)];
                ++out;
            } else {
                *out = alpha[(i1 & 0xf) << 2];
                ++out;

                // last padding
                *out = pad;
                ++out;

                break;
            }

            // rest of third
            *out = alpha[i2 & 0x3f];
            ++out;
        }

        return out;
    }
    /**
     Encodes a string.

     @param str the string that should be encoded
     @param alphabet which alphabet should be used
     @returns the encoded base64 string
     @throws see base64::encode()
    */
    static std::string encode(const std::string& str, alphabet alphabet = alphabet::standard)
    {
        std::string result;

        result.reserve(required_encode_size(str.length()) + 1);

        encode(str.begin(), str.end(), std::back_inserter(result), alphabet);

        return result;
    }
    /**
     Encodes a char array.

     @param buffer the char array
     @param size the size of the array
     @param alphabet which alphabet should be used
     @returns the encoded string
    */
    static std::string encode(const char* buffer, std::size_t size, alphabet alphabet = alphabet::standard)
    {
        std::string result;

        result.reserve(required_encode_size(size) + 1);

        encode(buffer, buffer + size, std::back_inserter(result), alphabet);

        return result;
    }
    /**
     Decodes all the elements from `in_begin` to `in_end` to `out`. `in_begin` may point to the same location as `out`,
     in other words: inplace decoding is possible.

     @warning The destination must be able to hold at least `required_decode_size(std::distance(in_begin, in_end))`,
     otherwise the behavior depends on the output iterator.

     @tparam Input_iterator the source; the returned elements are cast to `char`
     @tparam Output_iterator the destination; the elements written to it are from the type `std::uint8_t`
     @param in_begin the beginning of the source
     @param in_end the ending of the source
     @param out the destination iterator
     @param alphabet which alphabet should be used
     @param behavior the behavior when an error was detected
     @returns the iterator to the next element past the last element copied
     @throws base64_error depending on the set behavior
     @throws see `Input_iterator` and `Output_iterator`
    */
    template<typename Input_iterator, typename Output_iterator>
    static Output_iterator decode(Input_iterator in_begin, Input_iterator in_end, Output_iterator out,
                                  alphabet alphabet          = alphabet::auto_,
                                  decoding_behavior behavior = decoding_behavior::moderate)
    {
        //constexpr auto pad = '=';
        std::uint8_t last  = 0;
        auto bits          = 0;

        while (in_begin != in_end) {
            auto c = *in_begin;
            ++in_begin;

            if (c == '=') {
                break;
            }

            auto part = _base64_value(alphabet, c);

            // enough bits for one byte
            if (bits + 6 >= 8) {
                *out = (last << (8 - bits)) | (part >> (bits - 2));
                ++out;

                bits -= 2;
            } else {
                bits += 6;
            }

            last = part;
        }

        // check padding
        if (behavior != decoding_behavior::loose) {
            while (in_begin != in_end) {
                auto c = *in_begin;
                ++in_begin;

                if (c != '=') {
                    throw base64_error("invalid base64 character.");
                }
            }
        }

        return out;
    }
    /**
     Decodes a string.

     @param str the base64 encoded string
     @param alphabet which alphabet should be used
     @param behavior the behavior when an error was detected
     @returns the decoded string
     @throws see base64::decode()
    */
    static std::string decode(const std::string& str, alphabet alphabet = alphabet::auto_,
                              decoding_behavior behavior = decoding_behavior::moderate)
    {
        std::string result;

        result.reserve(max_decode_size(str.length()));

        decode(str.begin(), str.end(), std::back_inserter(result), alphabet, behavior);

        return result;
    }
    /**
     Decodes a string.

     @param buffer the base64 encoded buffer
     @param size the size of the buffer
     @param alphabet which alphabet should be used
     @param behavior the behavior when an error was detected
     @returns the decoded string
     @throws see base64::decode()
    */
    static std::string decode(const char* buffer, std::size_t size, alphabet alphabet = alphabet::auto_,
                              decoding_behavior behavior = decoding_behavior::moderate)
    {
        std::string result;

        result.reserve(max_decode_size(size));

        decode(buffer, buffer + size, std::back_inserter(result), alphabet, behavior);

        return result;
    }
    /**
     Decodes a string inplace.

     @param[in,out] str the base64 encoded string
     @param alphabet which alphabet should be used
     @param behavior the behavior when an error was detected
     @throws base64::decode_inplace()
    */
    static void decode_inplace(std::string& str, alphabet alphabet = alphabet::auto_,
                               decoding_behavior behavior = decoding_behavior::moderate)
    {
        str.resize(decode(str.begin(), str.end(), str.begin(), alphabet, behavior) - str.begin());
    }
    /**
     Decodes a char array inplace.

     @param[in,out] str the string array
     @param size the length of the array
     @param alphabet which alphabet should be used
     @param behavior the behavior when an error was detected
     @returns the pointer to the next element past the last element decoded
     @throws base64::decode_inplace()
    */
    static char* decode_inplace(char* str, std::size_t size, alphabet alphabet = alphabet::auto_,
                                decoding_behavior behavior = decoding_behavior::moderate)
    {
        return decode(str, str + size, str, alphabet, behavior);
    }
    /**
     Returns the required decoding size for a given size. The value is calculated with the following formula:

     $$
     \lceil \frac{size}{4} \rceil \cdot 3
     $$

     @param size the size of the encoded input
     @returns the size of the resulting decoded buffer; this the absolute maximum
    */
    static std::size_t max_decode_size(std::size_t size) noexcept
    {
        return (size / 4 + (size % 4 ? 1 : 0)) * 3;
    }
    /**
     Returns the required encoding size for a given size. The value is calculated with the following formula:

     $$
     \lceil \frac{size}{3} \rceil \cdot 4
     $$

     @param size the size of the decoded input
     @returns the size of the resulting encoded buffer
    */
    static std::size_t required_encode_size(std::size_t size) noexcept
    {
        return (size / 3 + (size % 3 ? 1 : 0)) * 4;
    }

private:
    static std::uint8_t _base64_value(alphabet& alphabet, char c)
    {
        if (c >= 'A' && c <= 'Z') {
            return c - 'A';
        } else if (c >= 'a' && c <= 'z') {
            return c - 'a' + 26;
        } else if (c >= '0' && c <= '9') {
            return c - '0' + 52;
        }

        // comes down to alphabet
        if (alphabet == alphabet::standard) {
            if (c == '+') {
                return 62;
            } else if (c == '/') {
                return 63;
            }
        } else if (alphabet == alphabet::url_filename_safe) {
            if (c == '-') {
                return 62;
            } else if (c == '_') {
                return 63;
            }
        } // auto detect
        else {
            if (c == '+') {
                alphabet = alphabet::standard;

                return 62;
            } else if (c == '/') {
                alphabet = alphabet::standard;

                return 63;
            } else if (c == '-') {
                alphabet = alphabet::url_filename_safe;

                return 62;
            } else if (c == '_') {
                alphabet = alphabet::url_filename_safe;

                return 63;
            }
        }

        throw base64_error("invalid base64 character.");
    }
};

#endif // !PUBLIC_DOMAIN_BASE64_HPP_