a = d 4j+0 & 0x3;

This line of code is performing a bitwise operation on the variable d.

The ">>" symbol is the right shift operator, which shifts the binary representation of d to the right by (4*j+0) positions.

The "&" symbol is the bitwise AND operator, which compares the resulting binary value with the binary value of 0x3 (which is equivalent to binary 11).

The resulting value is assigned to the variable a.

Overall, this line of code is extracting a specific set of two bits from the binary representation of d, based on the value of j