[GitHub] [arrow] avertleyb commented on a diff in pull request #13376: ARROW-16778: [C++] Fix build/unit test issues in msvc/win32

[GitBox <gi...@apache.org>]

avertleyb commented on code in PR #13376:
URL: https://github.com/apache/arrow/pull/13376#discussion_r896300314


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cpp/src/arrow/util/bit_util.h:
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@@ -67,7 +67,14 @@ static constexpr uint8_t kBytePopcount[] = {
     5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 3, 4, 4, 5, 4, 5, 5, 6,
     4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8};
 
-static inline uint64_t PopCount(uint64_t bitmap) { return ARROW_POPCOUNT64(bitmap); }
+static inline uint64_t PopCount(uint64_t bitmap) {
+#if defined(_MSC_VER) && !defined(_M_AMD64) && !defined(_M_X64) 
+  const uint32_t* p = reinterpret_cast<const uint32_t*>((void*)(&bitmap));
+  return ARROW_POPCOUNT32(*p) + ARROW_POPCOUNT32(*(p + 1));

Review Comment:
   If performance is critical, I would assume this version would just add a couple of bit operation.  But if you feel it looks cleaner I can change this.  Please let me know.
   



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