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>
*/
#ifndef CRUFT_UTIL_BITWISE_HPP
#define CRUFT_UTIL_BITWISE_HPP
#include "types/bits.hpp"
#include "debug.hpp"
#include <type_traits>
#include <cstdint>
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namespace cruft {
const uint8_t BITMASK_1BITS = 0x01;
const uint8_t BITMASK_2BITS = 0x03;
const uint8_t BITMASK_3BITS = 0x07;
const uint8_t BITMASK_4BITS = 0x0F;
const uint8_t BITMASK_5BITS = 0x1F;
const uint8_t BITMASK_6BITS = 0x3F;
const uint8_t BITMASK_7BITS = 0x7F;
const uint8_t BITMASK_8BITS = 0xFF;
///////////////////////////////////////////////////////////////////////////
template <typename T>
constexpr T
rotatel [[gnu::pure]] (const T value, std::size_t magnitude)
{
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return (value << magnitude) | (value >> (sizeof (value) * 8 - magnitude));
}
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template <typename T>
constexpr T
rotater [[gnu::pure]] (const T value, std::size_t magnitude)
{
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return (value >> magnitude) | (value << (sizeof (value) * 8 - magnitude));
}
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///////////////////////////////////////////////////////////////////////////
// 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;
}
///////////////////////////////////////////////////////////////////////////
// adapted from 'bit twiddling hacks'
template <>
constexpr
uint8_t
reverse (uint8_t val)
{
return ((val * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
}
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///////////////////////////////////////////////////////////////////////////
template <
typename T,
typename = std::enable_if_t<
std::is_integral_v<T>
>
>
constexpr T
popcount (T t)
{
return __builtin_popcount (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)));
}
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}
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#endif