bitmask.hpp

#ifndef _C4_BITMASK_HPP_
#define _C4_BITMASK_HPP_

/** @file bitmask.hpp bitmask utilities */

#include <cstring>
#include <type_traits>

#include "c4/enum.hpp"
#include "c4/format.hpp"

#if defined(_MSC_VER)
#   pragma warning(push)
#   pragma warning(disable : 4996) // 'strncpy', fopen, etc: This function or variable may be unsafe
#endif

#if defined(__clang__)
#   pragma clang diagnostic push
#   pragma clang diagnostic ignored "-Wold-style-cast"
#elif defined(__GNUC__)
#   pragma GCC diagnostic push
#   pragma GCC diagnostic ignored "-Wold-style-cast"
#   if __GNUC__ >= 8
#       pragma GCC diagnostic ignored "-Wstringop-truncation"
#       pragma GCC diagnostic ignored "-Wstringop-overflow"
#   endif
#endif

namespace c4 {

//-----------------------------------------------------------------------------
/** write a bitmask to a stream, formatted as a string */

template<class Enum, class Stream>
Stream& bm2stream(Stream &s, typename std::underlying_type<Enum>::type bits, EnumOffsetType offst=EOFFS_PFX)
{
    using I = typename std::underlying_type<Enum>::type;
    bool written = false;

    auto const& pairs = esyms<Enum>();

    // write non null value
    if(bits)
    {
        // do reverse iteration to give preference to composite enum symbols,
        // which are likely to appear at the end of the enum sequence
        for(size_t i = pairs.size() - 1; i != size_t(-1); --i)
        {
            auto p = pairs[i];
            I b(static_cast<I>(p.value));
            if(b && (bits & b) == b)
            {
                if(written) s << '|'; // append bit-or character
                written = true;
                s << p.name_offs(offst); // append bit string
                bits &= ~b;
            }
        }
        return s;
    }
    else
    {
        // write a null value
        for(size_t i = pairs.size() - 1; i != size_t(-1); --i)
        {
            auto p = pairs[i];
            I b(static_cast<I>(p.value));
            if(b == 0)
            {
                s << p.name_offs(offst);
                written = true;
                break;
            }
        }
    }
    if(!written)
    {
        s << '0';
    }
    return s;
}

template<class Enum, class Stream>
typename std::enable_if<is_scoped_enum<Enum>::value, Stream&>::type
bm2stream(Stream &s, Enum value, EnumOffsetType offst=EOFFS_PFX)
{
    using I = typename std::underlying_type<Enum>::type;
    return bm2stream<Enum>(s, static_cast<I>(value), offst);
}


//-----------------------------------------------------------------------------

// some utility macros, undefed below

/// @cond dev

/* Execute `code` if the `num` of characters is available in the str
 * buffer. This macro simplifies the code for bm2str().
 * @todo improve performance by writing from the end and moving only once. */
#define _c4prependchars(code, num)                                      \
    if(str && (pos + num <= sz))                                        \
    {                                                                   \
        /* move the current string to the right */                      \
        memmove(str + num, str, pos);                                   \
        /* now write in the beginning of the string */                  \
        code;                                                           \
    }                                                                   \
    else if(str && sz)                                                  \
    {                                                                   \
        C4_ERROR("cannot write to string pos=%d num=%d sz=%d",          \
                 (int)pos, (int)num, (int)sz);                          \
    }                                                                   \
    pos += num

/* Execute `code` if the `num` of characters is available in the str
 * buffer. This macro simplifies the code for bm2str(). */
#define _c4appendchars(code, num)                                       \
    if(str && (pos + num <= sz))                                        \
    {                                                                   \
        code;                                                           \
    }                                                                   \
    else if(str && sz)                                                  \
    {                                                                   \
        C4_ERROR("cannot write to string pos=%d num=%d sz=%d",          \
                 (int)pos, (int)num, (int)sz);                          \
    }                                                                   \
    pos += num

/// @endcond


/** convert a bitmask to string.
 * return the number of characters written. To find the needed size,
 * call first with str=nullptr and sz=0 */
template<class Enum>
size_t bm2str
(
    typename std::underlying_type<Enum>::type bits,
    char *str=nullptr,
    size_t sz=0,
    EnumOffsetType offst=EOFFS_PFX
)
{
    using I = typename std::underlying_type<Enum>::type;
    C4_ASSERT((str == nullptr) == (sz == 0));

    auto syms = esyms<Enum>();
    size_t pos = 0;
    typename EnumSymbols<Enum>::Sym const* C4_RESTRICT zero = nullptr;

    // do reverse iteration to give preference to composite enum symbols,
    // which are likely to appear later in the enum sequence
    for(size_t i = syms.size()-1; i != size_t(-1); --i)
    {
        auto const &C4_RESTRICT p = syms[i]; // do not copy, we are assigning to `zero`
        I b = static_cast<I>(p.value);
        if(b == 0)
        {
            zero = &p; // save this symbol for later
        }
        else if((bits & b) == b)
        {
            bits &= ~b;
            // append bit-or character
            if(pos > 0)
            {
                _c4prependchars(*str = '|', 1);
            }
            // append bit string
            const char *pname = p.name_offs(offst);
            size_t len = strlen(pname);
            _c4prependchars(strncpy(str, pname, len), len);
        }
    }

    C4_CHECK_MSG(bits == 0, "could not find all bits");
    if(pos == 0) // make sure at least something is written
    {
        if(zero) // if we have a zero symbol, use that
        {
            const char *pname = zero->name_offs(offst);
            size_t len = strlen(pname);
            _c4prependchars(strncpy(str, pname, len), len);
        }
        else // otherwise just write an integer zero
        {
            _c4prependchars(*str = '0', 1);
        }
    }
    _c4appendchars(str[pos] = '\0', 1);

    return pos;
}


// cleanup!
#undef _c4appendchars
#undef _c4prependchars


/** scoped enums do not convert automatically to their underlying type,
 * so this SFINAE overload will accept scoped enum symbols and cast them
 * to the underlying type */
template<class Enum>
typename std::enable_if<is_scoped_enum<Enum>::value, size_t>::type
bm2str
(
    Enum bits,
    char *str=nullptr,
    size_t sz=0,
    EnumOffsetType offst=EOFFS_PFX
)
{
    using I = typename std::underlying_type<Enum>::type;
    return bm2str<Enum>(static_cast<I>(bits), str, sz, offst);
}


//-----------------------------------------------------------------------------

namespace detail {

#ifdef __clang__
#   pragma clang diagnostic push
#elif defined(__GNUC__)
#   pragma GCC diagnostic push
#   if __GNUC__ >= 6
#       pragma GCC diagnostic ignored "-Wnull-dereference"
#   endif
#endif

template<class Enum>
typename std::underlying_type<Enum>::type str2bm_read_one(const char *str, size_t sz, bool alnum)
{
    using I = typename std::underlying_type<Enum>::type;
    auto pairs = esyms<Enum>();
    if(alnum)
    {
        auto *p = pairs.find(str, sz);
        C4_CHECK_MSG(p != nullptr, "no valid enum pair name for '%.*s'", (int)sz, str);
        return static_cast<I>(p->value);
    }
    I tmp{0};
    size_t len = uncat(csubstr(str, sz), tmp);
    C4_CHECK_MSG(len != csubstr::npos, "could not read string as an integral type: '%.*s'", (int)sz, str);
    return tmp;
}

#ifdef __clang__
#   pragma clang diagnostic pop
#elif defined(__GNUC__)
#   pragma GCC diagnostic pop
#endif
} // namespace detail

/** convert a string to a bitmask */
template<class Enum>
typename std::underlying_type<Enum>::type str2bm(const char *str, size_t sz)
{
    using I = typename std::underlying_type<Enum>::type;

    I val = 0;
    bool started = false;
    bool alnum = false, num = false;
    const char *f = nullptr, *pc = str;
    for( ; pc < str+sz; ++pc)
    {
        const char c = *pc;
        if((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_')
        {
            C4_CHECK(( ! num) || ((pc - f) == 1 && (c == 'x' || c == 'X'))); // accept hexadecimal numbers
            if( ! started)
            {
                f = pc;
                alnum = started = true;
            }
        }
        else if(c >= '0' && c <= '9')
        {
            C4_CHECK( ! alnum);
            if(!started)
            {
                f = pc;
                num = started = true;
            }
        }
        else if(c == ':' || c == ' ')
        {
            // skip this char
        }
        else if(c == '|' || c == '\0')
        {
            C4_ASSERT(num != alnum);
            C4_ASSERT(pc >= f);
            val |= detail::str2bm_read_one<Enum>(f, static_cast<size_t>(pc-f), alnum);
            started = num = alnum = false;
            if(c == '\0')
            {
                return val;
            }
        }
        else
        {
            C4_ERROR("bad character '%c' in bitmask string", c);
        }
    }

    if(f)
    {
        C4_ASSERT(num != alnum);
        C4_ASSERT(pc >= f);
        val |= detail::str2bm_read_one<Enum>(f, static_cast<size_t>(pc-f), alnum);
    }

    return val;
}

/** convert a string to a bitmask */
template<class Enum>
typename std::underlying_type<Enum>::type str2bm(const char *str)
{
    return str2bm<Enum>(str, strlen(str));
}

} // namespace c4

#ifdef _MSC_VER
#   pragma warning(pop)
#endif

#if defined(__clang__)
#   pragma clang diagnostic pop
#elif defined(__GNUC__)
#   pragma GCC diagnostic pop
#endif

#endif // _C4_BITMASK_HPP_