1 files changed, 175 insertions, 0 deletions
diff --git a/src/diff.hh b/src/diff.hh
new file mode 100644
index 00000000..aa482acf
--- /dev/null
+++ b/src/diff.hh
@@ -0,0 +1,175 @@
+#include "array_view.hh"
+#include "vector.hh"
+
+namespace Kakoune
+{
+
+template<typename T>
+struct MirroredArray : public ArrayView<T>
+{
+    MirroredArray(ArrayView<T> data, int size)
+        : ArrayView<T>(data), size(size)
+    {
+        kak_assert(2 * size + 1 <= data.size());
+    }
+
+    T& operator[](int n) { return ArrayView<T>::operator[](n + size); }
+    const T& operator[](int n) const { return ArrayView<T>::operator[](n + size); }
+private:
+    int size;
+};
+
+struct Snake{ int x, y, u, v; bool add; }; 
+
+template<typename Iterator>
+Snake find_end_snake_of_further_reaching_dpath(Iterator a, int N, Iterator b, int M,
+                                               const MirroredArray<int>& V,
+                                               const int D, const int k)
+{
+    int x; // our position along a
+
+    const bool add = k == -D or (k != D and V[k-1] < V[k+1]);
+
+    // if diagonal on the right goes further along x than diagonal on the left,
+    // then we take a vertical edge from it to this diagonal, hence x = V[k+1]
+    if (add)
+        x = V[k+1];
+    // else, we take an horizontal edge from our left diagonal,x = V[k-1]+1
+    else
+        x = V[k-1]+1;
+
+    int y = x - k; // we are by construction on diagonal k, so our position along
+                   // b (y) is x - k.
+
+    int u = x, v = y;
+    // follow end snake along diagonal k
+    while (u < N and v < M and a[u] == b[v])
+        ++u, ++v;
+
+    return { x, y, u, v, add };
+}
+
+struct SnakeLen : Snake
+{
+    SnakeLen(Snake s, int d) : Snake(s), d(d) {}
+    int d;
+};
+
+template<typename Iterator>
+SnakeLen find_middle_snake(Iterator a, int N, Iterator b, int M,
+                           ArrayView<int> data1, ArrayView<int> data2)
+{
+    const int delta = N - M;
+    MirroredArray<int> V1{data1, N + M};
+    MirroredArray<int> V2{data2, N + M};
+
+    std::reverse_iterator<Iterator> ra{a + N}, rb{b + M};
+
+    for (int D = 0; D <= (M + N + 1) / 2; ++D)
+    {
+        for (int k1 = -D; k1 <= D; k1 += 2)
+        {
+            auto p = find_end_snake_of_further_reaching_dpath(a, N, b, M, V1, D, k1);
+            V1[k1] = p.u;
+
+            const int k2 = -(k1 - delta);
+            if ((delta % 2 != 0) and -(D-1) <= k2 and k2 <= (D-1))
+            {
+                if (V1[k1] + V2[k2] >= N)
+                    return { p, 2 * D - 1 };// return last snake on forward path
+            }
+        }
+
+        for (int k2 = -D; k2 <= D; k2 += 2)
+        {
+            auto p = find_end_snake_of_further_reaching_dpath(ra, N, rb, M, V2, D, k2);
+            V2[k2] = p.u;
+
+            const int k1 = -(k2 - delta);
+            if ((delta % 2 == 0) and -D <= k1 and k1 <= D)
+            {
+                if (V1[k1] + V2[k2] >= N)
+                    return { { N - p.u, M - p.v, N - p.x , M - p.y } , 2 * D };// return last snake on reverse path
+            }
+        }
+    }
+
+    kak_assert(false);
+}
+
+template<typename Iterator>
+struct Diff
+{
+    bool add;
+    Iterator begin;
+    Iterator end;
+};
+
+template<typename Iterator>
+void find_diff_rec(Iterator a, size_t N, Iterator b, size_t M,
+                   ArrayView<int> data1, ArrayView<int> data2,
+                   Vector<Diff<Iterator>>& diffs)
+{
+    if (N > 0 and M > 0)
+    {
+        auto middle_snake = find_middle_snake(a, N, b, M, data1, data2);
+        if (middle_snake.d > 1)
+        {
+            find_diff_rec(a, middle_snake.x, b, middle_snake.y,
+                          data1, data2, diffs);
+
+            find_diff_rec(a + middle_snake.u, N - middle_snake.u,
+                          b + middle_snake.v, M - middle_snake.v,
+                          data1, data2, diffs);
+        }
+        else if (middle_snake.d == 1)
+        {
+            int diag = 0;
+            while (a[diag] == b[diag])
+                ++diag;
+
+            if (middle_snake.add)
+                diffs.push_back({true, b + middle_snake.y, b + middle_snake.y + 1});
+            else
+                diffs.push_back({false, a + middle_snake.x-1, a + middle_snake.x});
+        }
+    }
+    else if (M > 0)
+        diffs.push_back({true, b, b + M});
+    else if (N > 0)
+        diffs.push_back({false, a, a + N});
+}
+
+template<typename Iterator>
+void compact_diffs(Vector<Diff<Iterator>>& diffs)
+{
+    if (diffs.size() < 2)
+        return;
+
+    auto out_it = diffs.begin();
+    for (auto it = out_it + 1; it != diffs.end(); ++it)
+    {
+        if (it->add == out_it->add and it->begin == out_it->end)
+            out_it->end = it->end;
+        else if (++out_it != it)
+            *out_it = *it;
+    }
+}
+
+template<typename Iterator>
+Vector<Diff<Iterator>> find_diff(Iterator a, size_t N, Iterator b, size_t M)
+{
+    Vector<int> data(4 * (N+M));
+    Vector<Diff<Iterator>> diffs;
+    const size_t max_D_size = 2 * (N + M) + 1;
+    find_diff_rec(a, N, b, M,
+                  {data.data(), max_D_size},
+                  {data.data() + max_D_size, max_D_size},
+                  diffs);
+
+    // compact_diffs(diffs);
+
+    return diffs;
+}
+
+}