[pypy-dev] OT: abs(x) with 4 assembly insns

[Damien Morton]

>From http://www.hackersdelight.org/basics.pdf

If your machine does not have an instruction for computing the absolute
value,
this computation can usually be done in three or four branch-free
instructions.
First, compute:

signed int x
signed int y = x >> 31

and then one of the following:
abs = (x ^ y) - y
abs = (x + y) ^ y
abs = x - ((x<<1) & y)