[libcxx-commits] [PATCH] D134124: [libc++] Fix wrong implementation of CityHash

[Tommy Chiang via Phabricator via libcxx-commits]

oToToT created this revision.
oToToT added reviewers: EricWF, ldionne.
Herald added a project: All.
oToToT requested review of this revision.
Herald added a project: libc++.
Herald added a reviewer: libc++.

As PR56606 stated, the current implementation of CityHash in libc++
would drop some bits unintentionally. Cast the 32bit int to the 64bit
int to avoid this happened.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134124

Files:
  libcxx/include/__functional/hash.h


Index: libcxx/include/__functional/hash.h
===================================================================
--- libcxx/include/__functional/hash.h
+++ libcxx/include/__functional/hash.h
@@ -135,7 +135,7 @@
     if (__len >= 4) {
       const uint32_t __a = __loadword<uint32_t>(__s);
       const uint32_t __b = __loadword<uint32_t>(__s + __len - 4);
-      return __hash_len_16(__len + (__a << 3), __b);
+      return __hash_len_16(__len + (static_cast<_Size>(__a) << 3), __b);
     }
     if (__len > 0) {
       const unsigned char __a = static_cast<unsigned char>(__s[0]);


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