bitfield.hh

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#ifndef __BASE_BITFIELD_HH__
#define __BASE_BITFIELD_HH__

#include <inttypes.h>
#include <cassert>
#include <cstddef>
#include <type_traits>

extern const uint8_t reverseLookUpTable[];

inline uint64_t
mask(int nbits)
{
    return (nbits >= 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
}

template <class T>
inline
T
bits(T val, int first, int last)
{
    int nbits = first - last + 1;
    return (val >> last) & mask(nbits);
}

template <class T>
inline
T
bits(T val, int bit)
{
    return bits(val, bit, bit);
}

template <class T>
inline
T
mbits(T val, int first, int last)
{
    return val & (mask(first+1) & ~mask(last));
}

inline uint64_t
mask(int first, int last)
{
    return mbits((uint64_t)-1LL, first, last);
}

template <int N>
inline
uint64_t
sext(uint64_t val)
{
    int sign_bit = bits(val, N-1, N-1);
    return sign_bit ? (val | ~mask(N)) : val;
}

template <class T, class B>
inline
T
insertBits(T val, int first, int last, B bit_val)
{
    T t_bit_val = bit_val;
    T bmask = mask(first - last + 1) << last;
    return ((t_bit_val << last) & bmask) | (val & ~bmask);
}

template <class T, class B>
inline
T
insertBits(T val, int bit, B bit_val)
{
    return insertBits(val, bit, bit, bit_val);
}

template <class T, class B>
inline
void
replaceBits(T& val, int first, int last, B bit_val)
{
    val = insertBits(val, first, last, bit_val);
}

template <class T, class B>
inline
void
replaceBits(T& val, int bit, B bit_val)
{
    val = insertBits(val, bit, bit, bit_val);
}

template <class T>
T
reverseBits(T val, std::size_t size = sizeof(T))
{
    static_assert(std::is_integral<T>::value, "Expecting an integer type");

    assert(size <= sizeof(T));

    T output = 0;
    for (auto byte = 0; byte < size; byte++, val = static_cast<T>(val >> 8)) {
        output = (output << 8) | reverseLookUpTable[val & 0xFF];
    }

    return output;
}

inline
int
findMsbSet(uint64_t val) {
    int msb = 0;
    if (!val)
        return 0;
    if (bits(val, 63,32)) { msb += 32; val >>= 32; }
    if (bits(val, 31,16)) { msb += 16; val >>= 16; }
    if (bits(val, 15,8))  { msb += 8;  val >>= 8;  }
    if (bits(val, 7,4))   { msb += 4;  val >>= 4;  }
    if (bits(val, 3,2))   { msb += 2;  val >>= 2;  }
    if (bits(val, 1,1))   { msb += 1; }
    return msb;
}

inline int
findLsbSet(uint64_t val) {
    int lsb = 0;
    if (!val)
        return sizeof(val) * 8;
    if (!bits(val, 31,0)) { lsb += 32; val >>= 32; }
    if (!bits(val, 15,0)) { lsb += 16; val >>= 16; }
    if (!bits(val, 7,0))  { lsb += 8;  val >>= 8;  }
    if (!bits(val, 3,0))  { lsb += 4;  val >>= 4;  }
    if (!bits(val, 1,0))  { lsb += 2;  val >>= 2;  }
    if (!bits(val, 0,0))  { lsb += 1; }
    return lsb;
}

template <class T>
inline bool
isPow2(T v) {
   return (v & (v - 1)) == (T)0;
}

inline int
popCount(uint64_t val) {
#ifndef __has_builtin
    #define __has_builtin(foo) 0
#endif
#if defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
    return __builtin_popcountl(val);
#else
    const uint64_t m1 = 0x5555555555555555;  // ..010101b
    const uint64_t m2 = 0x3333333333333333;  // ..110011b
    const uint64_t m4 = 0x0f0f0f0f0f0f0f0f;  // ..001111b
    const uint64_t sum = 0x0101010101010101;

    val -= (val >> 1) & m1;               // 2 bits count -> 2 bits
    val = (val & m2) + ((val >> 2) & m2); // 4 bits count -> 4 bits
    val = (val + (val >> 4)) & m4;        // 8 bits count -> 8 bits
    return (val * sum) >> 56;             // horizontal sum
#endif // defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
}

inline uint64_t alignToPowerOfTwo(uint64_t val)
{
    val--;
    val |= val >> 1;
    val |= val >> 2;
    val |= val >> 4;
    val |= val >> 8;
    val |= val >> 16;
    val |= val >> 32;
    val++;

    return val;
};

inline int ctz32(uint32_t value)
{
    return value ? __builtin_ctzl(value) : 32;
}

inline int ctz64(uint64_t value)
{
    return value ? __builtin_ctzll(value) : 64;
}

#endif // __BASE_BITFIELD_HH__