From aca3db2b0661724d1acf94c9ee6b7a85bec826a0 Mon Sep 17 00:00:00 2001
From: "Justin R. Cutler" <justin.r.cutler@gmail.com>
Date: Sat, 9 Apr 2016 11:39:19 -0400
Subject: [PATCH] Add heap_replace() functionality

---
 src/heap.c        | 21 +++++++++++++++++++++
 test/heap.c       | 14 ++++++++++++--
 threadless/heap.h |  9 +++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/heap.c b/src/heap.c
index 9413bd6..a0d9758 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -84,6 +84,27 @@ int heap_push(heap_t *heap, heap_node_t *node)
 }
 
 
+void heap_replace(heap_node_t *old, heap_node_t *node)
+{
+    heap_t *heap = old->heap;
+    size_t pos = old->index;
+    heap_node_t **storage = heap->allocation.memory;
+
+    /* disassociate old node from heap */
+    old->heap = NULL;
+    old->index = 0;
+
+    /* place new node in heap */
+    node->heap = heap;
+    node->index = pos;
+    storage[pos] = node;
+
+    /* restore heap invariant */
+    sift_up(heap, pos, heap->count);
+    sift_down(heap, 0, pos);
+}
+
+
 void heap_remove(heap_node_t *node)
 {
     heap_t *heap = node->heap;
diff --git a/test/heap.c b/test/heap.c
index 991c783..c8023cd 100644
--- a/test/heap.c
+++ b/test/heap.c
@@ -30,7 +30,12 @@
 #include <threadless/heap.h>
 
 
-const int data[] = { 4 /* duplicate */, 1, 9, 2, 8, 4, 0, 5, 3, 6, 7, 99 };
+const int data[] = {
+    4 /* duplicate (remove) */,
+    6 /* duplicate (replace with 1) */,
+    9, 2, 8, 4, 0, 5, 3, 6, 7,
+    99 /* remove */,
+};
 const size_t data_count = sizeof(data) / sizeof(data[0]);
 
 
@@ -58,7 +63,7 @@ static int run(allocator_t *allocator)
     heap_node_t *node;
 
     allocation_init(&alloc, allocator);
-    error = allocation_realloc_array(&alloc, data_count, sizeof(*values));
+    error = allocation_realloc_array(&alloc, data_count + 1, sizeof(*values));
     if (error) {
         return error;
     }
@@ -74,9 +79,14 @@ static int run(allocator_t *allocator)
 
     /* remove from middle */
     heap_remove(&(values[0].node));
+
     /* remove from end */
     heap_remove(&(values[data_count - 1].node));
 
+    /* replace */
+    values[data_count].value = 1;
+    heap_replace(&(values[1].node), &(values[data_count].node));
+
     /* pull values out of heap (minimum first) */
     while (NULL != (node = heap_pop(&heap))) {
         value_t *value = container_of(node, value_t, node);
diff --git a/threadless/heap.h b/threadless/heap.h
index ed0369a..a52ffb7 100644
--- a/threadless/heap.h
+++ b/threadless/heap.h
@@ -84,6 +84,15 @@ static inline heap_node_t *heap_peek(const heap_t *heap)
  */
 int heap_push(heap_t *heap, heap_node_t *node);
 
+/** Replace an existing @p old node in a heap with a new @p node
+ * @param[in,out] old  old node
+ * @param[in,out] node new node
+ * @pre @p old must be in a heap
+ * @post @p old is no longer in a heap
+ * @post @p node is in the heap that previously contained @p old
+ */
+void heap_replace(heap_node_t *old, heap_node_t *node);
+
 /** Remove an arbitrary @p node from its heap
  * @param[in,out] node node
  * @pre @p node must be in a heap