trie: cache fill_value value instead of calculating it each time

trie_create_data_block may be a rather hot function if a trie is actively
used;  it seems wasteful to re-calculate fill_value each time a new data
block is allocated, considering the fact that it, as well as empty_value,
remains constant after the trie creation.  Let's prematurely optimise it
by pre-calculating the value in trie_create.

* src/trie.h (struct trie): Add fill_value field.
* src/trie.c (trie_create_data_block): Move fill_value calculation...
(trie_create): ...here, assign it to the fill_value field.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/trie.h b/src/trie.h
index 0ec5af226..f82a83aa7 100644
--- a/src/trie.h
+++ b/src/trie.h
@@ -36,6 +36,11 @@
 struct trie {
 	/** Return value of trie_get if key is not found */
 	uint64_t empty_value;
+	/**
+	 * Empty value copied over to fill the whole uint64_t.
+	 * Pre-calculated in trie_create to be used in trie_create_data_block.
+	 */
+	uint64_t fill_value;
 
 	/** Pointer to root node */
 	void *data;