1 files changed, 15 insertions, 0 deletions
diff --git a/stc/cbitset.h b/stc/cbitset.h
index 7f2c2c39..c6311080 100644
--- a/stc/cbitset.h
+++ b/stc/cbitset.h
@@ -48,6 +48,13 @@ int main() {
 #include <assert.h>
 #include "cdefs.h"
 
+#if defined(__GNUC__)
+#define cbitset_popcnt64(i) __builtin_popcountll(i)
+#else
+#include <nmmintrin.h>
+#define cbitset_popcnt64(i) _mm_popcnt_u64(i)
+#endif
+
 typedef struct { uint64_t* _arr; size_t size; } CBitset;
 
 #define cbitset_init {NULL, 0}
@@ -87,6 +94,14 @@ STC_INLINE void cbitset_flip(CBitset *self, size_t i) {
 STC_INLINE bool cbitset_test(CBitset set, size_t i) {
     return (set._arr[i >> 6] & (1ull << (i & 63))) != 0;
 }
+STC_INLINE size_t cbitset_count(CBitset set) {
+    size_t count = 0, n = (set.size + 63) >> 6;
+    if (set.size > 0) {
+        --n; for (size_t i=0; i<n; ++i) count += cbitset_popcnt64(set._arr[i]);
+        count += cbitset_popcnt64(set._arr[n] & ((1ull << (set.size & 63)) - 1));
+    }
+    return count;
+}
 
 STC_INLINE void cbitset_setAll(CBitset *self, bool value) {
     memset(self->_arr, value ? 0xff : 0x0, ((self->size + 63) >> 6) * 8);