BitOps.h

#ifndef ROSE_BitOps_H
#define ROSE_BitOps_H

#include <Sawyer/Assert.h>
#include <Sawyer/Optional.h>

namespace Rose {

namespace BitOps {

template<typename Unsigned>
inline size_t nBits(Unsigned = Unsigned(0)) {
    return 8*sizeof(Unsigned);
}

template<typename Unsigned>
inline Unsigned all(bool b = true) {
    return Unsigned(0) - Unsigned(b ? 1 : 0);
}

template<typename Unsigned> inline Unsigned lowMask(size_t n);

template<typename Unsigned>
inline Unsigned allLsb(Unsigned src, size_t w, bool b = true) {
    ASSERT_require(w <= nBits(src));
    if (b) {
        return src | lowMask<Unsigned>(w);
    } else {
        return src & ~lowMask<Unsigned>(w);
    }
}

template<typename Unsigned>
inline Unsigned lowMask(size_t n) {
    return n >= nBits<Unsigned>() ? all<Unsigned>(true) : (Unsigned(1) << n) - Unsigned(1);
}

template<typename Unsigned>
inline Unsigned highMask(size_t n) {
    return n >= nBits<Unsigned>() ? all<Unsigned>(true) : lowMask<Unsigned>(n) << (nBits<Unsigned>() - n);
}

template<typename Unsigned>
inline Unsigned select(Unsigned cond, Unsigned a, Unsigned b) {
    return (a & cond) | (b & ~cond);
}

template<typename Unsigned>
inline Unsigned shiftLeft(Unsigned src, size_t n, bool b = false) {
    if (n >= nBits(src)) {
        return all<Unsigned>(b);
    } else {
        return Unsigned(src << n) | (all<Unsigned>(b) & lowMask<Unsigned>(n));
    }
}

template<typename Unsigned>
inline Unsigned shiftLeftLsb(Unsigned src, size_t w, size_t n, bool b = false) {
    ASSERT_require(w <= nBits(src));
    if (n >= w) {
        return allLsb(src, w, b);
    } else {
        return select(lowMask<Unsigned>(w), shiftLeft(src, n, b), src);
    }
}

template<typename Unsigned>
inline Unsigned shiftRight(Unsigned src, size_t n, bool b = false) {
    if (n >= nBits(src)) {
        return all<Unsigned>(b);
    } else {
        return Unsigned(src >> n) | (all<Unsigned>(b) & highMask<Unsigned>(n));
    }
}

template<typename Unsigned>
inline Unsigned shiftRightLsb(Unsigned src, size_t w, size_t n, bool b = false) {
    ASSERT_require(w <= nBits(src));
    if (n >= w) {
        return allLsb(src, w, b);
    } else {
        return select(lowMask<Unsigned>(w), shiftRight(src & lowMask<Unsigned>(w), n, b), src);
    }
}

template<typename Unsigned>
inline Unsigned position(size_t i) {
    return i < nBits<Unsigned>() ? shiftLeft(Unsigned(1), i) : Unsigned(0);
}

template<typename Unsigned>
inline Unsigned positionLsb(Unsigned src, size_t w, size_t i) {
    ASSERT_require(w <= nBits(src));
    return select(lowMask<Unsigned>(w), position<Unsigned>(i), src);
}

template<typename Unsigned>
inline Unsigned mask(size_t least, size_t greatest) {
    ASSERT_require(greatest < nBits<Unsigned>());
    ASSERT_require(greatest >= least);
    return shiftLeft(lowMask<Unsigned>(greatest - least + 1), least);
}

template<typename Unsigned>
inline Unsigned maskLsb(Unsigned src, size_t w, size_t least, size_t greatest) {
    ASSERT_require(w <= nBits(src));
    return select(lowMask<Unsigned>(w), mask<Unsigned>(least, greatest), src);
}

template<typename Unsigned>
inline bool bit(Unsigned src, size_t i) {
    return i < nBits(src) ? (src & position<Unsigned>(i)) != 0 : false;
}

template<typename Unsigned>
inline bool bitLsb(Unsigned src, size_t w, size_t i) {
    return i < w ? (src & position<Unsigned>(i)) != 0 : false;
}

template<typename Unsigned>
inline bool msb(Unsigned src) {
    return bit(src, nBits(src) - 1);
}

template<typename Unsigned>
inline bool msbLsb(Unsigned src, size_t w) {
    ASSERT_require(w <= nBits(src));
    return w > 0 ? bit(src, w-1) : false;
}

template<typename Unsigned>
inline Unsigned shiftRightSigned(Unsigned src, size_t n) {
    return shiftRight(src, n, msb(src));
}


template<typename Unsigned>
inline Unsigned shiftRightSigned(Unsigned src, size_t w, size_t n) {
    return shiftRightLsb(src, n, w, msbLsb(src, w));
}

template<typename Unsigned>
inline Unsigned bits(Unsigned src, size_t least, size_t greatest) {
    return shiftRight(src & mask<Unsigned>(least, greatest), least);
}

template<typename Unsigned>
inline Unsigned bitsLsb(Unsigned src, size_t w, size_t least, size_t greatest) {
    return shiftRight(src & mask<Unsigned>(least, greatest) & lowMask<Unsigned>(w), least);
}


template<typename UnsignedTarget, typename UnsignedSource>
inline UnsignedTarget convert(UnsignedSource x, bool b = false) {
    if (nBits(x) < nBits<UnsignedTarget>()) {
        // extending
        return UnsignedTarget(x) | (all<UnsignedTarget>(b) & ~lowMask<UnsignedTarget>(nBits(x)));
    } else {
        // truncating
        return UnsignedTarget(x & lowMask<UnsignedSource>(nBits<UnsignedTarget>()));
    }
}

template<typename UnsignedTarget, typename UnsignedSource>
inline UnsignedTarget convertSigned(UnsignedSource x) {
    return convert<UnsignedTarget>(x, msb(x));
}

template<typename Unsigned>
inline Unsigned signExtend(Unsigned src, size_t n) {
    if (n < nBits(src)) {
        if (msbLsb(src, n)) {
            src |= mask<Unsigned>(n, nBits(src)-1);
        } else {
            src &= ~mask<Unsigned>(n, nBits(src)-1);
        }
    }
    return src;
}

template<typename Unsigned>
inline Unsigned signExtendLsb(Unsigned src, size_t n, size_t m) {
    ASSERT_require(n > 0);
    ASSERT_require(m >= n);
    ASSERT_require(m <= nBits(src));
    if (m == n) {
        return src;
    } else {
        Unsigned newBitsMask = mask<Unsigned>(n, m-1);
        if (bit(src, n-1)) {
            return src | newBitsMask;
        } else {
            return src & ~newBitsMask;
        }
    }
}

template<typename Unsigned>
inline Unsigned rotateLeft(Unsigned src, size_t n) {
    n %= nBits(src);
    return shiftLeft(src, n) | shiftRight(src, nBits(src)-n);
}

template<typename Unsigned>
inline Unsigned rotateLeftLsb(Unsigned src, size_t w, size_t n) {
    ASSERT_require(w <= nBits(src));
    n = w ? n % w : 0;
    return select(lowMask<Unsigned>(w),
                  shiftLeftLsb(src, w, n) | shiftRightLsb(src, w-n),
                  src);
}

template<typename Unsigned>
inline Unsigned rotateRight(Unsigned src, size_t n) {
    n %= nBits(src);
    return shiftRight(src, n) | shiftLeft(src, nBits(src)-n);
}

template<typename Unsigned>
inline Unsigned rotateRightLsb(Unsigned src, size_t w, size_t n) {
    ASSERT_require(w <= nBits(src));
    n = w ? n % w : 0;
    return select(lowMask<Unsigned>(w),
                  shiftRightLsb(src, w, n) | shiftLeftLsb(src, w, w-n),
                  src);
}

template<typename Unsigned>
inline Unsigned replicate(Unsigned src, size_t n) {
    ASSERT_require(n != 0);
    if (n >= nBits(src)) {
        return src;
    } else {
        size_t ngroups = (nBits(src) + 1) / n;
        Unsigned retval = 0;
        for (size_t i = 0; i < ngroups; ++i)
            retval |= shiftLeft(src & lowMask<Unsigned>(n), i*n);
        return retval;
    }
}

template<typename Unsigned>
inline Unsigned replicateLsb(Unsigned src, size_t w, size_t n) {
    ASSERT_require(w <= nBits(src));
    return select(lowMask<Unsigned>(w), replicate(src, n), src);
}

template<typename Unsigned>
inline Sawyer::Optional<size_t> highestSetBit(Unsigned src) {
    if (src) {
        for (size_t i = nBits(src); i > 0; --i) {
            if (bit(src, i-1))
                return i-1;
        }
    }
    return Sawyer::Nothing();
}

template<typename Unsigned>
inline size_t nSet(Unsigned src) {
    size_t retval = 0;
    while (src != 0) {
        if ((src & 1) != 0)
            ++retval;
        src >>= 1;
    }
    return retval;
}

template<class T>
typename std::enable_if<std::is_integral<T>::value, T>::type
inline reverseBytes(const T &x) {
    // In C++23 and later, use std::byteswap
    using Unsigned = typename std::make_unsigned<T>::type;
    Unsigned u = x;
    const size_t n = sizeof(Unsigned);
    for (size_t i = 0; i < n/2; ++i) {
        const size_t loOffset = i*8;
        const size_t hiOffset = nBits<Unsigned>() - i*8 - 8;
        const auto loMask = mask<Unsigned>(loOffset, loOffset+7);
        const auto hiMask = mask<Unsigned>(hiOffset, hiOffset+7);
        const Unsigned lo = (u >> loOffset) & 0xff;
        const Unsigned hi = (u >> hiOffset) & 0xff;

        u &= ~(loMask | hiMask);
        u |= lo << hiOffset;
        u |= hi << loOffset;
    }
    return u;
}

inline bool
isBigEndian() {
    static const unsigned i = 1;
    return *(unsigned char*)&i == 0;
}

inline bool
isLittleEndian() {
    static const unsigned i = 1;
    return *(unsigned char*)&i == 1;
}

template<class T>
inline typename std::enable_if<std::is_integral<T>::value, T>::type
toBigEndian(const T x) {
    using U = typename std::make_unsigned<T>::type;
    return isBigEndian() ? x : reverseBytes((U)x);
}

template<class T>
inline typename std::enable_if<std::is_integral<T>::value, T>::type
toLittleEndian(const T x) {
    using U = typename std::make_unsigned<T>::type;
    return isLittleEndian() ? x : reverseBytes((U)x);
}

template<class T>
inline typename std::enable_if<std::is_integral<T>::value, T>::type
fromBigEndian(const T x) {
    using U = typename std::make_unsigned<T>::type;
    return isBigEndian() ? x : reverseBytes((U)x);
}

template<class T>
inline typename std::enable_if<std::is_integral<T>::value, T>::type
fromLittleEndian(const T x) {
    using U = typename std::make_unsigned<T>::type;
    return isLittleEndian() ? x : reverseBytes((U)x);
}

} // namespace
} // namespace
#endif