Correctly presize table when setting from varags

 - Change LuaTable.presize to allocate the exact size, rather than the
   next power of two. Unfortunately this does matter when searching for
   nil boundaries.

 - Presize tables when assigning from varargs. Again, while this should
   be invisible in theory, it does have an observable difference when
   getting the table length.

Fixes #85

src/main/java/org/squiddev/cobalt/LuaTable.java

@@ -116,7 +116,7 @@ public LuaTable checkTable() {
 	 */
 	public void presize(int nArray) {
 		if (nArray > array.length) {
-			resize(1 << log2(nArray), nodes.length, false);
+			resize(nArray, nodes.length, false);
 		}
 	}
 

src/main/java/org/squiddev/cobalt/function/LuaInterpreter.java

@@ -554,6 +554,8 @@ static Varargs execute(final LuaState state, DebugFrame di, LuaInterpretedFuncti
 						if (b == 0) {
 							b = di.top - a - 1;
 							int m = b - di.extras.count();
+							tbl.presize(offset + b);
+
 							int j = 1;
 							for (; j <= m; j++) tbl.rawset(offset + j, stack[a + j]);
 							for (; j <= b; j++) tbl.rawset(offset + j, di.extras.arg(j - m));

src/test/resources/spec/table_spec.lua

@@ -56,6 +56,31 @@ describe("Lua tables", function()
 			expect(#{ 1, 2, 3, nil, 5, nil, 7, 8, 9 }):eq(9)
 			expect(#{ 1, nil, [2] = 2, 3 }):eq(3)
 		end)
+
+		it("behaves identically to PUC Lua after resizing", function()
+			local n = 8
+
+			-- We grow the array part to be of length N.
+			local tbl = {}
+			for i = 1, n do tbl[i] = true end
+			expect(#tbl):eq(n)
+
+			-- Then clear out all but the last value. This does not shrink the array part, so we
+			-- still have a length N.
+			for i = 1, n - 1 do tbl[i] = nil end
+			expect(#tbl):eq(n)
+		end)
+	end)
+
+	describe("can be constructed from varargs", function()
+		it("presizes the array", function()
+			local function create(...) return { ... } end
+
+			-- If we'd constructed this table normally, it'd have a length of 5. However,
+			-- SETLIST will presize the table to ensure the array part is of length 5. As
+			-- the last slot is full, the array is considered saturated.
+			expect(#create(nil, nil, nil, nil, 1)):eq(5)
+		end)
 	end)
 
 	describe("weak tables", function()