Tue, 10 Sep 2013, 01:01

One more thing, I told you that the negative numbers were specified by choosing bit patterns such that when I add +A to -A, I will get 0. That is true! BUT, there is a useful shortcut, and my TAs ganged up on me and told me I better show it to you. So, here goes: Take the 6 bit positive number 011101. It is +29. What is the representation for -29. What would happen if I add to 011101 the representation with all bits flipped. That is 100010. 011101 100010 - 111111 What if I add to this 000001? 111111 000001 - 000000 I started with +29, which is 011101. I added the value obtained by "flipping all the bits" and then added 1 to it. My result is 0. Therefore, -29 must be "all bits flipped" +1. That is, 100010 000001 - 100011 Try it: 011101 +29 100011 - 000000 So, -29 is 100011. The negative of this must be +29. Flip all the bits and add 1. 011100 000001 - 011101 And I am back to -(-29) = +29. OK? See you on Wednesday. Yale Patt