Fix example of ones' complement sum

[lvgrr]

book/direct/error.rst

Lines 108 to 118 in dd26bf8

	In ones’ complement arithmetic, a negative integer (-x) is represented
	as the complement of x; that is, each bit of x is inverted. When adding
	numbers in ones’ complement arithmetic, a carryout from the most
	significant bit needs to be added to the result. Consider, for example,
	the addition of -5 and -3 in ones’ complement arithmetic on 4-bit
	integers: +5 is 0101, so -5 is 1010; +3 is 0011, so -3 is 1100. If we
	add 1010 and 1100, ignoring the carry, we get 0110. In ones’ complement
	arithmetic, the fact that this operation caused a carry from the most
	significant bit causes us to increment the result, giving 0111, which is
	the ones’ complement representation of -8 (obtained by inverting the
	bits in 1000), as we would expect.

The example of ones' complement sum above is wrong because -8 cannot be represented in ones' complement arithmetic on 4-bit integers. 0111 is the representation of 7, not -8.

I propose changing the example to the sum -5 and -2.

[CLAassistant]

All committers have signed the CLA.

[drbruced12]

Agreed, the text as written is either confusing or wrong; this is a helpful fix.