bench-parse-md-wiki-internal-links.cr

require "benchmark"

def f2(str)
  str.gsub(/\[\[([[:alnum:]\-\/]+)\]\]/, "[\\1](/pages/\\1)")
end

def f3(str)
  cursor = 0
  String.build do |b|
    while cursor < str.size
      if link_begin = str.index("[[", cursor)
        text_begin = link_begin + 2
        if link_end = str.index("]]", text_begin)
          text_end = link_end - 1
          text = str[text_begin..text_end]
          b << str[cursor..(link_begin - 1)]
          b << "[" << text << "](/pages/" << text << ")"
          cursor = link_end + 2
        else
          b << str[cursor..-1]
          cursor = str.size
        end
      else
        b << str[cursor..-1]
        cursor = str.size
      end
    end
  end
end

def f4(str)
  cursor = 0
  String.build do |b|
    while cursor < str.size
      if (link_begin = str.index('[', cursor)) && str[link_begin + 1] == '['
        text_begin = link_begin + 2
        if (link_end = str.index(']', text_begin)) && str[link_end + 1] == ']'
          text_end = link_end - 1
          text = str[text_begin..text_end]
          b << str[cursor..(link_begin - 1)]
          b << '[' << text << "](/pages/" << text << ')'
          cursor = link_end + 2
        else
          b << str[cursor..-1]
          cursor = str.size
        end
      else
        b << str[cursor..-1]
        cursor = str.size
      end
    end
  end
end

PART2 = "](/pages/"
COPY1 = Pointer(UInt8).malloc(2048)
COPY2 = Pointer(UInt8).malloc(2048)

def f5(str)
  cursor = 0
  String.build do |b|
    while cursor < str.size
      if (link_begin = str.index('[', cursor)) && str[link_begin + 1] == '['
        text_begin = link_begin + 2
        if (link_end = str.index(']', text_begin)) && str[link_end + 1] == ']'
          text_end = link_end - 1
          # text
          size = text_end - text_begin
          # raise "STOP: not enough buffer" if size > 2047
          ptr = (str.to_unsafe + text_begin)
          ptr.copy_to(COPY1, size + 1)
          text = String.new ptr, size + 1
          # before the link
          size = (link_begin - 1) - cursor
          # raise "STOP: not enough buffer" if size > 2047
          ptr = (str.to_unsafe + cursor)
          ptr.copy_to(COPY2, size + 1)
          before_link = String.new ptr, size + 1
          b << before_link
          b << '[' << text << "](/pages/" << text << ')'
          cursor = link_end + 2
        else
          b << str[cursor..-1]
          cursor = str.size
        end
      else
        b << str[cursor..-1]
        cursor = str.size
      end
    end
  end
end

STR = "this is a test with [[my-page]] and co"

Benchmark.ips do |x|
  x.report("f2") { f2 STR }
  x.report("f3") { f3 STR }
  x.report("f4") { f4 STR }
  x.report("f5") { f5 STR }
end

pp f2 STR
pp f3 STR
pp f4 STR
pp f5 STR

f2   1.12M (892.42ns) (± 6.85%)  2.45× slower
f3   1.84M (542.11ns) (± 6.38%)  1.49× slower
f4   2.64M (378.86ns) (± 9.43%)  1.04× slower
f5   2.74M (364.86ns) (± 8.81%)       fastest
f2(STR) # => "this is a test with [my-page](/pages/my-page) and co"
f3(STR) # => "this is a test with [my-page](/pages/my-page) and co"
f4(STR) # => "this is a test with [my-page](/pages/my-page) and co"
f5(STR) # => "this is a test with [my-page](/pages/my-page) and co"

I don't think I can manage to get more performances than f4. I could be cool to do not have to allocate new sub-strings