CODEWITHSUNDEEP
binaryhextwos-complement
Guy
Guy

Reputation: 1067

How to add hex numbers using two's complement?

I'm taking a beginner Computer Science course at my local college and one of the parts of this assignment asks me to convert a hex number to its hex equivalent. We use an online basic computer to do this that takes specific inputs specific inputs.

So according to my Appendix, when I type in a certain code it is supposed to "add the bit patterns [ED] and [09] as though they were two's complement representations." When I type the code into the system, it gives an output of F6... but I have no idea how it got there.

I understand how adding in two's complement works and I understand how to add two normal hex numbers, but when I add 09 (which is supposed to be the hex version of two's complement 9) and ED (which is supposed to be the hex version of two's complement -19), I get 10 if adding in two's complement or 162 if adding in hex.

Upvotes: 0

Views: 2133

Answers (1)

beaker
beaker

Reputation: 16791

Okay, you're just confusing yourself. Stop converting. This is all in hexadecimal:

  ED
+ 09
----

D + 9 = 16    // keep the 6 and carry the 1

  1
  ED
+ 09
----
   6

1 + E = F

  ED
+ 09
----
  F6

Regarding the first step, using 0x to denote hex numbers so we don't get lost:

0xD = 13,
0x9 = 9, 
13 + 9 = 22, 
22 = 0x16

therefore

0xD + 0x9 = 0x16

Gotta run, but just one more quick edit before I go.

D + 1 = E
D + 2 = F
D + 3 = 10  (remember, this is hex, so this is not "ten")
D + 4 = 11
...
D + 9 = 16

Upvotes: 1

Related Questions