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diff --git a/wsutil/bits_count_ones.h b/wsutil/bits_count_ones.h
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+/** @file
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef __WSUTIL_BITS_COUNT_ONES_H__
+#define __WSUTIL_BITS_COUNT_ONES_H__
+
+#include <inttypes.h>
+
+/*
+ * The variable-precision SWAR algorithm is an interesting way to count
+ * the number of bits set in an integer:
+ *
+ *     https://www.playingwithpointers.com/blog/swar.html
+ *
+ * See
+ *
+ *     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36041
+ *     https://danluu.com/assembly-intrinsics/
+ *
+ * for discussions of various forms of population-counting code on x86.
+ *
+ * See
+ *
+ *     https://docs.microsoft.com/en-us/cpp/intrinsics/popcnt16-popcnt-popcnt64
+ *
+ * for MSVC's population count intrinsics.
+ *
+ * Note that not all x86 processors support the POPCOUNT instruction.
+ *
+ * Other CPUs may have population count instructions as well.
+ */
+
+static inline int
+ws_count_ones(const uint64_t x)
+{
+	uint64_t bits = x;
+
+	bits = bits - ((bits >> 1) & G_GUINT64_CONSTANT(0x5555555555555555));
+	bits = (bits & G_GUINT64_CONSTANT(0x3333333333333333)) + ((bits >> 2) & G_GUINT64_CONSTANT(0x3333333333333333));
+	bits = (bits + (bits >> 4)) & G_GUINT64_CONSTANT(0x0F0F0F0F0F0F0F0F);
+
+	return (int)((bits * G_GUINT64_CONSTANT(0x0101010101010101)) >> 56);
+}
+
+#endif /* __WSUTIL_BITS_COUNT_ONES_H__ */