Which is the fastest way to get the absolute value of a number

Question

Which is the fastest way to implement an operation that returns the absolute value of a number?

x=root(x²)

or

if !isPositiv         


        

Answer 1

For a list of negative numbers:

if you have zero stored in memory, simply use 0 - x, where x is the negative number.

Or if you do not have zero stored in memory:

x-x-x, where x is the negative number.

Or, with brackets for clarity:

(x) - (x) - (x) => (-n) - (-n) - (-n), where x = -n

i.e. subtract the negative number from itself to get zero, then subtract it from zero.