/*
  Copyright (C) 2018 David Robillard <d@drobilla.net>
  Copyright (C) 2006-2007 Chris Hamilton <chamilton@cs.dal.ca>

  This program is free software: you can redistribute it and/or modify it under
  the terms of the GNU General Public License as published by the Free Software
  Foundation, either version 2 of the License, or (at your option) any later
  version.

  This program is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
  details.

  You should have received a copy of the GNU General Public License along with
  this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#ifndef CHILBERT_OPERATIONS_HPP
#define CHILBERT_OPERATIONS_HPP

#include <cassert>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <type_traits>

namespace chilbert {

/// IntegralIndex<T> only exists if T is integral
template <typename T>
using IntegralIndex = std::enable_if_t<std::is_integral<T>::value, size_t>;

/// BitsetIndex<T> only exists if T is not integral (must be a bitset)
template <typename T>
using BitsetIndex = std::enable_if_t<!std::is_integral<T>::value, size_t>;

/// Reset all bits in `field`
template <typename T>
std::enable_if_t<std::is_integral<T>::value>
resetBits(T& field)
{
	field = static_cast<T>(0);
}

/// Reset all bits in `field`
template <typename T>
std::enable_if_t<!std::is_integral<T>::value>
resetBits(T& field)
{
	field.reset();
}

/// Return the `index`th bit in `field`
template <typename T>
bool
testBit(const T& field, const IntegralIndex<T> index)
{
	assert(size_t(index) < sizeof(field) * CHAR_BIT);
	return field & (T{1} << index);
}

/// Return the `index`th bit in `field`
template <typename T>
bool
testBit(const T& field, const BitsetIndex<T> index)
{
	return field.test(index);
}

/// Set the `index`th bit in `field`
template <typename T>
void
setBit(T& field, const IntegralIndex<T> index)
{
	assert(size_t(index) < sizeof(field) * CHAR_BIT);
	field |= (T{1} << index);
	assert(testBit(field, index));
}

/// Set the `index`th bit in `field` to `value`
template <typename T>
void
setBit(T& field, const IntegralIndex<T> index, const bool value)
{
	assert(size_t(index) < sizeof(field) * CHAR_BIT);
	field ^= (-T{value} ^ field) & (T{1U} << index);
	assert(testBit(field, index) == value);
}

/// Set the `index`th bit in `field`
template <typename T>
void
setBit(T& field, const BitsetIndex<T> index)
{
	field.set(index);
}

/// Set the `index`th bit in `field` to `value`
template <typename T>
void
setBit(T& field, const BitsetIndex<T> index, const bool value)
{
	field.set(index, value);
}

/// Return 1 + the index of the least significant 1-bit of `field`, or zero
template <typename T>
int pop_count(const T& field);

template <>
int
pop_count<unsigned long>(const unsigned long& field)
{
	return __builtin_popcountl(field);
}

template <>
int
pop_count<unsigned long long>(const unsigned long long& field)
{
	return __builtin_popcountll(field);
}

/// Return 1 + the index of the least significant 1-bit of `field`, or zero
template <typename T>
int ffs(const T field);

template <>
int
ffs<unsigned long>(const unsigned long field)
{
	return __builtin_ffsl(static_cast<long>(field));
}

template <>
int
ffs<unsigned long long>(const unsigned long long field)
{
	return __builtin_ffsll(static_cast<long long>(field));
}

/// Calculates the Gray Code of `value` in place
template <typename T>
std::enable_if_t<!std::is_integral<T>::value> grayCode(T& value);

/// Implementation of grayCode for any integral type
template <typename T>
std::enable_if_t<std::is_integral<T>::value>
grayCode(T& value)
{
	value ^= (value >> 1);
}

/// Calculates the inverse Gray Code of `value` in place
template <typename T>
std::enable_if_t<!std::is_integral<T>::value> grayCodeInv(T& value);

/// Implementation of grayCodeInv for any integral type
template <typename T>
std::enable_if_t<std::is_integral<T>::value>
grayCodeInv(T& value)
{
	for (T shift = 1; shift < sizeof(T) * CHAR_BIT; shift <<= 1) {
		value ^= (value >> shift);
	}
}

} // namespace chilbert

#endif