libcruft-util/bitwise.hpp

/*
 * 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>


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)
    {
        return (value << magnitude) | (value >> (sizeof (value) * 8 - magnitude));
    }


    template <typename T>
    constexpr T
    rotater [[gnu::pure]] (const T value, std::size_t magnitude)
    {
        return (value >> magnitude) | (value << (sizeof (value) * 8 - magnitude));
    }


    ///////////////////////////////////////////////////////////////////////////
    // 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--;
        }

        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;
    }


    ///////////////////////////////////////////////////////////////////////////
    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)));
    }
}

#endif