libcruft-util/bitwise.hpp

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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright 2011-2018 Danny Robson <danny@nerdcruft.net>
*/
#pragma once
#include "types/bits.hpp"
#include "debug.hpp"
#include <type_traits>
#include <cstdint>
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namespace cruft {
///////////////////////////////////////////////////////////////////////////
/// Rotate `value` left by `magnitude` bits.
///
/// `magnitude` must not be greater than the bit count of `value`.
template <typename T>
constexpr T
rotatel [[gnu::pure]] (const T value, std::size_t magnitude)
{
CHECK_LE (magnitude, sizeof (value) * 8);
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return (value << magnitude) | (value >> (sizeof (value) * 8 - magnitude));
}
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///------------------------------------------------------------------------
/// Rotate `value` right by `magnitude` bits.
///
/// `magnitude` must not be greater than the bit count of `value`.
template <typename T>
constexpr T
rotater [[gnu::pure]] (const T value, std::size_t magnitude)
{
CHECK_LE (magnitude, sizeof (value) * 8);
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return (value >> magnitude) | (value << (sizeof (value) * 8 - magnitude));
}
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///////////////////////////////////////////////////////////////////////////
/// Reverse the order of bits in the supplied value.
///
/// Adapted from 'bit twiddling hacks'
template <typename T>
constexpr
std::enable_if_t<std::is_integral<T>::value, T>
reverse (T src)
{
T dst = src; // dst will be reversed bits of v; first get LSB of v
int bits = sizeof (src) * 8 - 1; // extra shift needed at end
for (src >>= 1; src; src >>= 1) {
dst <<= 1;
dst |= src & 1;
bits--;
}
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dst <<= bits; // shift when src's highest bits are zero
return dst;
}
///////////////////////////////////////////////////////////////////////////
/// Reverse the order of bits in the supplied value.
///
/// Adapted from 'bit twiddling hacks'
template <>
constexpr
uint8_t
reverse (uint8_t val)
{
return ((val * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
}
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///////////////////////////////////////////////////////////////////////////
/// Calculates the number of bits that are set.
constexpr unsigned
popcount (unsigned t)
{
return __builtin_popcount (t);
}
///------------------------------------------------------------------------
/// Calculates the number of bits that are set.
constexpr unsigned long
popcount (unsigned long t)
{
return __builtin_popcountl (t);
}
///------------------------------------------------------------------------
/// Calculates the number of bits that are set.
constexpr unsigned long long
popcount (unsigned long long t)
{
return __builtin_popcountll (t);
}
///////////////////////////////////////////////////////////////////////////
/// returns the integral value composed of the bits from `val' in the
/// inclusive range [lo, hi].
template <typename ValueT, typename IndexT>
constexpr ValueT
from_bits (ValueT val, IndexT hi, IndexT lo)
{
CHECK_LT (hi, IndexT (sizeof (ValueT) * 8));
CHECK_LT (lo, IndexT (sizeof (ValueT) * 8));
CHECK_GE (hi, 0);
CHECK_GE (lo, 1);
CHECK_GE (hi, lo);
ValueT zero = 0;
ValueT ones = ~zero;
return (val >> lo) & (ones >> (sizeof (ValueT) * 8 - (hi - lo + 1)));
}
/// A convenience wrapper that provides access to a range of bits in an
/// underlying integral value.
///
/// This class is most useful as part of a union where each has differing
/// offsets and sizes that cover the underlying type.
///
/// A conversion operator is supplied for accessing the bit value.
///
/// ValueT must support bit shifting and bitwise operators (primarily
/// bitwise and).
///
/// \tparam ValueT the underlying integral type
/// \tparam OffsetV the index of the first bit of the range (where 0 is
/// most significant)
/// \tparam SizeV the number of bits in the range. Must be strictly
/// positive.
template <
typename ValueT,
size_t OffsetV,
size_t SizeV
>
class bitfield {
public:
static_assert (SizeV > 0);
static_assert (OffsetV + SizeV <= sizeof (ValueT) * 8);
static_assert (sizeof (ValueT) == sizeof (bitfield));
decltype(auto)
operator+ () const { return +value; }
operator auto() const
{
auto const MASK = (1u << SizeV) - 1u;
auto const SHIFT = sizeof (ValueT) * 8 - OffsetV - SizeV;
return (value >> SHIFT) & MASK;
}
ValueT value;
};
template <typename ValueT, size_t Offset, size_t Size>
std::ostream& operator<< (std::ostream &os, bitfield<ValueT,Offset,Size> const &val)
{
return os << +ValueT(val);
}
}