feat: add truncate_utils.h

Author: zhjwpku

src/iceberg/transform_function.cc

@@ -27,6 +27,7 @@
 
 #include "iceberg/type.h"
 #include "iceberg/util/murmurhash3_internal.h"
+#include "iceberg/util/truncate_utils.h"
 
 namespace iceberg {
 
@@ -57,7 +58,7 @@ Result<Literal> BucketTransform::Transform(const Literal& literal) {
         "Cannot apply bucket transform to literal with value {} of type {}",
         literal.ToString(), source_type()->ToString());
   }
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     return Literal::Null(iceberg::int32());
   }
 
@@ -135,19 +136,19 @@ Result<Literal> TruncateTransform::Transform(const Literal& literal) {
         "Cannot apply truncate transform to literal with value {} of type {}",
         literal.ToString(), source_type()->ToString());
   }
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     // Return null as is
     return literal;
   }
 
   switch (source_type()->type_id()) {
     case TypeId::kInt: {
       auto value = std::get<int32_t>(literal.value());
-      return Literal::Int(value - (((value % width_) + width_) % width_));
+      return Literal::Int(TruncateUtils::TruncateInt(value, width_));
     }
     case TypeId::kLong: {
       auto value = std::get<int64_t>(literal.value());
-      return Literal::Long(value - (((value % width_) + width_) % width_));
+      return Literal::Long(TruncateUtils::TruncateLong(value, width_));
     }
     case TypeId::kDecimal: {
       // TODO(zhjwpku): Handle decimal truncation logic here
@@ -156,26 +157,11 @@ Result<Literal> TruncateTransform::Transform(const Literal& literal) {
     case TypeId::kString: {
       // Strings are truncated to a valid UTF-8 string with no more than L code points.
       auto value = std::get<std::string>(literal.value());
-      size_t code_point_count = 0;
-      size_t safe_point = 0;
-
-      for (size_t i = 0; i < value.size(); ++i) {
-        // Start of a new UTF-8 code point
-        if ((value[i] & 0xC0) != 0x80) {
-          code_point_count++;
-          if (code_point_count > static_cast<size_t>(width_)) {
-            safe_point = i;
-            break;
-          }
-        }
-      }
-
-      if (safe_point != 0) {
-        value.resize(safe_point);  // Resize the string to the safe point
-      }
-      return Literal::String(value);
+      return Literal::String(TruncateUtils::TruncateUTF8(std::move(value), width_));
     }
     case TypeId::kBinary: {
+      /// In contrast to strings, binary values do not have an assumed encoding and are
+      /// truncated to L bytes.
       auto value = std::get<std::vector<uint8_t>>(literal.value());
       if (value.size() > static_cast<size_t>(width_)) {
         value.resize(width_);
@@ -221,7 +207,7 @@ Result<Literal> YearTransform::Transform(const Literal& literal) {
         "Cannot apply year transform to literal with value {} of type {}",
         literal.ToString(), source_type()->ToString());
   }
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     return Literal::Null(iceberg::int32());
   }
 
@@ -274,7 +260,7 @@ Result<Literal> MonthTransform::Transform(const Literal& literal) {
         "Cannot apply month transform to literal with value {} of type {}",
         literal.ToString(), source_type()->ToString());
   }
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     return Literal::Null(iceberg::int32());
   }
 
@@ -339,7 +325,7 @@ Result<Literal> DayTransform::Transform(const Literal& literal) {
         "Cannot apply day transform to literal with value {} of type {}",
         literal.ToString(), source_type()->ToString());
   }
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     return Literal::Null(iceberg::int32());
   }
 
@@ -394,7 +380,7 @@ Result<Literal> HourTransform::Transform(const Literal& literal) {
         literal.ToString(), source_type()->ToString());
   }
 
-  if (literal.IsNull()) {
+  if (literal.IsNull()) [[unlikely]] {
     return Literal::Null(int32());
   }
 

src/iceberg/util/truncate_utils.h

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <string>
+
+#include "iceberg/iceberg_export.h"
+
+namespace iceberg {
+
+ICEBERG_EXPORT class TruncateUtils {
+ public:
+  static std::string TruncateUTF8(std::string&& source, size_t L) {
+    size_t code_point_count = 0;
+    size_t safe_point = 0;
+
+    for (size_t i = 0; i < source.size(); ++i) {
+      // Start of a new UTF-8 code point
+      if ((source[i] & 0xC0) != 0x80) {
+        code_point_count++;
+        if (code_point_count > L) {
+          safe_point = i;
+          break;
+        }
+      }
+    }
+
+    if (safe_point != 0) {
+      // Resize the string to the safe point
+      source.resize(safe_point);
+    }
+
+    return std::move(source);
+  }
+};
+
+}  // namespace iceberg