From 69f6532b8dbcec0af8799a495fb8f161a2e6b02a Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Mon, 9 Aug 2021 14:06:32 +1000
Subject: [PATCH] [common] ringbuffer: allow reverse iteration

---
 client/src/overlay/graphs.c        |  2 +-
 common/include/common/ringbuffer.h |  2 +-
 common/src/ringbuffer.c            | 36 +++++++++++++++++++++++-------
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/client/src/overlay/graphs.c b/client/src/overlay/graphs.c
index 3df640e0..df6ead23 100644
--- a/client/src/overlay/graphs.c
+++ b/client/src/overlay/graphs.c
@@ -158,7 +158,7 @@ static int graphs_render(void * udata, bool interactive,
       continue;
 
     struct BufferMetrics metrics = {};
-    ringbuffer_forEach(graph->buffer, rbCalcMetrics, &metrics);
+    ringbuffer_forEach(graph->buffer, rbCalcMetrics, &metrics, false);
 
     if (metrics.sum > 0.0f)
     {
diff --git a/common/include/common/ringbuffer.h b/common/include/common/ringbuffer.h
index 6203d6ac..5d62b98e 100644
--- a/common/include/common/ringbuffer.h
+++ b/common/include/common/ringbuffer.h
@@ -42,4 +42,4 @@ void ringbuffer_setPreOverwriteFn(RingBuffer rb, RingBufferValueFn fn,
 
 typedef bool (*RingBufferIterator)(int index, void * value, void * udata);
 void ringbuffer_forEach(const RingBuffer rb, RingBufferIterator fn,
-    void * udata);
+    void * udata, bool reverse);
diff --git a/common/src/ringbuffer.c b/common/src/ringbuffer.c
index 4519167e..8a470ee2 100644
--- a/common/src/ringbuffer.c
+++ b/common/src/ringbuffer.c
@@ -106,16 +106,36 @@ void ringbuffer_setPreOverwriteFn(const RingBuffer rb, RingBufferValueFn fn,
   rb->preOverwriteUdata = udata;
 }
 
-void ringbuffer_forEach(const RingBuffer rb, RingBufferIterator fn, void * udata)
+void ringbuffer_forEach(const RingBuffer rb, RingBufferIterator fn, void * udata,
+    bool reverse)
 {
-  int index = rb->start;
-  for(int i = 0; i < rb->count; ++i)
+  if (reverse)
   {
-    void * value = rb->values + index * rb->valueSize;
-    if (++index == rb->length)
-      index = 0;
+    int index = rb->start + rb->count - 1;
+    if (index >= rb->length)
+      index -= rb->length;
 
-    if (!fn(i, value, udata))
-      break;
+    for(int i = 0; i < rb->count; ++i)
+    {
+      void * value = rb->values + index * rb->valueSize;
+      if (--index == -1)
+        index = rb->length - 1;
+
+      if (!fn(i, value, udata))
+        break;
+    }
+  }
+  else
+  {
+    int index = rb->start;
+    for(int i = 0; i < rb->count; ++i)
+    {
+      void * value = rb->values + index * rb->valueSize;
+      if (++index == rb->length)
+        index = 0;
+
+      if (!fn(i, value, udata))
+        break;
+    }
   }
 }