Check value of least significant bit (LSB) and most significant bit (MSB) in C/C++

Question

I need to check the value of the least significant bit (LSB) and most significant bit (MSB) of an integer in C/C++. How would I do this?

Answer 1

LSB is easy. Just x & 1.

MSSB is a bit trickier, as bytes may not be 8 bits and sizeof(int) may not be 4, and there might be padding bits to the right.

Also, with a signed integer, do you mean the sign bit of the MS value bit.

If you mean the sign bit, life is easy. It's just x < 0

If you mean the most significant value bit, to be completely portable.

 int answer  = 0;
 int rack = 1;
 int mask  = 1;

 while(rack < INT_MAX)
 {
    rack << = 1;
    mask << = 1;
    rack |= 1; 
 } 

 return x & mask;

That's a long-winded way of doing it. In reality

x & (1 << (sizeof(int) * CHAR_BIT) - 2); will be quite portable enough and your ints won't have padding bits.