// Copyright 2018-2022 David Robillard <d@drobilla.net>
// Copyright 2006-2007 Chris Hamilton <chamilton@cs.dal.ca>
// SPDX-License-Identifier: GPL-2.0-or-later

#ifndef CHILBERT_DETAIL_OPERATIONS_HPP
#define CHILBERT_DETAIL_OPERATIONS_HPP

#include "chilbert/detail/traits.hpp"
#include "chilbert/operators.hpp"

#ifdef _MSC_VER
#  include <immintrin.h>
#  include <intrin.h>
#endif

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

namespace chilbert {
namespace detail {

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

/// Reset all bits in `field`
template<typename T>
std::enable_if_t<is_bitvec_v<T>>
reset_bits(T& field)
{
  field.reset();
}

/// Return the `index`th bit in `field`
template<typename T>
std::enable_if_t<std::is_integral<T>::value, bool>
test_bit(const T& field, const size_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>
std::enable_if_t<is_bitvec_v<T>, bool>
test_bit(const T& field, const size_t index)
{
  return field.test(index);
}

/// Set the `index`th bit in `field`
template<typename T>
std::enable_if_t<std::is_integral<T>::value>
set_bit(T& field, const size_t index)
{
  assert(size_t(index) < sizeof(field) * CHAR_BIT);
  field |= (T{1} << index);
  assert(test_bit(field, index));
}

/// Set the `index`th bit in `field` to `value`
template<typename T>
std::enable_if_t<std::is_integral<T>::value>
set_bit(T& field, const size_t index, const bool value)
{
  assert(size_t(index) < sizeof(field) * CHAR_BIT);
  field ^= (-T{value} ^ field) & (T{1U} << index);
  assert(test_bit(field, index) == value);
}

/// Set the `index`th bit in `field`
template<typename T>
std::enable_if_t<is_bitvec_v<T>>
set_bit(T& field, const size_t index)
{
  field.set(index);
}

/// Set the `index`th bit in `field` to `value`
template<typename T>
std::enable_if_t<is_bitvec_v<T>>
set_bit(T& field, const size_t index, const bool value)
{
  field.set(index, value);
}

#ifdef _MSC_VER

inline uint32_t
pop_count(const uint32_t field)
{
  return __popcnt(field);
}

inline uint64_t
pop_count(const uint64_t field)
{
  return __popcnt64(field);
}

#else

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

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

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

#endif

#ifdef _MSC_VER

inline uint32_t
find_first(const uint32_t field)
{
  return field ? 1U + _tzcnt_u32(field) : 0U;
}

inline uint64_t
find_first(const uint64_t field)
{
  return field ? 1U + _tzcnt_u64(field) : 0U;
}

#else

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

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

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

#endif

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

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

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

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

} // namespace detail
} // namespace chilbert

#endif