1 files changed, 92 insertions, 0 deletions
diff --git a/wsutil/bits_ctz.h b/wsutil/bits_ctz.h
new file mode 100644
index 0000000..b4c43e3
--- /dev/null
+++ b/wsutil/bits_ctz.h
@@ -0,0 +1,92 @@
+/** @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_CTZ_H__
+#define __WSUTIL_BITS_CTZ_H__
+
+#include <inttypes.h>
+
+/* ws_ctz == trailing zeros == position of lowest set bit [0..63] */
+/* ws_ilog2 == position of highest set bit == 63 - leading zeros [0..63] */
+
+/* The return value of both ws_ctz and ws_ilog2 is undefined for x == 0 */
+
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
+
+static inline int
+ws_ctz(uint64_t x)
+{
+	return __builtin_ctzll(x);
+}
+
+static inline int
+ws_ilog2(uint64_t x)
+{
+	return 63 - __builtin_clzll(x);
+}
+
+#else
+
+static inline int
+__ws_ctz32(uint32_t x)
+{
+	/* From http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
+	static const uint8_t table[32] = {
+		0,   1, 28,  2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17,  4, 8,
+		31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18,  6, 11,  5, 10, 9
+	};
+
+	return table[((uint32_t)((x & -(int32_t)x) * 0x077CB531U)) >> 27];
+}
+
+static inline int
+ws_ctz(uint64_t x)
+{
+	uint32_t hi = x >> 32;
+	uint32_t lo = (uint32_t) x;
+
+	if (lo == 0)
+		return 32 + __ws_ctz32(hi);
+	else
+		return __ws_ctz32(lo);
+}
+
+static inline int
+__ws_ilog2_32(uint32_t x)
+{
+	/* From http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn */
+	static const uint8_t table[32] =	{
+		0,  9,  1, 10, 13, 21,  2, 29, 11, 14, 16, 18, 22, 25,  3, 30,
+		8, 12, 20, 28, 15, 17, 24,  7, 19, 27, 23,  6, 26,  5,  4, 31
+	};
+
+	x |= x >> 1;
+	x |= x >> 2;
+	x |= x >> 4;
+	x |= x >> 8;
+	x |= x >> 16;
+
+	return table[((uint32_t)(x * 0x07C4ACDDU)) >> 27];
+}
+
+static inline int
+ws_ilog2(uint64_t x)
+{
+	uint32_t hi = x >> 32;
+	uint32_t lo = (uint32_t) x;
+
+	if (hi == 0)
+		return __ws_ilog2_32(lo);
+	else
+		return 32 + __ws_ilog2_32(hi);
+}
+
+#endif
+
+#endif /* __WSUTIL_BITS_CTZ_H__ */