add function skiplist_get_proper_level

HISTORY

@@ -1,5 +1,5 @@
 
-Version 1.44  2020-09-30
+Version 1.44  2020-10-10
   * add test file src/tests/test_pthread_lock.c
   * add uniq_skiplist.[hc]
   * add function split_string_ex

src/flat_skiplist.h

@@ -85,6 +85,15 @@ static inline void *flat_skiplist_next(FlatSkiplistIterator *iterator)
     return data;
 }
 
+static inline void *flat_skiplist_get_first(FlatSkiplist *sl)
+{
+    if (sl->top->links[0] != sl->tail) {
+        return sl->top->links[0]->data;
+    } else {
+        return NULL;
+    }
+}
+
 static inline bool flat_skiplist_empty(FlatSkiplist *sl)
 {
     return sl->top->links[0] == sl->tail;

src/multi_skiplist.h

@@ -110,6 +110,15 @@ static inline void *multi_skiplist_next(MultiSkiplistIterator *iterator)
     return data;
 }
 
+static inline void *multi_skiplist_get_first(MultiSkiplist *sl)
+{
+    if (sl->top->links[0] != sl->tail) {
+        return sl->top->links[0]->head->data;
+    } else {
+        return NULL;
+    }
+}
+
 static inline bool multi_skiplist_empty(MultiSkiplist *sl)
 {
     return sl->top->links[0] == sl->tail;

src/skiplist_common.h

@@ -21,6 +21,31 @@
 typedef int (*skiplist_compare_func)(const void *p1, const void *p2);
 typedef void (*skiplist_free_func)(void *ptr);
 
+static inline int skiplist_get_proper_level(const int target_count)
+{
+    if (target_count < 8) {
+        return 2;
+    } else if (target_count < 64) {
+        return 4;
+    } else if (target_count < 256) {
+        return 6;
+    } else if (target_count < 1024) {
+        return 8;
+    } else if (target_count < 4096) {
+        return 10;
+    } else if (target_count < 16 * 1024) {
+        return 12;
+    } else if (target_count < 64 * 1024) {
+        return 14;
+    } else if (target_count < 256 * 1024) {
+        return 16;
+    } else if (target_count < 1024 * 1024) {
+        return 18;
+    } else {
+        return 20;
+    }
+}
+
 #ifdef __cplusplus
 extern "C" {
 #endif

src/skiplist_set.h

@@ -81,6 +81,15 @@ static inline void *skiplist_set_next(SkiplistSetIterator *iterator)
     return data;
 }
 
+static inline void *skiplist_set_get_first(SkiplistSet *sl)
+{
+    if (sl->top->links[0] != sl->tail) {
+        return sl->top->links[0]->data;
+    } else {
+        return NULL;
+    }
+}
+
 static inline bool skiplist_set_empty(SkiplistSet *sl)
 {
     return sl->top->links[0] == sl->tail;