1) Inline EncodeFixed{32,64}(). They emit single machine instructions on 64-bit processors.
2) Remove size narrowing compiler warnings from DecodeFixed{32,64}().
3) Add comments explaining the current state of optimizations in compilers we care about.
4) Change C-style includes, like <stdint.h>, to C++ style, like <cstdint>.
5) memcpy -> std::memcpy.

The optimization comments are based on https://godbolt.org/z/RdIqS1. The missed optimization opportunities in clang have been reported as https://bugs.llvm.org/show_bug.cgi?id=41761

The change does not have significant impact on benchmarks. Results below.

LevelDB:    version 1.22
Date:       Mon May  6 10:42:18 2019
CPU:        72 * Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz
CPUCache:   25344 KB
Keys:       16 bytes each
Values:     100 bytes each (50 bytes after compression)
Entries:    1000000
RawSize:    110.6 MB (estimated)
FileSize:   62.9 MB (estimated)

With change
------------------------------------------------
fillseq      :       2.327 micros/op;   47.5 MB/s
fillsync     :    4185.526 micros/op;    0.0 MB/s (1000 ops)
fillrandom   :       3.662 micros/op;   30.2 MB/s
overwrite    :       4.261 micros/op;   26.0 MB/s
readrandom   :       4.239 micros/op; (1000000 of 1000000 found)
readrandom   :       3.649 micros/op; (1000000 of 1000000 found)
readseq      :       0.174 micros/op;  636.7 MB/s
readreverse  :       0.271 micros/op;  408.7 MB/s
compact      :  570495.000 micros/op;
readrandom   :       2.735 micros/op; (1000000 of 1000000 found)
readseq      :       0.118 micros/op;  937.3 MB/s
readreverse  :       0.190 micros/op;  583.7 MB/s
fill100K     :     860.164 micros/op;  110.9 MB/s (1000 ops)
crc32c       :       1.131 micros/op; 3455.2 MB/s (4K per op)
snappycomp   :       3.034 micros/op; 1287.5 MB/s (output: 55.1%)
snappyuncomp :       0.544 micros/op; 7176.0 MB/s

Baseline
------------------------------------------------
fillseq      :       2.365 micros/op;   46.8 MB/s
fillsync     :    4240.165 micros/op;    0.0 MB/s (1000 ops)
fillrandom   :       3.244 micros/op;   34.1 MB/s
overwrite    :       4.153 micros/op;   26.6 MB/s
readrandom   :       4.698 micros/op; (1000000 of 1000000 found)
readrandom   :       4.065 micros/op; (1000000 of 1000000 found)
readseq      :       0.192 micros/op;  576.3 MB/s
readreverse  :       0.286 micros/op;  386.7 MB/s
compact      :  635979.000 micros/op;
readrandom   :       3.264 micros/op; (1000000 of 1000000 found)
readseq      :       0.169 micros/op;  652.8 MB/s
readreverse  :       0.213 micros/op;  519.5 MB/s
fill100K     :    1055.367 micros/op;   90.4 MB/s (1000 ops)
crc32c       :       1.353 micros/op; 2887.3 MB/s (4K per op)
snappycomp   :       3.036 micros/op; 1286.7 MB/s (output: 55.1%)
snappyuncomp :       0.540 micros/op; 7238.6 MB/s
PiperOrigin-RevId: 246856811

Use clang-format to correct formatting to be in agreement with the [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html). Doing this simplifies the process of accepting changes. Also fixed a few warnings flagged by clang-tidy.

PiperOrigin-RevId: 246350737

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192365747

Highlights
----------
Mmap at most 1000 files on Posix to improve performance for large databases.
Support for more architectures (thanks to Alexander K.)

Building and porting
--------------------
HP/UX support (issue 126)
AtomicPointer for ia64 (issue 123)
Sparc v9 support (issue 124)
Atomic ops for powerpc
Use -fno-builtin-memcmp only when using g++
Simplify IOS build rules (issue 114)
Use CXXFLAGS instead of CFLAGS when invoking C++ compiler (issue 118)
Fix snappy shared library problem (issue 94)
Fix shared library installation path regression
Endian-ness detection tweak for FreeBSD

Bug fixes
---------
Stop ignoring FLAGS_open_files in db_bench
Make bloom test behavior agnostic to endian-ness

Performance
-----------
Limit number of mmapped files to 1000 to improve perf for large dbs
Do not delay for 1 second on shutdown path (issue 125)

Misc
----
Make InMemoryEnv return a no-op logger
C binding now has a wrapper for free (issue 117)
Add thread-safety annotations
Added an in-process lock table (issue 120)
Make RandomAccessFile and SequentialFile non-copyable

- Replace raw slice comparison with a call to user comparator.
  Added test for custom comparators.

- Fix end of namespace comments.

- Fixed bug in picking inputs for a level-0 compaction.

  When finding overlapping files, the covered range may expand
  as files are added to the input set.  We now correctly expand
  the range when this happens instead of continuing to use the
  old range.  For example, suppose L0 contains files with the
  following ranges:

      F1: a .. d
      F2:    c .. g
      F3:       f .. j

  and the initial compaction target is F3.  We used to search
  for range f..j which yielded {F2,F3}.  However we now expand
  the range as soon as another file is added.  In this case,
  when F2 is added, we expand the range to c..j and restart the
  search.  That picks up file F1 as well.

  This change fixes a bug related to deleted keys showing up
  incorrectly after a compaction as described in Issue 44.

(Sync with upstream @25072954)

* env_chromium.cc should not export symbols.
* Fix MSVC warnings.
* Removed large value support.
* Fix broken reference to documentation file

git-svn-id: https://leveldb.googlecode.com/svn/trunk@24 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@23 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@21 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@20 62dab493-f737-651d-591e-8d6aee1b9529

git-svn-id: https://leveldb.googlecode.com/svn/trunk@2 62dab493-f737-651d-591e-8d6aee1b9529