bit manipulation: clearing range of bits

Question

I\'m preparing for an interview using the text, \"Cracking the Coding Interview\" by Gayle Laakman McDowell. On the section covering bit manipulation, there are two function

Answer 1

// To clear all bits from the most significant bit through i (inclusive), we do:

int clearMSBthroughI(int num, int i) {
    int mask = (1 << i) - 1;
    return num & mask;
}

Take the example of i = 3
1<<3 gives you 0x00001000 
(1<<3)-1 gives you 0x00000111
num & (1<

// To clear all bits from i through 0 (inclusive), we do:

int clearBitsIthrough0(int num, int i) {
    int mask = ~(((1 << (i+1)) - 1);
    return num & mask;
}

same example of i = 3 gives you

1 <<(3+1) =0x00010000
1 <<(3+1)-1 = 0x00001111
mask =~(1<<(3+1)-1) = 0x11110000
num & mask will cleaR the bits from 0 throuh i