[SPARK-52373] Add CRC32 struct

### What changes were proposed in this pull request?

This PR aims to add `CRC32` struct.

### Why are the changes needed?

Apache Spark Connect requires `CRC32` checksum to implement APIs like `addArtifacts`.

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

Generated-by: `Gemini 2.5 Flash`. Ask to write ASF-licensed CRC32 Swift code.
- `CRC32.swift`

I verified it manually and wrote test suite, `CRC32Tests.swift`.

Closes #191 from dongjoon-hyun/SPARK-52373.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Sources/SparkConnect/CRC32.swift

@@ -0,0 +1,81 @@
+//
+// 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.
+
+import Foundation
+
+public struct CRC32 {
+
+  /// Pre-computed CRC32 table
+  private static let crcTable: [UInt32] = {
+    var table = [UInt32](repeating: 0, count: 256)
+    let polynomial: UInt32 = 0xEDB8_8320  // IEEE 802.3 polynomial
+
+    for i in 0..<256 {
+      var c = UInt32(i)
+      for _ in 0..<8 {
+        if (c & 1) == 1 {
+          c = polynomial ^ (c >> 1)
+        } else {
+          c = c >> 1
+        }
+      }
+      table[i] = c
+    }
+    return table
+  }()
+
+  /// Calculates the CRC32 checksum for the given Data.
+  ///
+  /// - Parameter data: The Data object for which to calculate the checksum.
+  /// - Returns: The calculated CRC32 checksum as a UInt32.
+  public static func checksum(data: Data) -> UInt32 {
+    var crc: UInt32 = 0xFFFF_FFFF
+
+    data.withUnsafeBytes { (pointer: UnsafeRawBufferPointer) in
+      for byte in pointer.bindMemory(to: UInt8.self) {
+        crc = (crc >> 8) ^ crcTable[Int((crc ^ UInt32(byte)) & 0xFF)]
+      }
+    }
+    return ~crc
+  }
+
+  /// Calculates the CRC32 checksum for the given String.
+  ///
+  /// - Parameter string: The String object for which to calculate the checksum.
+  /// - Parameter encoding: The encoding to use when converting the string to Data (defaults to .utf8).
+  /// - Returns: The calculated CRC32 checksum as a UInt32. Returns nil if the string cannot be converted to Data.
+  public static func checksum(string: String, encoding: String.Encoding = .utf8) -> UInt32? {
+    guard let data = string.data(using: encoding) else {
+      return nil
+    }
+    return checksum(data: data)
+  }
+
+  /// Calculates the CRC32 checksum for the given array of bytes.
+  ///
+  /// - Parameter bytes: The [UInt8] array for which to calculate the checksum.
+  /// - Returns: The calculated CRC32 checksum as a UInt32.
+  public static func checksum(bytes: [UInt8]) -> UInt32 {
+    var crc: UInt32 = 0xFFFF_FFFF
+
+    for byte in bytes {
+      crc = (crc >> 8) ^ crcTable[Int((crc ^ UInt32(byte)) & 0xFF)]
+    }
+    return ~crc
+  }
+}

Tests/SparkConnectTests/CRC32Tests.swift

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+//
+// 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.
+//
+
+import Foundation
+import SparkConnect
+import Testing
+
+struct CRC32Tests {
+  @Test
+  func testChecksumWithEmptyData() async throws {
+    #expect(CRC32.checksum(data: Data()) == 0)
+    #expect(CRC32.checksum(string: "") == 0)
+    #expect(CRC32.checksum(bytes: []) == 0)
+  }
+
+  @Test
+  func testChecksum() async throws {
+    let str = "Apache Spark Connect Client for Swift"
+    #expect(CRC32.checksum(string: str, encoding: .ascii) == 2_736_908_745)
+    #expect(CRC32.checksum(data: str.data(using: .ascii)!) == 2_736_908_745)
+    #expect(CRC32.checksum(bytes: [UInt8](str.data(using: .ascii)!)) == 2_736_908_745)
+  }
+
+  @Test
+  func testLongChecksum() async throws {
+    let str = String(repeating: "Apache Spark Connect Client for Swift", count: 1000)
+    #expect(CRC32.checksum(string: str, encoding: .ascii) == 1_985_943_888)
+    #expect(CRC32.checksum(data: str.data(using: .ascii)!) == 1_985_943_888)
+    #expect(CRC32.checksum(bytes: [UInt8](str.data(using: .ascii)!)) == 1_985_943_888)
+  }
+}