Added support for fing buffer Swap(), Erase() and Flatten() functions

src/jc/cpp/ringbuffer.h

@@ -20,6 +20,15 @@
 #include <stdlib.h>
 #include <assert.h> // disable with NDEBUG
 
+#include <string.h> // memmove
+
+#define JC_SWAP(type, lhs, rhs)\
+    {\
+        type tmp = rhs;\
+        rhs = lhs;\
+        lhs = tmp;\
+    }
+
 namespace jc
 {
 
@@ -34,6 +43,14 @@ class RingBuffer
     RingBuffer(uint32_t capacity) : m_Buffer(0), m_Head(0), m_Tail(0), m_Max(0) { SetCapacity(capacity); }
     ~RingBuffer()                               { Free(); }
 
+    void Swap(RingBuffer<T>& rhs)               {
+                                                    JC_SWAP(T*,       m_Buffer, rhs.m_Buffer);
+                                                    JC_SWAP(uint32_t, m_Head,   rhs.m_Head);
+                                                    JC_SWAP(uint32_t, m_Tail,   rhs.m_Tail);
+                                                    JC_SWAP(uint32_t, m_Max,    rhs.m_Max);
+                                                    JC_SWAP(uint32_t, m_Full,   rhs.m_Full);
+                                                }
+
     /// Gets the size of the buffer
     uint32_t    Size() const                    {
                                                     if (m_Full)
@@ -51,20 +68,29 @@ class RingBuffer
     uint32_t    Capacity() const                { return (uint32_t)m_Max; }
     /// Increases or decreases capacity. Invalidates pointers to elements
     void        SetCapacity(uint32_t capacity);
+    /// Increases or decreases capacity. Invalidates pointers to elements
+    void        OffsetCapacity(uint32_t grow);
+
     /// Adds one item to the ring buffer. Asserts if the buffer is full
     void        Push(const T& item);
     /// Adds one item to the ring buffer. Does not assert, If full, overwrites the value at the tail.
     void        PushUnchecked(const T& item);
     /// Removes (and returns) the first inserted item from the ring buffer. Asserts if the buffer is empty
     T           Pop();
+    /// Removes the element at logical index (0-based) and keeps order
+    void        Erase(uint32_t index);
 
     T&          operator[] (size_t i)           { assert(i < Size()); return m_Buffer[(m_Tail + i) % m_Max]; }
     const T&    operator[] (size_t i) const     { assert(i < Size()); return m_Buffer[(m_Tail + i) % m_Max]; }
 
+    // Useful for sorting
+    void        Flatten();           // in-place linearization so data starts at m_Buffer[0]
+    void        FlattenUnordered();  // compacts contiguously without preserving logical order
+    T*          Buffer() const               { return m_Buffer; }
+
     // Mainly for unit tests
     uint32_t    Head() const                 { return m_Head; }
     uint32_t    Tail() const                 { return m_Tail; }
-    T*          Buffer() const               { return m_Buffer; }
 
 private:
     T*          m_Buffer;
@@ -78,6 +104,8 @@ class RingBuffer
     RingBuffer<T>& operator= (const RingBuffer<T>& rhs);
     bool operator== (const RingBuffer<T>& rhs);
 
+    void ReverseRange(uint32_t begin, uint32_t end_exclusive);
+
     void Free() {
         free(m_Buffer);
         m_Buffer = 0;
@@ -136,6 +164,12 @@ void RingBuffer<T>::SetCapacity(uint32_t capacity)
     m_Full = capacity == size ? 1 : 0;
 }
 
+template <typename T>
+void RingBuffer<T>::OffsetCapacity(uint32_t grow)
+{
+    SetCapacity(Capacity() + grow);
+}
+
 template <typename T>
 void RingBuffer<T>::Push(const T& item)
 {
@@ -160,13 +194,133 @@ T RingBuffer<T>::Pop()
     return item;
 }
 
+template <typename T>
+void RingBuffer<T>::Erase(uint32_t index)
+{
+    uint32_t size = Size();
+    assert(index < size);
+
+    // Compute physical index of the element to erase
+    uint32_t pos = (m_Tail + index) % m_Max;
+
+    // Shift elements left from pos towards head to preserve order
+    // Stop when the next index equals m_Head (the logical end)
+    while (true)
+    {
+        uint32_t next = pos + 1;
+        if (next >= m_Max) next = 0;
+        if (next == m_Head)
+            break;
+        m_Buffer[pos] = m_Buffer[next];
+        pos = next;
+    }
+
+    // One element removed: move head back by one and clear full flag
+    if (m_Head == 0)
+    {
+        m_Head = m_Max - 1;
+    }
+    else
+    {
+        --m_Head;
+    }
+    m_Full = 0;
+}
+
+
+// some cases: .=free, T=Tail, H=Head, *=used
+//  1) [T****H....]
+//  2) [...T***H..]
+//  3) [*H...T****]
+
+template <typename T>
+void RingBuffer<T>::FlattenUnordered()
+{
+    uint32_t capacity = m_Max;
+    uint32_t size = Size();
+    if (size == 0 || m_Tail == 0)
+        return; // already contiguous or empty
+
+    if (m_Tail < m_Head)
+    {
+        // Single contiguous block at offset; shift entire block to start
+        memmove(m_Buffer, m_Buffer + m_Tail, sizeof(T) * size);
+    }
+    else
+    {
+        // Wrapped case: move the rightmost part down directly after the left part.
+        // This compacts elements into [0..size-1] without preserving order.
+        uint32_t right_len = capacity - m_Tail; // [m_Tail .. m_Max)
+        memmove(m_Buffer + m_Head, m_Buffer + m_Tail, sizeof(T) * right_len);
+    }
+
+    m_Tail = 0;
+    m_Head = size;
+}
+
+// In-place linearization. After this call, the logical sequence is contiguous
+// at m_Buffer[0..Size()-1]. Does not allocate temporary buffers.
+template <typename T>
+void RingBuffer<T>::Flatten()
+{
+    uint32_t capacity = m_Max;
+    uint32_t size = Size();
+
+    // Early out when already contiguous (tail at 0) or empty
+    // No state changes in these cases.
+    if (size == 0 || m_Tail == 0)
+        return;
+
+    if (m_Tail < m_Head)
+    {
+        // Single contiguous block but offset; shift down to index 0
+        memmove(m_Buffer, m_Buffer + m_Tail, sizeof(T) * size);
+    }
+    else
+    {
+        // Wrapped case: rotate the whole buffer left by m_Tail positions.
+        // This makes the logical tail land at index 0. Elements outside
+        // [0..size-1] are unspecified and may contain moved free slots.
+        uint32_t n = capacity;
+        uint32_t k = m_Tail % n;
+        if (k)
+        {
+            ReverseRange(0, k);
+            ReverseRange(k, n);
+            ReverseRange(0, n);
+        }
+    }
+
+    m_Tail = 0;
+    m_Head = size;
+}
+
+template <typename T>
+void RingBuffer<T>::ReverseRange(uint32_t begin, uint32_t end_exclusive)
+{
+    while (begin < end_exclusive)
+    {
+        --end_exclusive;
+        if (begin >= end_exclusive)
+            break;
+        T tmp = m_Buffer[begin];
+        m_Buffer[begin] = m_Buffer[end_exclusive];
+        m_Buffer[end_exclusive] = tmp;
+        ++begin;
+    }
+}
+
+
 } // namespace
 
+#undef JC_SWAP
+
 /*
 
 VERSION:
 
-    1.0 Initial version
+    1.1 2025-10-08  Added Swap(), Erase() and Flatten*() functions
+    1.0             Initial version
 
 
 LICENSE: