sdk: Add bit operations header with PopCnt

Signed-off-by: Chloe M. <chloe@mensia.org>

sdk/head/bitops.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: Pool allocator
+ * Author:      Chloe M.
+ */
+
+#ifndef _SDK_BITOPS_H_
+#define _SDK_BITOPS_H_ 1
+
+#include <stdef.h>
+
+#define BOPS_M1  0x5555555555555555ULL /* 01010101... */
+#define BOPS_M2  0x3333333333333333ULL /* 00110011... */
+#define BOPS_M4  0x0F0F0F0F0F0F0F0FULL /* 00001111... */
+#define BOPS_M8  0x00FF00FF00FF00FFULL /* x4(0), x4(1) */
+#define BOPS_M16 0x0000FFFF0000FFFFULL /* x16(0), x16(1) */
+#define BOPS_M32 0x00000000FFFFFFFFULL /* x32(0), x32(1) */
+#define BOPS_H0  0x0101010101010101ULL /* sum of 256^{0,1,2,3...} */
+
+ALWAYS_INLINE static inline LONG
+PopCnt(UQUAD Value)
+{
+    Value -= (Value >> 1) & BOPS_M1;
+    Value =  (Value & BOPS_M2) + ((Value >> 2) & BOPS_M2);
+    Value =  (Value + (Value >> 4)) & BOPS_M4;
+    return (Value * BOPS_H0) >> 56;
+}
+
+#endif  /* !_SDK_BITOPS_H_ */