adding a trim function

include/bitset.h

@@ -67,6 +67,9 @@ static inline bool bitset_grow( bitset_t *bitset,  size_t newarraysize ) {
   return true; // success!
 }
 
+/* attempts to recover unused memory, return false in case of reallocation failure */
+bool bitset_trim(bitset_t *bitset); 
+
 
 /* Set the ith bit. Attempts to resize the bitset if needed (may silently fail) */
 static inline void bitset_set(bitset_t *bitset,  size_t i ) {

src/bitset.c

@@ -255,3 +255,36 @@ size_t  bitset_symmetric_difference_count(const bitset_t *restrict b1, const bit
   }
   return answer;
 }
+
+/* Grow the bitset so that it can support newarraysize * 64 bits with padding. Return true in case of success, false for failure. */
+static inline bool bitset_grow( bitset_t *bitset,  size_t newarraysize ) {
+  if (bitset->capacity < newarraysize) {
+    uint64_t *newarray;
+    bitset->capacity = newarraysize * 2;
+    if ((newarray = (uint64_t *) realloc(bitset->array, sizeof(uint64_t) * bitset->capacity)) == NULL) {
+      free(bitset->array);
+      return false;
+    }
+    bitset->array = newarray;
+  }
+  memset(bitset->array + bitset->arraysize ,0,sizeof(uint64_t) * (newarraysize - bitset->arraysize));
+  bitset->arraysize = newarraysize;
+  return true; // success!
+}
+
+bool bitset_trim(bitset_t * bitset) {
+  size_t newsize = bitset->arraysize;
+  while(newsize > 0) {
+    if(bitset->array[newsize - 1] == 0) newsize -= 1;
+  }
+  if(bitset->capacity == newsize) return true; // nothing to do
+  bitset->capacity = newsize;
+  bitset->arraysize = newsize;
+  uint64_t *newarray;
+  if ((newarray = (uint64_t *) realloc(bitset->array, sizeof(uint64_t) * bitset->capacity)) == NULL) {
+      free(bitset->array);
+      return false;
+  }
+  bitset->array = newarray;
+  return true;
+}