13. Clear Specific Bits in a 32-bit Register

You are given a 32-bit control register. Clear a group of bits (set them to 0) starting at a given position and length.

Other bits must stay untouched.

Example 1

Input: reg = 0b1111 1111, pos = 4, len = 4 
Output: 0b0000 1111

Example 2 

Input: reg = 0b0000 1111, pos = 0, len = 2 
Output: 0b0000 1100