1 files changed, 62 insertions, 0 deletions
diff --git a/src/bits.c b/src/bits.c
new file mode 100644
index 0000000..6462d21
--- /dev/null
+++ b/src/bits.c
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: copyleft-next-0.3.1 */
+/* Copyright 2021 - 2022, Kim Kuparinen < kimi.h.kuparinen@gmail.com > */
+
+/**
+ * @file bits.c
+ * Bit manipulation helper implementations, currently just byte swaps.
+ */
+
+#include <kmi/types.h>
+#include <kmi/attrs.h>
+#include <kmi/bits.h>
+#include <kmi/builtin.h>
+
+#undef __bswap16
+__weak uint16_t __bswap16(const uint16_t u)
+{
+	return (u & 0xff00) >> 8 | (u & 0x00ff) << 8;
+}
+
+#undef __bswap32
+__weak uint32_t __bswap32(const uint32_t u)
+{
+	return (u & 0xff000000) >> 24 | (u & 0x00ff0000) >> 8 |
+	       (u & 0x0000ff00) << 8 | (u & 0x000000ff) << 24;
+}
+
+#undef __bswap64
+__weak uint64_t __bswap64(const uint64_t u)
+{
+	return (u & 0xff00000000000000ULL) >> 56 |
+	       (u & 0x00ff000000000000ULL) >> 40 |
+	       (u & 0x0000ff0000000000ULL) >> 24 |
+	       (u & 0x000000ff00000000ULL) >> 8 |
+	       (u & 0x00000000ff000000ULL) << 8 |
+	        (u & 0x0000000000ff0000ULL) << 24 |
+	        (u & 0x000000000000ff00ULL) << 40 |
+	        (u & 0x00000000000000ffULL) << 56;
+}
+
+#undef ffs
+__weak int ffs(int v)
+{
+	/* http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightParallel */
+	if (v == 0)
+		return 0;
+
+	/* silence ubsan warning */
+	if (v == INT_MIN)
+		return 32;
+
+	int c = 32;
+	v &= -v;
+
+	if (v) c--;
+	if (v & 0x0000FFFF) c -= 16;
+	if (v & 0x00FF00FF) c -= 8;
+	if (v & 0x0F0F0F0F) c -= 4;
+	if (v & 0x33333333) c -= 2;
+	if (v & 0x55555555) c -= 1;
+
+	return c + 1;
+}