tool/strip-rdoc.rb: optimize

This script is called from Doxygen many times.  Worth optimising.
[ci skip]

tool/strip-rdoc.rb

@@ -1,26 +1,14 @@
 #!ruby
+# frozen_string_literal: true
 
 # Filter for preventing Doxygen from processing RDoc comments.
 # Used by the Doxygen template.
 
-ARGF.binmode
-source = ARGF.read
-source = source.gsub(%r{/\*([!*])((?!\*/).+?)\*/}m) do |comment|
-  marker, comment = $1, $2
-  next "/**#{comment}*/" unless /^\s*\*\s?\-\-\s*$/ =~ comment
-  doxybody = nil
-  comment.each_line do |line|
-    if doxybody
-      if /^\s*\*\s?\+\+\s*$/ =~ line
-        break
-      end
-      doxybody << line
-    else
-      if /^\s*\*\s?--\s*$/ =~ line
-        doxybody = "\n"
-      end
-    end
-  end
-  "/*#{marker}#{doxybody}*/"
-end
-print source
+print ARGF.binmode.read.tap {|src|
+  src.gsub!(%r|(/\*[!*])(?:(?!\*/).)+?^\s*\*\s?\-\-\s*$(.+?\*/)|m) {
+    marker = $1
+    comment = $2
+    comment.sub!(%r|^\s*\*\s?\+\+\s*$.+?(\s*\*/)\z|m, '\\1')
+    marker + comment
+  }
+}