Convert 0x1234 to 0x11223344

Question

How do I expand the hexadecimal number 0x1234 to 0x11223344 in a high-performance way?

unsigned int c = 0x1234, b;
b = (c & 0xff) << 4 | c & 0xf |          


        

Answer 1

Another way is:

DWORD OrVal(DWORD & nible_pos, DWORD input_val, DWORD temp_val, int shift)
{
    if (nible_pos==0)
        nible_pos = 0x0000000F;
    else
        nible_pos = nible_pos << 4;
    DWORD nible = input_val & nible_pos;
    temp_val |= (nible << shift);
    temp_val |= (nible << (shift + 4));
    return temp_val;
}

DWORD Converter2(DWORD input_val)
{
    DWORD nible_pos = 0x00000000;
    DWORD temp_val = 0x00000000;
    temp_val = OrVal(nible_pos, input_val, temp_val, 0);
    temp_val = OrVal(nible_pos, input_val, temp_val, 4);
    temp_val = OrVal(nible_pos, input_val, temp_val, 8);
    temp_val = OrVal(nible_pos, input_val, temp_val, 12);
    return temp_val;
}

DWORD val2 = Converter2(0x1234);

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An optimized version (3 times faster):

DWORD Converter3(DWORD input_val)
{
    DWORD nible_pos = 0;
    DWORD temp_val = 0;
    int shift = 0;
    DWORD bit_nible[4] = { 0x000F, 0x000F0, 0x0F00, 0xF000 };

    for ( ; shift < 16; shift+=4 )
    {
        if (nible_pos==0)
            nible_pos = 0x0000000F;
        else
            nible_pos = nible_pos << 4;
        DWORD nible = input_val & nible_pos;
        temp_val |= (nible << shift);
        temp_val |= (nible << (shift + 4));
    }

    return temp_val;
}