Question

I’m implementing a 16-bit bit shifter to rotate bits to the left by r. I only have access to the AND, NOT and ADD operations. There are 3 condition codes: negative, zero and positive, which are set when you use any of these operations.

This is my approach:

1. AND the number with 1000 0000 0000 0000 to set condition codes to positive if the most significant bit is 1.
2. ADD the number with itself. This shifts bits to the left by one.
3. If the MSB was 1, ADD 1 to the result.
4. Loop through steps (1)-(3) r times.

Are there any other efficient ways I can do this?

Answer 1

Since this is homework, I’ll help you think about it.

2 * 2 = 4
4 * 2 = 8
8 * 2 = 16

0010 * 0010 = 00100
0100 * 0010 = 01000
1000 * 0010 = 10000

A left shift is a [some unknown] operation. That [some unknown] operation can be implemented using AND, NOT and ADD by doing…