construct/include/ircd/b64.h

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_B64_H

namespace ircd::b64
{
	IRCD_EXCEPTION(ircd::error, error)
	IRCD_EXCEPTION(error, invalid_encoding)

	using dictionary_element = int;
	using dictionary = dictionary_element[64];

	extern const dictionary
	dict_rfc1421,   // [62] = '+', [63] = '/'
	dict_rfc3501,   // [62] = '+', [63] = ','
	dict_rfc4648;   // [62] = '-', [63] = '_'

	static const auto
	&standard { dict_rfc1421 },
	&mailbox  { dict_rfc3501 },
	&urlsafe  { dict_rfc4648 };

	constexpr size_t decode_size(const size_t) noexcept;
	constexpr size_t encode_size(const size_t) noexcept;
	constexpr size_t encode_unpadded_size(const size_t) noexcept;

	size_t decode_size(const string_view &in) noexcept;
	size_t encode_size(const const_buffer &in) noexcept;
	size_t encode_unpadded_size(const const_buffer &in) noexcept;

	const_buffer decode(const mutable_buffer &out, const string_view &in);

	template<const dictionary & = dict_rfc1421>
	string_view encode(const mutable_buffer &out, const const_buffer &in) noexcept;

	template<const dictionary & = dict_rfc1421>
	string_view encode_unpadded(const mutable_buffer &out, const const_buffer &in) noexcept;
}

inline size_t
ircd::b64::encode_unpadded_size(const const_buffer &in)
noexcept
{
	return encode_unpadded_size(size(in));
}

inline size_t
ircd::b64::encode_size(const const_buffer &in)
noexcept
{
	return encode_size(size(in));
}

inline size_t
ircd::b64::decode_size(const string_view &in)
noexcept
{
	const size_t pads
	{
		endswith_count(in, '=')
	};

	return decode_size(size(in) - pads);
}

constexpr size_t
ircd::b64::encode_unpadded_size(const size_t in)
noexcept
{
	constexpr long double A
	{
		4.0L / 3.0L
	};

	const auto e
	{
		in % 3 != 0
	};

	return A * in + e;
}

constexpr size_t
ircd::b64::encode_size(const size_t in)
noexcept
{
	const auto base
	{
		encode_unpadded_size(in)
	};

	const size_t pads
	{
		(3 - in % 3) % 3
	};

	return base + pads;
}

constexpr size_t
ircd::b64::decode_size(const size_t in)
noexcept
{
	constexpr long double A
	{
		3.0L / 4.0L
	};

	return A * in;
}