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llvm-project/libcxx/include
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Jorg Brown 586952f4ce Optimize std::midpoint for integers 
Same idea as the current algorithm, that is, add (half of the difference between a and b) to a.

But we use a different technique for computing the difference: we compute b - a into a pair of integers that are named "sign_bit" and "diff". We have to use a pair because subtracting two 32-bit integers produces a 33-bit result.

Computing half of that is a simple matter of shifting diff right by 1, and adding sign_bit shifted left by 31. llvm knows how to do that with one instruction: shld.

The only tricky part is that if the difference is odd and negative, then shifting it by one isn't the same as dividing it by two - shifting a negative one produces a negative one, for example. So there's one more adjustment: if the sign bit and the low bit of diff are one, we add one.

For a demonstration of the codegen difference, see https://godbolt.org/z/7ar3K9 , which also has a built-in test.

Differential Revision: https://reviews.llvm.org/D69459
2019-11-04 19:00:23 -08:00
..
experimental
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
ext
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
support
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
__bit_reference
Reorganize the 'bit' header to make most of the facilities available for internal use pre-C++20. NFC for external users
2019-07-12 01:01:55 +00:00
__bsd_locale_defaults.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__bsd_locale_fallbacks.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__config
Refine check for _LIBCPP_C_HAS_NO_GETS on FreeBSD
2019-10-19 10:59:23 +00:00
__config_site.in
[libc++] Take 2: Integrate the PSTL into libc++
2019-08-05 18:29:14 +00:00
__debug
[libc++][NFC] Remove excess trailing newlines from most files
2019-10-23 08:08:57 -07:00
__errc
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__functional_03
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__functional_base
[libc++] Take 2: Implement LWG 2510
2019-09-26 14:51:10 +00:00
__functional_base_03
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__hash_table
Reorganize the 'bit' header to make most of the facilities available for internal use pre-C++20. NFC for external users
2019-07-12 01:01:55 +00:00
__libcpp_version
Bump the trunk version to 10.0.0svn
2019-07-18 11:51:05 +00:00
__locale
[libcxx] Fix build breakage on mips
2019-08-20 10:19:55 +00:00
__mutex_base
[libc++] Take 2: Implement LWG 2510
2019-09-26 14:51:10 +00:00
__node_handle
Avoid name conflict with kernel headers
2019-04-24 09:43:44 +00:00
__nullptr
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__split_buffer
Improve codegen for deque.
2019-08-12 07:51:05 +00:00
__sso_allocator
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__std_stream
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
__string
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
__threading_support
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
__tree
Fix memory leak in set and map.
2019-07-11 23:13:38 +00:00
__tuple
Refactor default constructor SFINAE in pair and tuple.
2019-09-30 20:55:30 +00:00
__undef_macros
Update the file headers across all of the LLVM projects in the monorepo
2019-01-19 08:50:56 +00:00
algorithm
Add a missing _VSTD:: before a call to merge. Fixes PR43034. Checked the rest of 'algorithm' looking for unqualified calls. Didn't find any.
2019-08-20 22:23:35 +00:00
any
[NFC][libc++] Remove stray semi-colon after function definition
2019-06-19 16:33:28 +00:00
array
[libc++] Declare std::tuple_element as struct instead of class
2019-04-01 16:39:34 +00:00
atomic
[libc++] Use __extension__ in a portable manner
2019-09-04 12:44:19 +00:00
bit
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
bitset
Ensure bitset's string constructor doesn't poison the overload set.
2019-07-01 19:59:34 +00:00
cassert
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
ccomplex
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cctype
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cerrno
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cfenv
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cfloat
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
charconv
[libc++] Fix build with gcc 4.8
2019-06-13 22:27:24 +00:00
chrono
Revert "Extension: Mark the default constructor of chrono::duration as conditionally noexcept"; this breaks the gcc5 bot for C++11
2019-09-23 06:16:41 +00:00
cinttypes
Update the file headers across all of the LLVM projects in the monorepo
2019-01-19 08:50:56 +00:00
ciso646
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
climits
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
clocale
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
CMakeLists.txt
[NFC] Fix typos in CMake comment
2019-10-21 23:38:32 +00:00
cmath
[libc++] Harden usage of static_assert against C++03
2019-10-01 12:12:21 +00:00
codecvt
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
compare
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
complex
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
complex.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
condition_variable
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
csetjmp
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
csignal
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstdarg
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstdbool
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstddef
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstdint
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstdio
Remove ::gets for FreeBSD 13 and later
2019-09-07 22:18:20 +00:00
cstdlib
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cstring
Update the file headers across all of the LLVM projects in the monorepo
2019-01-19 08:50:56 +00:00
ctgmath
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
ctime
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
ctype.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cwchar
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
cwctype
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
deque
Improve codegen for deque.
2019-08-12 07:51:05 +00:00
errno.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
exception
Make move and forward work in C++03.
2019-06-21 15:20:55 +00:00
execution
[pstl][libc++] Provide uglified header names for interface headers
2019-08-06 21:11:24 +00:00
fenv.h
Mark fenv.h as a system header before the #include_next directive
2019-03-29 16:03:57 +00:00
filesystem
[libc++] Always build with -fvisibility=hidden
2019-08-13 15:02:53 +00:00
float.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
forward_list
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
fstream
Open fstream files in O_CLOEXEC mode when possible.
2019-09-16 19:26:41 +00:00
functional
Revert "Suppress -Wctad-maybe-unsupported on types w/o deduction guides."
2019-08-04 07:13:43 +00:00
future
Assume __is_final, __is_base_of, and friends.
2019-06-21 13:56:13 +00:00
initializer_list
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
inttypes.h
AIX system headers need stdint.h and inttypes.h to be re-enterable
2019-06-20 15:36:32 +00:00
iomanip
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
ios
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
iosfwd
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
iostream
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
istream
[libc++] Implement LWG 3199
2019-08-20 18:21:06 +00:00
iterator
Revert "Suppress -Wctad-maybe-unsupported on types w/o deduction guides."
2019-08-04 07:13:43 +00:00
limits
Fix -Wdouble-promotion warnings.
2019-07-01 16:13:31 +00:00
limits.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
list
[NFC] Strip trailing whitespace from libc++
2019-10-23 11:19:19 -07:00
locale
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
locale.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
map
[libc++] Use _EnableIf instead of std::enable_if in deduction guides for map and set
2019-07-19 17:13:39 +00:00
math.h
[libc++] Move __clamp_to_integral to <cmath>, and harden against min()/max() macros
2019-09-04 13:35:03 +00:00
memory
[libcxx] Remove shared_ptr::make_shared
2019-10-22 15:16:49 +00:00
module.modulemap
[libc++] Take 2: Integrate the PSTL into libc++
2019-08-05 18:29:14 +00:00
mutex
[libc++] Take 2: Implement LWG 2510
2019-09-26 14:51:10 +00:00
new
[libc++] Take 2: Implement LWG 2510
2019-09-26 14:51:10 +00:00
numeric
Optimize std::midpoint for integers
2019-11-04 19:00:23 -08:00
optional
Add a missing '__uncvref_t' to the SFINAE constraints for optional's assignment operator. Fixes PR38638. Thanks to Jonathan Wakely for the report
2019-06-27 18:40:55 +00:00
ostream
Add forward declaration of operator<< in <string_view> as required.
2019-09-25 18:56:54 +00:00
queue
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
random
[libc++] Explicitly cast in generate_canonical
2019-08-20 15:39:20 +00:00
ratio
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
regex
Add a missing default parameter to regex::assign. This is LWG3296; reviewed as https://reviews.llvm.org/D67944
2019-09-25 16:40:30 +00:00
scoped_allocator
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
set
[libc++] Use _EnableIf instead of std::enable_if in deduction guides for map and set
2019-07-19 17:13:39 +00:00
setjmp.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
shared_mutex
Revert "Suppress -Wctad-maybe-unsupported on types w/o deduction guides."
2019-08-04 07:13:43 +00:00
span
[libc++] Declare std::tuple_element as struct instead of class
2019-04-01 16:39:34 +00:00
sstream
add a test and a couple minor bug fixes for the implicit-signed-integer-truncation sanitizer. This is PR#40566
2019-02-01 21:59:27 +00:00
stack
[NFC][libcxx] Remove trailing whitespace
2019-05-29 16:01:36 +00:00
stdbool.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
stddef.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
stdexcept
Fix ABI compatibility of <stdexcept> with VCRuntime.
2019-03-06 20:31:57 +00:00
stdint.h
AIX system headers need stdint.h and inttypes.h to be re-enterable
2019-06-20 15:36:32 +00:00
stdio.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
stdlib.h
Fix implementation of ::abs and std::abs LWG 2192.
2019-04-23 18:01:58 +00:00
streambuf
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
string
Optimize operator=(const basic_string&) for tail call.
2019-10-09 03:07:02 +00:00
string_view
Add forward declaration of operator<< in <string_view> as required.
2019-09-25 18:56:54 +00:00
string.h
Update the file headers across all of the LLVM projects in the monorepo
2019-01-19 08:50:56 +00:00
strstream
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
system_error
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
tgmath.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
thread
Rework recursive_timed_mutex so that it uses __thread_id instead of using the lower-level __libcpp_thread_id. This is prep for fixing PR42918. Reviewed as https://reviews.llvm.org/D65895
2019-08-14 16:21:27 +00:00
tuple
PR43764: Qualify a couple of calls to forward_as_tuple to be ADL-resilient.
2019-10-28 18:04:41 -07:00
type_traits
[libc++] Add test and remove workaround for PR13592
2019-10-30 15:52:11 -07:00
typeindex
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
typeinfo
Fix build breakage on 32-bit machines
2019-05-29 02:38:19 +00:00
unordered_map
Add contains method to associative containers. This patch implements P0458R2, adding contains to map, multimap, unordered_map, unordered_multimap, set, multiset, unordered_set, and unordered_multiset.
2019-07-16 03:21:01 +00:00
unordered_set
Add contains method to associative containers. This patch implements P0458R2, adding contains to map, multimap, unordered_map, unordered_multimap, set, multiset, unordered_set, and unordered_multiset.
2019-07-16 03:21:01 +00:00
utility
Refactor default constructor SFINAE in pair and tuple.
2019-09-30 20:55:30 +00:00
valarray
Remove incorrect explicit instantiation declarations for valarray
2019-04-25 21:31:58 +00:00
variant
Improve compile time of variant.
2019-07-14 21:29:39 +00:00
vector
Recommit r370502: Make vector unconditionally move elements when
2019-09-13 16:09:33 +00:00
version
P0722R3: Implement library support for destroying delete
2019-05-23 23:46:44 +00:00
wchar.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00
wctype.h
Update more file headers across all of the LLVM projects in the monorepo
2019-01-19 10:56:40 +00:00