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
So we can use it for defining other small_vector
deriving their internal capacity from another small_vector
type.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Rewrite
_begin + n > _capacity_end
as
n > _capacity_end - _begin
and then as
n > capacity()
for two reasons:
- The last form is easier to read than the first form.
- Per N4950 (the final C++23 working draft), [expr.add] paragraph 4, the
expression
_begin + n (i.e., P + J)
is defined only if
0 ≤ 0 + n ≤ _capacity_end - _begin (i.e., 0 ≤ i + j ≤ n)
equivalently, only if
_begin ≤ _begin + n ≤ _capacity_end
Therefore, the expression
_begin + n
invokes undefined behavior exactly when we'd expect our check
_begin + n > _capacity_end
to evaluate to true.
gcc and clang have been aggressively equating undefined behavior to "never
happens"; let's prevent that here.
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>
Closesscylladb/scylladb#21213
std::ranges::to<>() has a little protocol with containers to
allow them to optimize their construction from ranges. Implement it
for small_vector. It optimizes ranges that can have their size determined
quickly, or that can be traversed twice to determine the size by reserving
up front. Single-pass ranges (std::ranges::input_range) use the less
efficient push_back method.
A unit test (which fails without the new constructor) is added.
Closesscylladb/scylladb#21094
since we do not rely on FMT_DEPRECATED_OSTREAM to define the
fmt::formatter for us anymore, let's stop defining `FMT_DEPRECATED_OSTREAM`.
in this change,
* utils: drop the range formatters in to_string.hh and to_string.c, as
we don't use them anymore. and the tests for them in
test/boost/string_format_test.cc are removed accordingly.
* utils: use fmt to print chunk_vector and small_vector. as
we are not able to print the elements using operator<< anymore
after switching to {fmt} formatters.
* test/boost: specialize fmt::details::is_std_string_like<bytes>
due to a bug in {fmt} v9, {fmt} fails to format a range whose
element type is `basic_sstring<uint8_t>`, as it considers it
as a string-like type, but `basic_sstring<uint8_t>`'s char type
is signed char, not char. this issue does not exist in {fmt} v10,
so, in this change, we add a workaround to explicitly specialize
the type trait to assure that {fmt} format this type using its
`fmt::formatter` specialization instead of trying to format it
as a string. also, {fmt}'s generic ranges formatter calls the
pair formatter's `set_brackets()` and `set_separator()` methods
when printing the range, but operator<< based formatter does not
provide these method, we have to include this change in the change
switching to {fmt}, otherwise the change specializing
`fmt::details::is_std_string_like<bytes>` won't compile.
* test/boost: in tests, we use `BOOST_REQUIRE_EQUAL()` and its friends
for comparing values. but without the operator<< based formatters,
Boost.Test would not be able to print them. after removing
the homebrew formatters, we need to use the generic
`boost_test_print_type()` helper to do this job. so we are
including `test_utils.hh` in tests so that we can print
the formattable types.
* treewide: add "#include "utils/to_string.hh" where
`fmt::formatter<optional<>>` is used.
* configure.py: do not define FMT_DEPRECATED_OSTREAM
* cmake: do not define FMT_DEPRECATED_OSTREAM
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
As seen in https://github.com/scylladb/scylladb/issues/13146
the current implementation is not general enough
to provide print helpers for all kind of containers.
Modernize the implementation using templates based
on std::ranges::range and using fmt::join.
Extend unit test for formatting different types of ranges,
boost::transformed ranges, deque.
Fixes#13146
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
small_vector should be feature-wise compatible with std::vector<>,
let's add operator<=> for it.
also, there is not needd to define operator!=() explicitly, C++20
define this for us if operator==() is defined, so let's drop it.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13032
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
The copy constructor of small vector has a noexcept specifier, however
it calls `reserve(size_t)`, which can throw `std::bad_alloc`. This
causes issues when using it inside tests that use
alloc_failure_injector, but potentially could also float up in the
production.
Closes#9338
small_vector is a variation of std::vector<> that reserves a configurable
amount of storage internally, without the need for memory allocation.
This can bring measurable gains if the expected number of elements is
small. The drawback is that moving such small_vector is more expensive
and invalidates iterators as well as references which disqualifies it in
some cases.
