results

# master
StringSlice.slice left half:         100   20628.67 µs/op
StringSlice.slice right half:         50   33514.14 µs/op
StringSlice.slice almost all:         50   40865.84 µs/op
StringSlice.slice -1:                 50   63981.30 µs/op

# PR
StringSlice.slice -1:           10000000   0.60 µs/op
StringSlice.slice left half:         100   15272.15 µs/op
StringSlice.slice right half:         50   29207.42 µs/op
StringSlice.slice almost all:         50   30960.10 µs/op

# speedup
# This is the ratio of (PR execution time) / (master execution time)
StringSlice:slice -1:         0.0
StringSlice:slice left half:  0.76
StringSlice:slice almost all: 0.77
StringSlice:slice right half: 0.88

slice_10000.ex

Benchfella.start duration: 1.0, format: :machine, verbose: true

defmodule StringSlice do
  use Benchfella

  @str String.duplicate("hello world", 10000)
  @len String.length(@str)

  bench "slice left half" do
    String.slice(@str, 0, div(@len,2))
  end

  bench "slice right half" do
    String.slice(@str, div(@len,2), @len-1)
  end

  bench "slice almost all" do
    String.slice(@str, 1, @len-1)
  end

  bench "slice -1" do
    String.slice(@str, 1..-1)
  end
end