From 5e127578f0c68ee9baa67d867d75c6a714bd1176 Mon Sep 17 00:00:00 2001
From: Rob Austein <sra@hactrn.net>
Date: Tue, 27 Sep 2016 12:55:42 -0400
Subject: Add hal_ks_index_replace().

---
 hal_internal.h | 10 ++++++++++
 ks_flash.c     |  7 +------
 ks_index.c     | 42 +++++++++++++++++++++++++++++++++---------
 3 files changed, 44 insertions(+), 15 deletions(-)

diff --git a/hal_internal.h b/hal_internal.h
index 2318748..ef0d763 100644
--- a/hal_internal.h
+++ b/hal_internal.h
@@ -645,6 +645,16 @@ extern hal_error_t hal_ks_index_delete(hal_ks_index_t *ksi,
                                        const hal_uuid_t * const name,
                                        unsigned *blockno);
 
+/*
+ * Replace a key block with a new one, return new block number.
+ * Name of block does not change.  This is an optimization of
+ * a delete immediately followed by an add for the same name.
+ */
+
+extern hal_error_t hal_ks_index_replace(hal_ks_index_t *ksi,
+                                        const hal_uuid_t * const name,
+                                        unsigned *blockno);
+
 /*
  * RPC lowest-level send and receive routines. These are blocking, and
  * transport-specific (sockets, USB).
diff --git a/ks_flash.c b/ks_flash.c
index c53347b..895f7df 100644
--- a/ks_flash.c
+++ b/ks_flash.c
@@ -1012,16 +1012,11 @@ static hal_error_t update_pin_block(const unsigned b1,
    * the all-zeros UUID).  Maybe later.
    */
 
-  if ((err = hal_ks_index_delete(&db.ksi, &pin_uuid, &b2)) != HAL_OK)
+  if ((err = hal_ks_index_replace(&db.ksi, &pin_uuid, &b2)) != HAL_OK)
     return err;
 
-  if (b2 != b1)
-    return HAL_ERROR_IMPOSSIBLE;
-
   block->pin = *new_data;
 
-  err = hal_ks_index_add(&db.ksi, &pin_uuid, &b2);
-
   if (err == HAL_OK)
     cache_mark_used(block, b2);
 
diff --git a/ks_index.c b/ks_index.c
index b35d5e0..476faf9 100644
--- a/ks_index.c
+++ b/ks_index.c
@@ -170,7 +170,7 @@ hal_error_t hal_ks_index_add(hal_ks_index_t *ksi,
 
   /*
    * Grab first block on free list, which makes room to slide the
-   * index down by one slot so we can insert the new block number.
+   * index up by one slot so we can insert the new block number.
    */
 
   const size_t len = (ksi->used - where) * sizeof(*ksi->index);
@@ -215,14 +215,38 @@ hal_error_t hal_ks_index_delete(hal_ks_index_t *ksi,
   return HAL_OK;
 }
 
-/*
- * Might want a hal_ks_index_replace(), which would be an efficiency
- * hack replacement (roughly 2x) for a delete followed by an add with
- * the same name.  Implementation would be to find the old existing
- * block, pull the first block off the free list, sliding the free
- * list down, drop the new block in instead of the old, put the old
- * block at the end of the free list, and return the new block.
- */
+hal_error_t hal_ks_index_replace(hal_ks_index_t *ksi,
+                                 const hal_uuid_t * const name,
+                                 unsigned *blockno)
+{
+  if (ksi == NULL || ksi->index == NULL || ksi->names == NULL ||
+      ksi->size == 0 || ksi->used > ksi->size || name == NULL)
+    return HAL_ERROR_BAD_ARGUMENTS;
+
+  if (ksi->used == ksi->size)
+    return HAL_ERROR_NO_KEY_SLOTS_AVAILABLE;
+
+  int where;
+
+  if (ksi->used == 0 || !ks_find(ksi, name, &where))
+    return HAL_ERROR_KEY_NOT_FOUND;
+
+  /*
+   * Grab first block from free list, slide free list down, put old
+   * block at end of free list and replace old block with new block.
+   */
+
+  const size_t len = (ksi->size - ksi->used - 1) * sizeof(*ksi->index);
+  const uint16_t b = ksi->index[ksi->used];
+  memmove(&ksi->index[ksi->used + 1], &ksi->index[ksi->used], len);
+  ksi->index[ksi->size - 1] = ksi->index[where];
+  ksi->index[where] = b;
+
+  if (blockno != NULL)
+    *blockno = b;
+
+  return HAL_OK;
+}
 
 /*
  * Local variables:
-- 
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