132 lines
3.7 KiB
C++
132 lines
3.7 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2011-2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_BITWISE_HPP
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#define CRUFT_UTIL_BITWISE_HPP
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#include "types/bits.hpp"
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#include "debug.hpp"
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#include <type_traits>
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#include <cstdint>
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namespace cruft {
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///////////////////////////////////////////////////////////////////////////
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/// Rotate `value` left by `magnitude` bits.
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///
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/// `magnitude` must not be greater than the bit count of `value`.
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template <typename T>
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constexpr T
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rotatel [[gnu::pure]] (const T value, std::size_t magnitude)
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{
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CHECK_LE (magnitude, sizeof (value) * 8);
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return (value << magnitude) | (value >> (sizeof (value) * 8 - magnitude));
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}
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///------------------------------------------------------------------------
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/// Rotate `value` right by `magnitude` bits.
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///
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/// `magnitude` must not be greater than the bit count of `value`.
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template <typename T>
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constexpr T
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rotater [[gnu::pure]] (const T value, std::size_t magnitude)
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{
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CHECK_LE (magnitude, sizeof (value) * 8);
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return (value >> magnitude) | (value << (sizeof (value) * 8 - magnitude));
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}
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///////////////////////////////////////////////////////////////////////////
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/// Reverse the order of bits in the supplied value.
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///
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/// Adapted from 'bit twiddling hacks'
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template <typename T>
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constexpr
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std::enable_if_t<std::is_integral<T>::value, T>
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reverse (T src)
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{
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T dst = src; // dst will be reversed bits of v; first get LSB of v
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int bits = sizeof (src) * 8 - 1; // extra shift needed at end
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for (src >>= 1; src; src >>= 1) {
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dst <<= 1;
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dst |= src & 1;
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bits--;
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}
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dst <<= bits; // shift when src's highest bits are zero
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return dst;
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}
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///////////////////////////////////////////////////////////////////////////
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/// Reverse the order of bits in the supplied value.
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///
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/// Adapted from 'bit twiddling hacks'
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template <>
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constexpr
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uint8_t
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reverse (uint8_t val)
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{
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return ((val * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
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}
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///////////////////////////////////////////////////////////////////////////
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/// Calculates the number of bits that are set.
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constexpr unsigned
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popcount (unsigned t)
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{
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return __builtin_popcount (t);
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}
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///------------------------------------------------------------------------
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/// Calculates the number of bits that are set.
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constexpr unsigned long
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popcount (unsigned long t)
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{
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return __builtin_popcountl (t);
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}
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///------------------------------------------------------------------------
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/// Calculates the number of bits that are set.
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constexpr unsigned long long
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popcount (unsigned long long t)
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{
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return __builtin_popcountll (t);
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}
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///////////////////////////////////////////////////////////////////////////
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/// returns the integral value composed of the bits from `val' in the
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/// inclusive range [lo, hi].
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template <typename ValueT, typename IndexT>
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constexpr ValueT
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from_bits (ValueT val, IndexT hi, IndexT lo)
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{
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CHECK_LT (hi, IndexT (sizeof (ValueT) * 8));
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CHECK_LT (lo, IndexT (sizeof (ValueT) * 8));
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CHECK_GE (hi, 0);
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CHECK_GE (lo, 1);
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CHECK_GE (hi, lo);
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ValueT zero = 0;
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ValueT ones = ~zero;
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return (val >> lo) & (ones >> (sizeof (ValueT) * 8 - (hi - lo + 1)));
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}
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}
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#endif
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