use std::hash instead of hashing byte by byte

This patch uses libcxx's string_view hashing.  The performance is better than the
current implementation, and almost the same as for the hashing implementation amended
by the patch in https://android-review.googlesource.com/404742

The following experiments were conducted on a HiKey aarch64 A53.

No changes:
$ adb push out/target/product/hikey/data/benchmarktest64/ziparchive-benchmarks /data
$ adb shell /data/ziparchive-benchmarks --benchmark_repetitions=5
-----------------------------------------------------------------
Benchmark                          Time           CPU Iterations
-----------------------------------------------------------------
FindEntry_no_match          82279629 ns   81759676 ns          9
FindEntry_no_match          81648056 ns   81627431 ns          9
FindEntry_no_match          81384074 ns   81369057 ns          9
FindEntry_no_match          89618889 ns   82437755 ns          9
FindEntry_no_match          81811389 ns   81785261 ns          9
FindEntry_no_match_mean     83348407 ns   81795836 ns          9
FindEntry_no_match_stddev    3520421 ns     394962 ns          0
Iterate_all_files          137622000 ns  137589032 ns          5
Iterate_all_files          139666333 ns  138409469 ns          5
Iterate_all_files          150070000 ns  140883697 ns          5
Iterate_all_files          138600667 ns  138540646 ns          5
Iterate_all_files          137599833 ns  137567438 ns          5
Iterate_all_files_mean     140711767 ns  138598056 ns          5
Iterate_all_files_stddev     5299929 ns    1354928 ns          0

$ cd system/core/libziparchive
$ git fetch https://android.googlesource.com/platform/system/core refs/changes/42/404742/7 && git cherry-pick FETCH_HEAD
$ mma
$ cd -
$ adb push out/target/product/hikey/data/benchmarktest64/ziparchive-benchmarks /data
$ adb shell /data/ziparchive-benchmarks --benchmark_repetitions=5
-----------------------------------------------------------------
Benchmark                          Time           CPU Iterations
-----------------------------------------------------------------
FindEntry_no_match          53302756 ns   53291178 ns         13
FindEntry_no_match          54314487 ns   54272272 ns         13
FindEntry_no_match          53866923 ns   53851178 ns         13
FindEntry_no_match          53324423 ns   53317296 ns         13
FindEntry_no_match          53289231 ns   53289159 ns         13
FindEntry_no_match_mean     53619564 ns   53604216 ns         13
FindEntry_no_match_stddev     458449 ns     443527 ns          0
Iterate_all_files          128211111 ns  112254783 ns          6
Iterate_all_files          110695000 ns  110677726 ns          6
Iterate_all_files          109351250 ns  109350998 ns          6
Iterate_all_files          109367500 ns  109367796 ns          6
Iterate_all_files          110872222 ns  110591407 ns          6
Iterate_all_files_mean     113699417 ns  110448542 ns          6
Iterate_all_files_stddev     8143723 ns    1194577 ns          0

$ cd system/core/libziparchive
$ git checkout HEAD~
$ git am 0001-use-std-hash.patch
$ mma
$ cd -
$ adb push out/target/product/hikey/data/benchmarktest64/ziparchive-benchmarks /data
$ adb shell /data/ziparchive-benchmarks --benchmark_repetitions=5
-----------------------------------------------------------------
Benchmark                          Time           CPU Iterations
-----------------------------------------------------------------
FindEntry_no_match          55339872 ns   55195112 ns         13
FindEntry_no_match          56232628 ns   56069924 ns         13
FindEntry_no_match          55694103 ns   55255946 ns         13
FindEntry_no_match          55275064 ns   55120136 ns         13
FindEntry_no_match          54971987 ns   54944411 ns         13
FindEntry_no_match_mean     55502731 ns   55317106 ns         13
FindEntry_no_match_stddev     482032 ns     436766 ns          0
Iterate_all_files          114618611 ns  114487804 ns          6
Iterate_all_files          112552917 ns  112229801 ns          6
Iterate_all_files          111288750 ns  111255044 ns          6
Iterate_all_files          111291528 ns  111259045 ns          6
Iterate_all_files          114347222 ns  113677119 ns          6
Iterate_all_files_mean     112819806 ns  112581763 ns          6
Iterate_all_files_stddev     1606214 ns    1454858 ns          0

Change-Id: I1e3413d331bcb460ca38bc2c87e23f89b456cd2f

1 files changed, 6 insertions, 0 deletions

diff --git a/libziparchive/zip_archive.cc b/libziparchive/zip_archive.cc
index 35d0f0b6a..6da5c99bd 100644
--- a/libziparchive/zip_archive.cc
+++ b/libziparchive/zip_archive.cc
@@ -100,6 +100,11 @@ static uint32_t RoundUpPower2(uint32_t val) {
 }
 
 static uint32_t ComputeHash(const ZipString& name) {
+#if !defined(_WIN32)
+  return std::hash<std::string_view>{}(
+      std::string_view(reinterpret_cast<const char*>(name.name), name.name_length));
+#else
+  // Remove this code path once the windows compiler knows how to compile the above statement.
   uint32_t hash = 0;
   uint16_t len = name.name_length;
   const uint8_t* str = name.name;
@@ -109,6 +114,7 @@ static uint32_t ComputeHash(const ZipString& name) {
   }
 
   return hash;
+#endif
 }
 
 /*