bitoperations.h

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#pragma once
#include <array>
#include <bit>
#include <cstdint>
#include <ranges>
 
#include "storm/utility/macros.h"
 
namespace storm::utility {
 
template<typename T>
inline T byteSwap(T const t) {
    // Note: c++23's std::bit_cast does not allow floating point types. Potentially because they don't have a unique object representation (NaN).
    static_assert(std::has_unique_object_representations_v<T> || std::is_same_v<T, double> || std::is_same_v<T, float>, "T may not have padding bits");
    auto value_representation = std::bit_cast<std::array<std::byte, sizeof(T)>>(t);
    std::ranges::reverse(value_representation);
    return std::bit_cast<T>(value_representation);
}
 
template<typename T, bool ReverseBytes = true>
inline T reverseBits(T const t) {
    // lookup table to quickly reverse the bits in a byte, taken from https://stackoverflow.com/a/2606268
    static const unsigned char table[] = {
        0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0, 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
        0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
        0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
        0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
        0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
        0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
        0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
        0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
        0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
        0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
        0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff};
 
    static_assert(std::has_unique_object_representations_v<T> || std::is_same_v<T, double> || std::is_same_v<T, float>, "T may not have padding bits");
    auto value_representation = std::bit_cast<std::array<unsigned char, sizeof(T)>>(t);
    if constexpr (ReverseBytes) {
        std::ranges::reverse(value_representation);  // reverse the bytes
    }
    std::ranges::transform(value_representation, value_representation.begin(),
                           [](unsigned char byte) { return table[byte]; });  // reverse the bits in each byte
    return std::bit_cast<T>(value_representation);
}
 
}  // namespace storm::utility
 
inline uint64_t smallestIntWithNBitsSet(uint64_t n) {
    STORM_LOG_ASSERT(n < 64, "Input is too large.");
    if (n == 0)
        return 0;
    return (1ul << n) - 1;
}
 
inline uint64_t nextBitPermutation(uint64_t v) {
    if (v == 0)
        return 0;
    uint64_t t = (v | (v - 1)) + 1;
    return t | ((((t & -t) / (v & -v)) >> 1) - 1);
}