[boost] Boost.En­dian comments

Subject: [boost] Boost.En­dian comments
From: tymofey (tymofey_at_[hidden])
Date: 2011-09-05 14:56:29

This is not a full review, but rather a few comments on the implementation of reorder(x) functions.
What you are doing is casting pointers around and assigning individual bytes, which might not really effective:

inline void reorder(int64_t source, int64_t& target)
{
    const char* s (reinterpret_cast<const char*>(&source));
    char * t (reinterpret_cast<char*>(&target) + sizeof(target) - 1);
    *t = *s;
    *--t = *++s;
    *--t = *++s;
    *--t = *++s;
    *--t = *++s;
    *--t = *++s;
    *--t = *++s;
    *--t = *++s;
}

it does eight increments, eight decrements, one addition, one substraction and eight assignments.
maybe something like:

inline void reorder(int64_t source, int64_t& target)
{
    target = ((source << 0x38) & 0xFF00000000000000)
           | ((source << 0x28) & 0x00FF000000000000)
           | ((source << 0x18) & 0x0000FF0000000000)
           | ((source << 0x08) & 0x000000FF00000000)
           | ((source >> 0x08) & 0x00000000FF000000)
           | ((source >> 0x18) & 0x0000000000FF0000)
           | ((source >> 0x28) & 0x000000000000FF00)
           | ((source >> 0x38) & 0x00000000000000FF);
}

would be more efficient?