Revise Bit manipulation for Cambridge 9618 (4.3)

A bitwise shift moves every bit in a register (a storage location, like a byte) to the left or right by a specified number of positions. Bits that are shifted off one end are discarded, and the empty spaces at the other end are filled in according to specific rules. These operations are extremely fast for a processor to execute and provide a highly efficient way to perform multiplication and division by powers of two.

Logical shifts are the simplest type of shift. They treat the number as a simple sequence of bits, regardless of whether it represents a signed or unsigned number. When shifting, the empty positions are always filled with zeros.

When working with signed numbers stored in two's complement format, a logical shift right can produce incorrect results for negative numbers. For example, shifting a negative number right with LSR would introduce a 0 at the MSB, making the number positive. To solve this, we use an Arithmetic Shift Right (ASR). This shift preserves the sign of the number by copying the original sign bit into the vacant positions. Note that an Arithmetic Shift Left is identical in operation to a Logical Shift Left.

Masking is a technique used to access or modify specific bits within a larger binary value, like a byte. It works by combining the value with a special bit pattern, called a mask, using a bitwise logical operator. The three key operators are AND, OR, and XOR.