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#ifndef diff_hh_INCLUDED
#define diff_hh_INCLUDED
// Implementation of the linear space variant of the algorithm described in
// "An O(ND) Difference Algorithm and Its Variations"
// (http://xmailserver.org/diff2.pdf)
#include "array_view.hh"
#include "vector.hh"
#include <functional>
#include <iterator>
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());
(*this)[1] = 0;
}
[[gnu::always_inline]]
T& operator[](int n) { return ArrayView<T>::operator[](n + size); }
[[gnu::always_inline]]
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, typename Equal>
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, Equal eq)
{
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 eq(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, typename Equal>
SnakeLen find_middle_snake(Iterator a, int N, Iterator b, int M,
ArrayView<int> data1, ArrayView<int> data2,
Equal eq)
{
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, eq);
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, eq);
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, p.add } , 2 * D };// return last snake on reverse path
}
}
}
kak_assert(false);
return { {}, 0 };
}
struct Diff
{
enum { Keep, Add, Remove } mode;
int len;
int posB;
int posA;
};
inline void append_diff(Vector<Diff>& diffs, Diff diff)
{
if (not diffs.empty() and diffs.back().mode == diff.mode
and (diff.mode != Diff::Add or
diffs.back().posB + diffs.back().len == diff.posB))
diffs.back().len += diff.len;
else
diffs.push_back(diff);
}
template<typename Iterator, typename Equal>
void find_diff_rec(Iterator a, int offA, int lenA,
Iterator b, int offB, int lenB,
ArrayView<int> data1, ArrayView<int> data2,
Equal eq, Vector<Diff>& diffs)
{
if (lenA > 0 and lenB > 0)
{
auto middle_snake = find_middle_snake(a + offA, lenA, b + offB, lenB, data1, data2, eq);
kak_assert(middle_snake.u <= lenA and middle_snake.v <= lenB);
if (middle_snake.d > 1)
{
find_diff_rec(a, offA, middle_snake.x,
b, offB, middle_snake.y,
data1, data2, eq, diffs);
if (int len = middle_snake.u - middle_snake.x)
append_diff(diffs, {Diff::Keep, len, 0});
find_diff_rec(a, offA + middle_snake.u, lenA - middle_snake.u,
b, offB + middle_snake.v, lenB - middle_snake.v,
data1, data2, eq, diffs);
}
else
{
if (middle_snake.d == 1)
{
const int diag = middle_snake.x - (middle_snake.add ? 0 : 1);
if (diag != 0)
append_diff(diffs, {Diff::Keep, diag, 0});
if (middle_snake.add)
append_diff(diffs, {Diff::Add, 1, offB + diag});
else
append_diff(diffs, {Diff::Remove, 1, 0});
}
if (int len = middle_snake.u - middle_snake.x)
append_diff(diffs, {Diff::Keep, len, 0});
}
}
else if (lenB > 0)
append_diff(diffs, {Diff::Add, lenB, offB});
else if (lenA > 0)
append_diff(diffs, {Diff::Remove, lenA, 0});
}
template<typename Iterator, typename Equal = std::equal_to<typename std::iterator_traits<Iterator>::value_type>>
Vector<Diff> find_diff(Iterator a, int N, Iterator b, int M, Equal eq = Equal{})
{
const int max = 2 * (N + M) + 1;
Vector<int> data(2*max);
Vector<Diff> diffs;
find_diff_rec(a, 0, N, b, 0, M,
{data.data(), (size_t)max}, {data.data() + max, (size_t)max},
eq, diffs);
return diffs;
}
}
#endif // diff_hh_INCLUDED
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