diff --git a/include/sl.h b/include/sl.h
index 88e7f36..91ee9a1 100644
--- a/include/sl.h
+++ b/include/sl.h
@@ -61,10 +61,10 @@
  *
  * A skiplist is a sorted list with O(log(n)) on average for most operations.
  * It is a probabilistic datastructure, meaning that it does not guarantee
- * O(log(n)) it approximates it over time.  This implementation includes
- * improves the probability by integrating the splay list algorithm for
- * rebalancing trading off a bit of computational overhead and code complexity
- * for a nearly always optimal, or "perfect" skiplist.
+ * O(log(n)) it approximates it over time.  This implementation improves the
+ * probability by integrating the splay list algorithm for rebalancing trading
+ * off a bit of computational overhead and code complexity for a nearly always
+ * optimal, or "perfect" skiplist.
  *
  * Conceptually, a skiplist is arranged as follows:
  *
@@ -235,8 +235,8 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
 #define __SKIP_IS_LAST_ENTRY_T2B() if (lvl == 0)
 
 #define __SKIP_ALL_ENTRIES_B2T(field, elm) for (size_t lvl = 0; lvl < slist->slh_max_height; lvl++)
-#define __SKIP_ENTRIES_B2T(field, elm) for (size_t lvl = 0; lvl < elm->field.sle_height; lvl++)
-#define __SKIP_ENTRIES_B2T_FROM(field, elm, off) for (size_t lvl = off; lvl < elm->field.sle_height; lvl++)
+#define __SKIP_ENTRIES_B2T(field, elm) for (size_t lvl = 0; lvl <= elm->field.sle_height; lvl++)
+#define __SKIP_ENTRIES_B2T_FROM(field, elm, off) for (size_t lvl = off; lvl <= elm->field.sle_height; lvl++)
 #define __SKIP_IS_LAST_ENTRY_B2T() if (lvl + 1 == elm->field.sle_height)
 
 /* Iterate over the subtree to the left (v, or 'lt') and right (u) or "CHu" and "CHv". */
@@ -263,6 +263,7 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
     struct decl {                                                                                                                      \
         size_t slh_length, slh_max_height;                                                                                             \
         void *slh_aux;                                                                                                                 \
+        int slh_prng_state;                                                                                                            \
         decl##_node_t *slh_head;                                                                                                       \
         decl##_node_t *slh_tail;                                                                                                       \
         struct {                                                                                                                       \
@@ -289,6 +290,19 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
         size_t pu;           /* sum of hits from intersection to level[1] */                                                           \
     } __skiplist_path_##decl##_t;                                                                                                      \
                                                                                                                                        \
+    /* Xorshift algorithm for PRNG */                                                                                                  \
+    static uint32_t __##decl##_xorshift32(int *state)                                                                                  \
+    {                                                                                                                                  \
+        uint32_t x = *state;                                                                                                           \
+        if (x == 0)                                                                                                                    \
+            x = 123456789;                                                                                                             \
+        x ^= x << 13;                                                                                                                  \
+        x ^= x >> 17;                                                                                                                  \
+        x ^= x << 5;                                                                                                                   \
+        *state = x;                                                                                                                    \
+        return x;                                                                                                                      \
+    }                                                                                                                                  \
+                                                                                                                                       \
     /**                                                                                                                                \
      * -- __skip_compare_entries_fn_                                                                                                   \
      *                                                                                                                                 \
@@ -379,12 +393,12 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
      * Skiplist.  For example, when `max = 6` this function returns 0 with                                                             \
      * probability 0.5, 1 with 0.25, 2 with 0.125, etc. until 6 with 0.5^7.                                                            \
      */                                                                                                                                \
-    static int __skip_toss_##decl(size_t max)                                                                                          \
+    static int __skip_toss_##decl(decl##_t *slist, size_t max)                                                                         \
     {                                                                                                                                  \
         size_t level = 0;                                                                                                              \
         double probability = 0.5;                                                                                                      \
                                                                                                                                        \
-        double random_value = (double)rand() / RAND_MAX; /* NOLINT(*-msc50-cpp) */                                                     \
+        double random_value = (double)__##decl##_xorshift32(&slist->slh_prng_state) / RAND_MAX;                                        \
         while (random_value < probability && level < max) {                                                                            \
             level++;                                                                                                                   \
             probability *= 0.5;                                                                                                        \
@@ -456,9 +470,9 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
          * seed the PRNG in a predictable way and have reproducible random numbers.                                                    \
          */                                                                                                                            \
         if (max < 0)                                                                                                                   \
-            srand(-max);                                                                                                               \
+            slist->slh_prng_state = -max;                                                                                              \
         else                                                                                                                           \
-            srand(((unsigned int)time(NULL) ^ getpid()));                                                                              \
+            slist->slh_prng_state = ((unsigned int)time(NULL) ^ getpid());                                                             \
     fail:;                                                                                                                             \
         return rc;                                                                                                                     \
     }                                                                                                                                  \
@@ -787,7 +801,7 @@ void __attribute__((format(printf, 4, 5))) __skip_diag_(const char *file, int li
             }                                                                                                                          \
             /* Coin toss to determine level of this new node [0, max) */                                                               \
             cur_height = slist->slh_head->field.sle_height;                                                                            \
-            new_height = __skip_toss_##decl(slist->slh_max_height - 1);                                                                \
+            new_height = __skip_toss_##decl(slist, slist->slh_max_height - 1);                                                         \
             new->field.sle_height = new_height;                                                                                        \
             /* Trim the path to at most the new height for the new node. */                                                            \
             for (i = cur_height + 1; i <= new_height; i++) {                                                                           \