Add quick_insert_value for optimized hash insertion

Reduces the number of reads by two

Co-authored-by: Brian Pane <brianp@brianp.net>

trifectatechfoundation/zlib-rs#374
trifectatechfoundation/zlib-rs#375

1 files changed, 22 insertions, 0 deletions

diff --git a/insert_string_tpl.h b/insert_string_tpl.h
index eac1bfe045..64cc743458 100644
--- a/insert_string_tpl.h
+++ b/insert_string_tpl.h
@@ -52,6 +52,28 @@ Z_INTERNAL uint32_t UPDATE_HASH(uint32_t h, uint32_t val) {
 }
 
 /* ===========================================================================
+ * Quick insert string str in the dictionary using a pre-read value and set match_head
+ * to the previous head of the hash chain (the most recent string with same hash key).
+ * Return the previous length of the hash chain.
+ */
+Z_INTERNAL Pos QUICK_INSERT_VALUE(deflate_state *const s, uint32_t str, uint32_t val) {
+    uint32_t hm;
+    Pos head;
+
+    HASH_CALC_VAR_INIT;
+    HASH_CALC(HASH_CALC_VAR, val);
+    HASH_CALC_VAR &= HASH_CALC_MASK;
+    hm = HASH_CALC_VAR;
+
+    head = s->head[hm];
+    if (LIKELY(head != str)) {
+        s->prev[str & s->w_mask] = head;
+        s->head[hm] = (Pos)str;
+    }
+    return head;
+}
+
+/* ===========================================================================
  * Quick insert string str in the dictionary and set match_head to the previous head
  * of the hash chain (the most recent string with same hash key). Return
  * the previous length of the hash chain.