negative binary subtraction using 2's complement (and 5 bit representation)
I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;
8 in binary is 01000.
11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.
Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?
binary
asked Nov 5 '17 at 19:25
Alice S
11
add a comment |
I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;
8 in binary is 01000.
11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.
Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?
binary
asked Nov 5 '17 at 19:25
Alice S
11
add a comment |
I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;
8 in binary is 01000.
11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.
Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?
binary
asked Nov 5 '17 at 19:25
Alice S
11
I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;
8 in binary is 01000.
11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.
Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?
binary
binary
asked Nov 5 '17 at 19:25
Alice S
11
asked Nov 5 '17 at 19:25
Alice S
11
asked Nov 5 '17 at 19:25
Alice S
11
asked Nov 5 '17 at 19:25
Alice S
11
asked Nov 5 '17 at 19:25
Alice S
11
11
add a comment |
add a comment |
1 Answer
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You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$
8 = 01000
-11 = inv(01011)+1 = 10100+1 = 10101
01000
+ 10101
= 11101
Now compute $-3$ and see that results match:
-3 = inv(00011)+1 = 11100+1 = 11101
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
add a comment |
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1 Answer
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1 Answer
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active
oldest
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active
oldest
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active
oldest
votes
You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$
8 = 01000
-11 = inv(01011)+1 = 10100+1 = 10101
01000
+ 10101
= 11101
Now compute $-3$ and see that results match:
-3 = inv(00011)+1 = 11100+1 = 11101
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
add a comment |
You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$
8 = 01000
-11 = inv(01011)+1 = 10100+1 = 10101
01000
+ 10101
= 11101
Now compute $-3$ and see that results match:
-3 = inv(00011)+1 = 11100+1 = 11101
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
add a comment |
You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$
8 = 01000
-11 = inv(01011)+1 = 10100+1 = 10101
01000
+ 10101
= 11101
Now compute $-3$ and see that results match:
-3 = inv(00011)+1 = 11100+1 = 11101
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$
8 = 01000
-11 = inv(01011)+1 = 10100+1 = 10101
01000
+ 10101
= 11101
Now compute $-3$ and see that results match:
-3 = inv(00011)+1 = 11100+1 = 11101
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
edited Nov 5 '17 at 20:37
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
answered Nov 5 '17 at 20:31
gammatester
16.6k21632
16.6k21632
add a comment |
add a comment |
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