It handles 0, and could generate better code for that. On Broadwell
architecture, it translates to a single instruction (LZCNT). We're
still on Westmere, so it translates to BSR with a conditional move.
Also, drop unnecessary casts and bit arithmetic, which saves a few
instructions.
Move to header so that it's inlined in parsers.
C++20 introduced two new attributes--likely and unlikely--that
function as a built-in replacement for __builtin_expect implemented
in various compilers. Since it makes code easier to read and it's
an integral part of the language, there's no reason to not use it
instead.
Closesscylladb/scylladb#24786
After fcb8d040 ("treewide: use Software Package Data Exchange
(SPDX) license identifiers"), many dual-licensed files were
left with empty comments on top. Remove them to avoid visual
noise.
Closes#10562
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
At the moment, vint deserialisation is using a naive approach, reading
each byte separately. In practice, vints are going to most often appears
inside larger buffers. That means we can read 8-bytes at a time end then
figure out unneded parts and mask them out. This way we avoid a loop and
do less memory loads which are much more expensive than arithmetic
operations (even if they hit the cache).
Deserialisation function returns a structure containing both the value
and its length in the input buffer. In the vast majority of the cases
the caller will already know the length and having this structure will
make it harder for the compiler to emit good code, especially if the
function is not inlined.
In practice I've seen the structure causing register pressure problems
that lead to spilling variables to memory.
Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
This method takes first byte and determins how many bytes
are used to represent an unsigned variant integer.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Version 5 of the native protocol for CQL [1] adds the `vint` and `unsigned vint`
types.
An unsigned integer encoded as a `vint` has a variable size based on the
magnitude of the value. The first byte indicates the total number of bytes.
For signed integers, a "zig-zag" encoding scheme ensures that small negative
values are encoded as short-length `vint`s (0 -> 0, -1 -> 1, 1 -> 2, 2 -> 3, -2
-> 4, etc).
[1] https://github.com/apache/cassandra/blob/trunk/doc/native_protocol_v5.spec
