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-rw-r--r--fs/bcachefs/varint.c129
1 files changed, 129 insertions, 0 deletions
diff --git a/fs/bcachefs/varint.c b/fs/bcachefs/varint.c
new file mode 100644
index 0000000000..cb4f33ed9a
--- /dev/null
+++ b/fs/bcachefs/varint.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/math.h>
+#include <linux/string.h>
+#include <asm/unaligned.h>
+
+#ifdef CONFIG_VALGRIND
+#include <valgrind/memcheck.h>
+#endif
+
+#include "varint.h"
+
+/**
+ * bch2_varint_encode - encode a variable length integer
+ * @out: destination to encode to
+ * @v: unsigned integer to encode
+ * Returns: size in bytes of the encoded integer - at most 9 bytes
+ */
+int bch2_varint_encode(u8 *out, u64 v)
+{
+ unsigned bits = fls64(v|1);
+ unsigned bytes = DIV_ROUND_UP(bits, 7);
+ __le64 v_le;
+
+ if (likely(bytes < 9)) {
+ v <<= bytes;
+ v |= ~(~0 << (bytes - 1));
+ v_le = cpu_to_le64(v);
+ memcpy(out, &v_le, bytes);
+ } else {
+ *out++ = 255;
+ bytes = 9;
+ put_unaligned_le64(v, out);
+ }
+
+ return bytes;
+}
+
+/**
+ * bch2_varint_decode - encode a variable length integer
+ * @in: varint to decode
+ * @end: end of buffer to decode from
+ * @out: on success, decoded integer
+ * Returns: size in bytes of the decoded integer - or -1 on failure (would
+ * have read past the end of the buffer)
+ */
+int bch2_varint_decode(const u8 *in, const u8 *end, u64 *out)
+{
+ unsigned bytes = likely(in < end)
+ ? ffz(*in & 255) + 1
+ : 1;
+ u64 v;
+
+ if (unlikely(in + bytes > end))
+ return -1;
+
+ if (likely(bytes < 9)) {
+ __le64 v_le = 0;
+
+ memcpy(&v_le, in, bytes);
+ v = le64_to_cpu(v_le);
+ v >>= bytes;
+ } else {
+ v = get_unaligned_le64(++in);
+ }
+
+ *out = v;
+ return bytes;
+}
+
+/**
+ * bch2_varint_encode_fast - fast version of bch2_varint_encode
+ * @out: destination to encode to
+ * @v: unsigned integer to encode
+ * Returns: size in bytes of the encoded integer - at most 9 bytes
+ *
+ * This version assumes it's always safe to write 8 bytes to @out, even if the
+ * encoded integer would be smaller.
+ */
+int bch2_varint_encode_fast(u8 *out, u64 v)
+{
+ unsigned bits = fls64(v|1);
+ unsigned bytes = DIV_ROUND_UP(bits, 7);
+
+ if (likely(bytes < 9)) {
+ v <<= bytes;
+ v |= ~(~0 << (bytes - 1));
+ } else {
+ *out++ = 255;
+ bytes = 9;
+ }
+
+ put_unaligned_le64(v, out);
+ return bytes;
+}
+
+/**
+ * bch2_varint_decode_fast - fast version of bch2_varint_decode
+ * @in: varint to decode
+ * @end: end of buffer to decode from
+ * @out: on success, decoded integer
+ * Returns: size in bytes of the decoded integer - or -1 on failure (would
+ * have read past the end of the buffer)
+ *
+ * This version assumes that it is safe to read at most 8 bytes past the end of
+ * @end (we still return an error if the varint extends past @end).
+ */
+int bch2_varint_decode_fast(const u8 *in, const u8 *end, u64 *out)
+{
+#ifdef CONFIG_VALGRIND
+ VALGRIND_MAKE_MEM_DEFINED(in, 8);
+#endif
+ u64 v = get_unaligned_le64(in);
+ unsigned bytes = ffz(*in) + 1;
+
+ if (unlikely(in + bytes > end))
+ return -1;
+
+ if (likely(bytes < 9)) {
+ v >>= bytes;
+ v &= ~(~0ULL << (7 * bytes));
+ } else {
+ v = get_unaligned_le64(++in);
+ }
+
+ *out = v;
+ return bytes;
+}