Question

What does this: packed_data &= ~(0xff << 18); do?

Answer 1

The code 'packed_data &= ~(0xff << 18);' clears the bits at positions 18 to 25 in the variable packed_data by using bitwise operators to first create a binary number with zeros in the target positions and then performing a bitwise AND with packed_data.

Step-by-step explanation:

The line of code packed_data &= ~(0xff << 18) is performing a bitwise operation in the context of programming. This operation serves to clear a specific set of bits within an integer variable called packed_data. The operation works in the following way:

• The hexadecimal value 0xff represents the decimal value 255, which in binary is 11111111 (a series of eight 1s).
• The << operator is the bitwise left shift operator, shifting the 1s in 0xff eighteen positions to the left, padding the right side with zeros.
• The ~ operator is the bitwise NOT operator, which inverts all the bits of its operand, turning 1s into 0s and vice versa.
• The &= operator is the bitwise AND assignment operator. It takes the current value of packed_data, performs a bitwise AND with the operand on the right side of the &=, and assigns the result back to packed_data.

The effect of the operation is to clear the bits at positions 18 through 25 (since 0xff has 8 bits) of the packed_data variable, setting them to 0, without affecting other bits in packed_data.