sys: Add popcnt() implementation

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/sys/include/sys/bitops.h b/sys/include/sys/bitops.h
new file mode 100644
index 0000000..e8e9567
--- /dev/null
+++ b/sys/include/sys/bitops.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_BITOPS_H_
+#define _SYS_BITOPS_H_
+
+#include <sys/cdefs.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 int
+popcnt(uint64_t x)
+{
+    x -= (x >> 1) & BOPS_M1;
+    x =  (x & BOPS_M2) + ((x >> 2) & BOPS_M2);
+    x =  (x + (x >> 4)) & BOPS_M4;
+    return (x * BOPS_H0) >> 56;
+}
+
+#endif  /* !_SYS_BITOPS_H_ */