Fix RingBuffer::getReadableDataSize, add a few methods

Signed-off-by: falkTX <falktx@falktx.com>

distrho/extra/RingBuffer.hpp

@@ -200,14 +200,22 @@ class RingBufferControl
         return (buffer->buf == nullptr || buffer->head == buffer->tail);
     }
 
+    /*
+     * Get the full ringbuffer size.
+     */
+    uint32_t getSize() const noexcept
+    {
+        return buffer != nullptr ? buffer->size : 0;
+    }
+
     /*
      * Get the size of the data available to read.
      */
     uint32_t getReadableDataSize() const noexcept
     {
         DISTRHO_SAFE_ASSERT_RETURN(buffer != nullptr, 0);
 
-        const uint32_t wrap = buffer->head > buffer->tail ? 0 : buffer->size;
+        const uint32_t wrap = buffer->head >= buffer->tail ? 0 : buffer->size;
 
         return wrap + buffer->head - buffer->tail;
     }
@@ -219,7 +227,7 @@ class RingBufferControl
     {
         DISTRHO_SAFE_ASSERT_RETURN(buffer != nullptr, 0);
 
-        const uint32_t wrap = (buffer->tail > buffer->wrtn) ? 0 : buffer->size;
+        const uint32_t wrap = buffer->tail > buffer->wrtn ? 0 : buffer->size;
 
         return wrap + buffer->tail - buffer->wrtn;
     }
@@ -243,6 +251,20 @@ class RingBufferControl
         std::memset(buffer->buf, 0, buffer->size);
     }
 
+    /*
+     * Reset the ring buffer read and write positions, marking the buffer as empty.
+     * Requires a buffer struct tied to this class.
+     */
+    void flush() noexcept
+    {
+        DISTRHO_SAFE_ASSERT_RETURN(buffer != nullptr,);
+
+        buffer->head = buffer->tail = buffer->wrtn = 0;
+        buffer->invalidateCommit = false;
+
+        errorWriting = false;
+    }
+
     // -------------------------------------------------------------------
     // read operations