fix build warnnings on MSVC (#6309)

Summary:
Fix build warnings on MSVC. siying
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6309

Differential Revision: D19455012

Pulled By: ltamasi

fbshipit-source-id: 940739f2c92de60e47cc2bed8dd7f921459545a9

db_stress_tool/db_stress_common.cc

@@ -62,7 +62,7 @@ void InitializeHotKeyGenerator(double alpha) {
 int64_t GetOneHotKeyID(double rand_seed, int64_t max_key) {
   int64_t low = 1, mid, high = zipf_sum_size, zipf = 0;
   while (low <= high) {
-    mid = std::floor((low + high) / 2);
+    mid = (low + high) / 2;
     if (sum_probs[mid] >= rand_seed && sum_probs[mid - 1] < rand_seed) {
       zipf = mid;
       break;
@@ -72,8 +72,7 @@ int64_t GetOneHotKeyID(double rand_seed, int64_t max_key) {
       low = mid + 1;
     }
   }
-  int64_t tmp_zipf_seed = static_cast<int64_t>(
-      std::floor(zipf * max_key / (static_cast<double>(zipf_sum_size))));
+  int64_t tmp_zipf_seed = zipf * max_key / zipf_sum_size;
   Random64 rand_local(tmp_zipf_seed);
   return rand_local.Next() % max_key;
 }

db_stress_tool/db_stress_test_base.cc

@@ -771,7 +771,7 @@ std::vector<std::string> StressTest::GetWhiteBoxKeys(ThreadState* thread,
           k[i] = static_cast<char>(cur - 1);
           break;
         } else if (i > 0) {
-          k[i] = 0xFF;
+          k[i] = 0xFFu;
         }
       }
     } else if (thread->rand.OneIn(2)) {
@@ -1550,7 +1550,7 @@ void StressTest::TestCompactRange(ThreadState* thread, int64_t rand_key,
   cro.max_subcompactions = static_cast<uint32_t>(thread->rand.Next() % 4);
 
   const Snapshot* pre_snapshot = nullptr;
-  uint32_t pre_hash;
+  uint32_t pre_hash = 0;
   if (thread->rand.OneIn(2)) {
     // Do some validation by declaring a snapshot and compare the data before
     // and after the compaction

util/filter_bench.cc

@@ -330,8 +330,8 @@ void FilterBench::Go() {
     if (FLAGS_use_plain_table_bloom) {
       info.plain_table_bloom_.reset(new PlainTableBloomV1());
       info.plain_table_bloom_->SetTotalBits(
-          &arena_, keys_to_add * FLAGS_bits_per_key, FLAGS_impl,
-          0 /*huge_page*/, nullptr /*logger*/);
+          &arena_, static_cast<uint32_t>(keys_to_add * FLAGS_bits_per_key),
+          FLAGS_impl, 0 /*huge_page*/, nullptr /*logger*/);
       for (uint32_t i = 0; i < keys_to_add; ++i) {
         uint32_t hash = GetSliceHash(kms_[0].Get(filter_id, i));
         info.plain_table_bloom_->AddHash(hash);