Shift Right

Every clock pulse, the data will shifted one bit.

1. 1-bit shift right

2. 2-bit shift right

3. 3-bit shift right

4. 4-bit shift right

Behavior:

• Shifting 1000 right divides it by 2.

Shift Left

Read the D lines from the above in reverse

Behavior:

• Shifting 0001 right multiplies it by 2.

Rotate Right

1. 1-bit rotate right

2. 2-bit rotate right

3. 3-bit rotate right

4. 4-bit rotate right

Behavior:

• LIFO behavior of a stack.

Rotate Left

You get the drill, just use the same circuit but read different D inputs right-to-left.

Example: How-to Copy A to B?

• Use a shift right and rotate to slowly copy the contents of A into B. After 4 clock pulses the copy will be completed.

Examples: Commands

Suppose this 5-address instruction command does R1 <- R2 + R3:

One optimization is to have the next instruction address stored in its own register.

This is a 4-address instruction command that does R1 <- R2 + R3:

How about another reduction? This one will do R1 <- R1 + R2

If we use a default register like ACC (Accumulator), we can do two-address: ACC <- R1 + ACC

JVM does the extreme, using a stack to make a zero-address language.