diff --git a/m-bitset.h b/m-bitset.h
index ee7e4e56..68a3727e 100644
--- a/m-bitset.h
+++ b/m-bitset.h
@@ -34,6 +34,8 @@
 #include "m-core.h"
 #include "m-string.h"   // Only for bitset_get_str function.
 
+/********************************** INTERNAL ************************************/
+
 // Define a limb of a bitset
 typedef unsigned int bitset_limb;
 #define BITSET_LIMB_BIT (sizeof(bitset_limb) * CHAR_BIT)
@@ -41,18 +43,22 @@ typedef unsigned int bitset_limb;
 typedef struct bitset_s {
   size_t size;            // Size is the number of bits
   size_t alloc;           // Alloc is the number of allocated limbs
-  bitset_limb *ptr;
+  bitset_limb *ptr;       // Pointer to the allocated limbs
 } bitset_t[1];
 
 typedef struct bitset_it_s {
-  size_t index;
-  bool   value;
-  struct bitset_s *set;
+  size_t index;           // index to the array of bit
+  bool   value;           // value used for _ref & _cref to store the value
+  struct bitset_s *set;   // the associated bitset
 } bitset_it_t[1];
 
-// Compute alloc from size.
+// bitset grow policy
 #define BITSETI_INC_ALLOC_SIZE(n) ((n) < 2 ? 4 : (n) * 2)
+
+// Compute the number of allocated limbs needed to handle 'n' bits.
 #define BITSETI_TO_ALLOC(n)       (((n) + BITSET_LIMB_BIT - 1) / BITSET_LIMB_BIT)
+
+// Compute the number of bits available from the allocated size
 #define BITSETI_FROM_ALLOC(n)     ((n) * BITSET_LIMB_BIT)
 
 #define BITSETI_CONTRACT(t)                             \
@@ -60,6 +66,9 @@ typedef struct bitset_it_s {
   assert (t->size <= BITSETI_FROM_ALLOC (t->alloc));    \
   assert (t->size == 0 || t->ptr != NULL);
 
+
+/********************************** EXTERNAL ************************************/
+
 static inline void
 bitset_init(bitset_t t)
 {
@@ -67,6 +76,7 @@ bitset_init(bitset_t t)
   assert (M_POWEROF2_P(BITSET_LIMB_BIT));
   t->size = t->alloc = 0;
   t->ptr = NULL;
+  BITSETI_CONTRACT(t);
 }
 
 static inline void
@@ -81,6 +91,7 @@ bitset_clear(bitset_t t)
 {
   bitset_clean(t);
   M_MEMORY_FREE(t->ptr);
+  // This is not really needed, but is safer
   t->alloc = 0;
   t->ptr = NULL;
 }
@@ -154,11 +165,14 @@ bitset_push_back (bitset_t v, bool x)
   BITSETI_CONTRACT (v);
   if (v->size >= BITSETI_FROM_ALLOC (v->alloc)) {
     const size_t needAlloc = BITSETI_INC_ALLOC_SIZE(v->alloc);
+    // Check for integer overflow
     if (M_UNLIKELY (needAlloc <= v->alloc)) {
       M_MEMORY_FULL(needAlloc * sizeof(bitset_limb));
       return;
     }
+    // Alloc memory
     bitset_limb *ptr = M_MEMORY_REALLOC (bitset_limb, v->ptr, needAlloc);
+    // Check if success
     if (M_UNLIKELY (ptr == NULL) ) {
       M_MEMORY_FULL(needAlloc * sizeof(bitset_limb));
       return;
diff --git a/tests/Makefile b/tests/Makefile
index b60a7823..aa8d81ce 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -88,6 +88,9 @@ gene-array:
 gene-shared:
 	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-shared.c && less tgen-shared.s
 
+gene-bitset:
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-bitset.c && less tgen-bitset.s
+
 
 #####################################################################################################
 # Code analyzer tools
diff --git a/tests/tgen-bitset.c b/tests/tgen-bitset.c
new file mode 100644
index 00000000..05cced71
--- /dev/null
+++ b/tests/tgen-bitset.c
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2017, Patrick Pelissier
+ * All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * + Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * + Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include "m-bitset.h"
+
+void f_b(bitset_t s, size_t i, bool b)
+{
+  bitset_set_at(s, i, b);
+}
+
+void f_0(bitset_t s, size_t i)
+{
+  bitset_set_at(s, i, false);
+}
+
+void f_1(bitset_t s, size_t i)
+{
+  bitset_set_at(s, i, true);
+}
+
+