lib/string: faster substring for FlatBuffer

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/string.nit b/lib/standard/string.nit
index 0b4b1e9..d3aa602 100644 (file)
--- a/lib/standard/string.nit
+++ b/lib/standard/string.nit
@@ -1614,6 +1614,20 @@ class FlatBuffer
        # Create a new empty string.
        init do end
 
+       # Low-level creation a new buffer with given data.
+       #
+       # `items` will be used as is, without copy, to store the characters of the buffer.
+       # Aliasing issues is the responsibility of the caller.
+       #
+       # If `items` is shared, `written` should be set to true after the creation
+       # so that a modification will do a copy-on-write.
+       private init with_infos(items: NativeString, capacity, length: Int)
+       do
+               self.items = items
+               self.length = length
+               self.capacity = capacity
+       end
+
        # Create a new string copied from `s`.
        init from(s: Text)
        do
@@ -1638,7 +1652,6 @@ class FlatBuffer
        init with_capacity(cap: Int)
        do
                assert cap >= 0
-               # _items = new NativeString.calloc(cap)
                items = new NativeString(cap+1)
                capacity = cap
                length = 0
@@ -1682,11 +1695,10 @@ class FlatBuffer
                if from < 0 then from = 0
                if count > length then count = length
                if from < count then
-                       var r = new FlatBuffer.with_capacity(count - from)
-                       while from < count do
-                               r.chars.push(items[from])
-                               from += 1
-                       end
+                       var len = count - from
+                       var r_items = new NativeString(len)
+                       items.copy_to(r_items, len, from, 0)
+                       var r = new FlatBuffer.with_infos(r_items, len, len)
                        return r
                else
                        return new FlatBuffer