Octal shorthand and 7's complement
The use of the phrase '1's complement fixed-point integer arithmetic operations' simply means there can be negative numbers, and how they are representative.
See paragraph for ones' complement system on http://en.wikipedia.org/wiki/1%27s_complement

In that situation 1's complement is an adjective, describing the numbering system.

That is not to be confused with the command (verb) to take (find, calculate, etc.) the complement.