IEEE754 uses sign-magnitude, not 1's-complement. It doesn't use any sort of complementation.
Edit: Also, it looks like posits also use sign-magnitude and not 2's-complement? I am confused as to where you are getting this from. [Edit again: I was wrong about this, see below.]
Yes, sign-magnitude is the right terminology, my mistake, but too late to edit. As for two's complement, look at slide 18-19 from the link somebody produced below:
Hm, they do indeed use 2's-complement... sort of. In case of a negative posit, they don't apply 2's-complement to the mantissa or anything like that, but rather to the entire posit without regard to the meaning of the bits. That's... kind of surprising, huh! Although it's not the first number format to do that. But it is a sort of 2's-complement, yes...
Edit: Also, it looks like posits also use sign-magnitude and not 2's-complement? I am confused as to where you are getting this from. [Edit again: I was wrong about this, see below.]