fix shift_idx (#97)

Author: lgarithm

include/ttl/bits/std_shape.hpp

@@ -17,10 +17,10 @@ N product(Iterator begin, Iterator end)
 };
 
 template <size_t off, typename T, size_t r, size_t... Is>
-constexpr std::array<T, r - 1> shift_idx(const std::array<T, r> &a,
-                                         std::index_sequence<Is...>)
+constexpr std::array<T, r - off> shift_idx(const std::array<T, r> &a,
+                                           std::index_sequence<Is...>)
 {
-    return std::array<T, r - 1>({std::get<Is + off>(a)...});
+    return std::array<T, r - off>({std::get<Is + off>(a)...});
 }
 
 using rank_t = uint8_t;

tests/test_shape.cpp

@@ -181,7 +181,7 @@ TEST(shape_test, test_flatten)
     ASSERT_EQ(s8, ttl::shape<1>(720));
 }
 
-struct S {
+struct Test_constexpr {
     static constexpr auto shape = ttl::make_shape(2, 3);
 };
 
@@ -195,3 +195,12 @@ TEST(shape_test, test_batch_vectorize)
     auto vs1 = ttl::vectorize(shape);
     ASSERT_EQ(vs1, ttl::make_shape(2, 3, 1));
 }
+
+TEST(shape_test, test_subshape)
+{
+    auto s = ttl::make_shape(1, 2, 3, 4);
+    auto t1 = s.subshape();  // (2, 3, 4)
+    ASSERT_EQ(t1.size(), 24);
+    auto t2 = s.subshape<2>();  // (3, 4)
+    ASSERT_EQ(t2.size(), 12);
+}