improve perf and readbility

Author: wgtmac

src/iceberg/util/transform_util.cc

@@ -25,9 +25,9 @@
 namespace iceberg {
 
 namespace {
-const auto kEpochDate = std::chrono::year{1970} / std::chrono::January / 1;
-constexpr int64_t kMicrosPerMillis = 1000;
-constexpr int64_t kMicrosPerSecond = 1000000;
+constexpr auto kEpochDate = std::chrono::year{1970} / std::chrono::January / 1;
+constexpr int64_t kMicrosPerMillis = 1'000;
+constexpr int64_t kMicrosPerSecond = 1'000'000;
 }  // namespace
 
 std::string TransformUtil::HumanYear(int32_t year_ordinal) {
@@ -93,40 +93,49 @@ std::string TransformUtil::HumanTimestampWithZone(int64_t timestamp_micros) {
 }
 
 std::string TransformUtil::Base64Encode(std::string_view str_to_encode) {
-  static const std::string base64_chars =
+  static constexpr std::string_view kBase64Chars =
       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
   int32_t i = 0;
   int32_t j = 0;
-  std::array<char, 3> char_array_3;
-  std::array<char, 4> char_array_4;
+  std::array<unsigned char, 3> char_array_3;
+  std::array<unsigned char, 4> char_array_4;
 
   std::string encoded;
   encoded.reserve((str_to_encode.size() + 2) * 4 / 3);
 
-  for (char byte : str_to_encode) {
+  for (unsigned char byte : str_to_encode) {
     char_array_3[i++] = byte;
     if (i == 3) {
       char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
       char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
       char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
       char_array_4[3] = char_array_3[2] & 0x3f;
 
-      for (j = 0; j < 4; j++) encoded += base64_chars[char_array_4[j]];
+      for (j = 0; j < 4; j++) {
+        encoded += kBase64Chars[char_array_4[j]];
+      }
+
       i = 0;
     }
   }
 
   if (i) {
-    for (j = i; j < 3; j++) char_array_3[j] = '\0';
+    for (j = i; j < 3; j++) {
+      char_array_3[j] = '\0';
+    }
 
     char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
     char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
     char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
     char_array_4[3] = char_array_3[2] & 0x3f;
 
-    for (j = 0; j < i + 1; j++) encoded += base64_chars[char_array_4[j]];
+    for (j = 0; j < i + 1; j++) {
+      encoded += kBase64Chars[char_array_4[j]];
+    }
 
-    while (i++ < 3) encoded += '=';
+    while (i++ < 3) {
+      encoded += '=';
+    }
   }
 
   return encoded;