lib/core: Perfize `substring` in `FlatString`

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>

diff --git a/lib/core/text/flat.nit b/lib/core/text/flat.nit
index 6e1e610..a72af19 100644 (file)
--- a/lib/core/text/flat.nit
+++ b/lib/core/text/flat.nit
@@ -359,26 +359,51 @@ class FlatString
 
        redef fun fast_cstring do return _items.fast_cstring(_first_byte)
 
+       redef fun substring_from(from) do
+               if from >= self._length then return empty
+               if from <= 0 then return self
+               var c = char_to_byte_index(from)
+               var st = c - _first_byte
+               var fln = bytelen - st
+               return new FlatString.full(items, fln, c, _length - from)
+       end
+
        redef fun substring(from, count)
        do
                assert count >= 0
 
                if from < 0 then
                        count += from
-                       if count < 0 then count = 0
+                       if count < 0 then return ""
                        from = 0
                end
 
-               if (count + from) > length then count = length - from
+               var ln = _length
+               if (count + from) > ln then count = ln - from
                if count <= 0 then return ""
                var end_index = from + count - 1
+               return substring_impl(from, count, end_index)
+       end
+
+       private fun substring_impl(from, count, end_index: Int): String do
+               var cache = _position
+               var dfrom = (cache - from).abs
+               var dend = (end_index - from).abs
+
+               var bytefrom: Int
+               var byteto: Int
+               if dfrom < dend then
+                       bytefrom = char_to_byte_index(from)
+                       byteto = char_to_byte_index(end_index)
+               else
+                       byteto = char_to_byte_index(end_index)
+                       bytefrom = char_to_byte_index(from)
+               end
 
-               var bytefrom = char_to_byte_index(from)
-               var byteto = char_to_byte_index(end_index)
                var its = _items
                byteto += its.length_of_char_at(byteto) - 1
 
-               var s = new FlatString.full(its, byteto - bytefrom + 1, bytefrom, byteto, count)
+               var s = new FlatString.full(its, byteto - bytefrom + 1, bytefrom, count)
                return s
        end