Julia: High Performance Programming

Allocations and in-place operations

Consider the following trivial function, xpow, which takes an integer as input and returns the first few powers of the number. Another function, xpow_loop, uses the first function to compute the sum of squares of a large sequence of numbers, as follows:

function xpow(x)
   return [x x^2 x^3 x^4]
end

function xpow_loop(n)
    s = 0
    for i = 1:n
      s = s + xpow(i)[2]
    end
   return s
end

Benchmarking this function for a large input shows that this function is quite slow, as follows:

julia> @benchmark xpow_loop(1000000)
================ Benchmark Results ========================
     Time per evaluation: 103.17 ms [101.39 ms, 104.95 ms]
Proportion of time in GC: 13.15% [12.76%, 13.53%]
        Memory allocated: 152.58 mb
 Number of allocations: ...