Atmosphere/libraries/libvapours/include/vapours/util/util_bitutil.hpp

/*
 * Copyright (c) Atmosphère-NX
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once
#include <vapours/common.hpp>
#include <vapours/assert.hpp>

namespace ams::util {

    namespace impl {

        template<size_t N>
        constexpr inline size_t Log2 = Log2<N / 2> + 1;

        template<>
        constexpr inline size_t Log2<1> = 0;

    }

    template<std::integral T>
    constexpr inline T ReverseBits(T x, int sw_bits = 1, int swar_words = 1) {
        /* Check pre-conditions. */
        AMS_ASSERT(0 <= swar_words && swar_words < (BITSIZEOF(T) + 1));
        AMS_ASSERT(BITSIZEOF(T) % swar_words == 0);
        AMS_ASSERT(0 <= sw_bits && sw_bits < ((BITSIZEOF(T) / swar_words) + 1));
        AMS_ASSERT((BITSIZEOF(T) / swar_words) % sw_bits == 0);

        using U = typename std::make_unsigned<T>::type;
        const int word_size = BITSIZEOF(T) / swar_words;
        const int k = word_size - sw_bits;

        U u = std::bit_cast<U, T>(x);
        for (int i = 1; i < BITSIZEOF(T); i <<= 1) {
            const U mask  = static_cast<U>(static_cast<U>(-1) / ((static_cast<U>(1) << i) + 1));

            if (k & i) {
                u = static_cast<U>(((u & mask) << i) | ((u & static_cast<U>(~mask)) >> i));
            }
        }

        return std::bit_cast<T, U>(u);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T ReverseBytes(T x, int sw_bytes = 1, int swar_words = 1) {
        return ReverseBits(x, sw_bytes * BITSIZEOF(u8), swar_words);
    }

    template<typename T = u64, typename ...Args> requires std::integral<T>
    constexpr ALWAYS_INLINE T CombineBits(Args... args) {
        return (... | (T(1u) << args));
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T ResetLeastSignificantOneBit(T x) {
        return x & (x - 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T SetLeastSignificantZeroBit(T x) {
        return x | (x + 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T ResetTrailingOnes(T x) {
        return x & (x + 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T SetTrailingZeros(T x) {
        return x | (x - 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T LeastSignificantOneBit(T x) {
        return x & ~(x - 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T LeastSignificantZeroBit(T x) {
        return ~x & (x + 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T MaskTrailingZeros(T x) {
        return (~x) & (x - 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T MaskTrailingOnes(T x) {
        return x & ~(x + 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T MaskTrailingZerosAndLeastSignificantOneBit(T x) {
        return x ^ (x - 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T MaskTrailingOnesAndLeastSignificantZeroBit(T x) {
        return x ^ (x + 1);
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE int PopCount(T x) {
        using U = typename std::make_unsigned<T>::type;
        U u = static_cast<U>(x);

        if (std::is_constant_evaluated()) {
            /* https://en.wikipedia.org/wiki/Hamming_weight */
            constexpr U m1 = U(-1) / 0x03;
            constexpr U m2 = U(-1) / 0x05;
            constexpr U m4 = U(-1) / 0x11;

            u = static_cast<U>(u - ((u >> 1) & m1));
            u = static_cast<U>((u & m2) + ((u >> 2) & m2));
            u = static_cast<U>((u + (u >> 4)) & m4);

            for (size_t i = 0; i < impl::Log2<sizeof(T)>; ++i) {
                const size_t shift = (0x1 << i) * BITSIZEOF(u8);
                u += u >> shift;
            }

            return static_cast<int>(u & 0x7Fu);
        } else {
            if constexpr (std::is_same<U, unsigned long long>::value) {
                return __builtin_popcountll(u);
            } else if constexpr (std::is_same<U, unsigned long>::value) {
                return __builtin_popcountl(u);
            } else {
                static_assert(sizeof(U) <= sizeof(unsigned int));
                return __builtin_popcount(static_cast<unsigned int>(u));
            }
        }
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE int CountLeadingZeros(T x) {
        if (std::is_constant_evaluated()) {
            for (size_t i = 0; i < impl::Log2<BITSIZEOF(T)>; ++i) {
                const size_t shift = (0x1 << i);
                x |= x >> shift;
            }
            return PopCount(static_cast<T>(~x));
        } else {
            using U = typename std::make_unsigned<T>::type;

            if (const U u = static_cast<U>(x); u != 0) {
                if constexpr (std::is_same<U, unsigned long long>::value) {
                    return __builtin_clzll(u);
                } else if constexpr (std::is_same<U, unsigned long>::value) {
                    return __builtin_clzl(u);
                }  else if constexpr(std::is_same<U, unsigned int>::value) {
                    return __builtin_clz(u);
                } else {
                    static_assert(sizeof(U) < sizeof(unsigned int));
                    constexpr size_t BitDiff = BITSIZEOF(unsigned int) - BITSIZEOF(U);
                    return __builtin_clz(static_cast<unsigned int>(u)) - BitDiff;
                }
            } else {
                return BITSIZEOF(U);
            }
        }
    }

    static_assert(CountLeadingZeros(~static_cast<u64>(0)) == 0);
    static_assert(CountLeadingZeros(static_cast<u64>(1) << 5) == BITSIZEOF(u64) - 1 - 5);
    static_assert(CountLeadingZeros(static_cast<u64>(0)) == BITSIZEOF(u64));

    template<std::integral T>
    constexpr ALWAYS_INLINE int CountTrailingZeros(T x) {
        if (std::is_constant_evaluated()) {
            auto count = 0;
            for (size_t i = 0; i < BITSIZEOF(T) && (x & 1) == 0; ++i) {
                x >>= 1;
                ++count;
            }
            return count;
        } else {
            using U = typename std::make_unsigned<T>::type;
            if (const U u = static_cast<U>(x); u != 0) {
                if constexpr (std::is_same<U, unsigned long long>::value) {
                    return __builtin_ctzll(u);
                } else if constexpr (std::is_same<U, unsigned long>::value) {
                    return __builtin_ctzl(u);
                }  else if constexpr(std::is_same<U, unsigned int>::value) {
                    return __builtin_ctz(u);
                } else {
                    static_assert(sizeof(U) < sizeof(unsigned int));
                    return __builtin_ctz(static_cast<unsigned int>(u));
                }
            } else {
                return BITSIZEOF(U);
            }
        }
    }

    static_assert(CountTrailingZeros(~static_cast<u64>(0)) == 0);
    static_assert(CountTrailingZeros(static_cast<u64>(1) << 5) == 5);
    static_assert(CountTrailingZeros(static_cast<u64>(0)) == BITSIZEOF(u64));

    template<std::integral T>
    constexpr ALWAYS_INLINE bool IsPowerOfTwo(T x) {
        return x > 0 && ResetLeastSignificantOneBit(x) == 0;
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T CeilingPowerOfTwo(T x) {
        AMS_ASSERT(x > 0);
        return T(1) << (BITSIZEOF(T) - CountLeadingZeros(T(x - 1)));
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T FloorPowerOfTwo(T x) {
        AMS_ASSERT(x > 0);
        return T(1) << (BITSIZEOF(T) - CountLeadingZeros(x) - 1);
    }

    template<std::integral T, std::integral U>
    constexpr ALWAYS_INLINE T DivideUp(T v, U d) {
        using Unsigned = typename std::make_unsigned<U>::type;
        using Sum      = decltype(T{0} + U{0});

        #if defined(ATMOSPHERE_IS_STRATOSPHERE)
        AMS_ASSERT(v >= 0);
        AMS_ASSERT(d > 0);
        AMS_ASSERT(static_cast<Sum>(v) <= (std::numeric_limits<Sum>::max() - static_cast<Sum>(d) + static_cast<Sum>(1)));
        #endif

        const Unsigned add = static_cast<Unsigned>(d) - 1;
        return static_cast<T>((static_cast<Sum>(v) + static_cast<Sum>(add)) / static_cast<Sum>(d));
    }

    template<std::integral T, T N, T D>
    constexpr ALWAYS_INLINE T ScaleByConstantFactorUp(const T V) {
        /* Multiplying and dividing by large numerator/denominator can cause error to be introduced. */
        /* This algorithm multiples/divides in stages, so as to mitigate this (particularly with large denominator). */

        /* Justification for the algorithm.                                                                         */
        /* Calculate: (V * N) / D                                                                                   */
        /*          = (Quot_V * D + Rem_V) * (Quot_N * D + Rem_N) / D                                               */
        /*          = (D^2 * (Quot_V * Quot_N) + D * (Quot_V * Rem_N + Rem_V * Quot_N) + Rem_V * Rem_N) / D         */
        /*          = (D * Quot_V * Quot_N) + (Quot_V * Rem_N) + (Rem_V * Quot_N) + ((Rem_V * Rem_N) / D)           */

        /* Calculate quotients/remainders. */
        const     T Quot_V = V / D;
        const     T Rem_V  = V % D;
        constexpr T Quot_N = N / D;
        constexpr T Rem_N  = N % D;

        /* Calculate the remainder multiplication, rounding up. */
        const T rem_mult = ((Rem_V * Rem_N) + (D - 1)) / D;

        /* Calculate results. */
        return (D * Quot_N * Quot_V) + (Quot_V * Rem_N) + (Rem_V * Quot_N) + rem_mult;
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T RotateLeft(T v, int n) {
        using Unsigned = typename std::make_unsigned<T>::type;
        static_assert(sizeof(Unsigned) == sizeof(T));

        return static_cast<T>(std::rotl<Unsigned>(static_cast<Unsigned>(v), n));
    }

    template<std::integral T>
    constexpr ALWAYS_INLINE T RotateRight(T v, int n) {
        using Unsigned = typename std::make_unsigned<T>::type;
        static_assert(sizeof(Unsigned) == sizeof(T));

        return static_cast<T>(std::rotr<Unsigned>(static_cast<Unsigned>(v), n));
    }

}