From bc64ce44b1bea97eda1da04ee4e98c05e1707746 Mon Sep 17 00:00:00 2001
From: Timofey Solomko <tsolomko@gmail.com>
Date: Sun, 18 Dec 2016 14:16:16 +0300
Subject: [PATCH] Added function which calculates crc32.

---
 Sources/CheckSums.swift | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 Sources/CheckSums.swift

diff --git a/Sources/CheckSums.swift b/Sources/CheckSums.swift
new file mode 100644
index 00000000..978c9eb4
--- /dev/null
+++ b/Sources/CheckSums.swift
@@ -0,0 +1,39 @@
+//
+//  CheckSums.swift
+//  SWCompression
+//
+//  Created by Timofey Solomko on 18.12.16.
+//  Copyright © 2016 tsolomko. All rights reserved.
+//
+
+import Foundation
+
+struct CheckSums {
+
+    static let crc32table: [UInt32] = {
+        var table: [UInt32] = Array(repeating: 0, count: 256)
+        let crc32poly = 0xEDB88320
+        var r = 0
+        var j = 0
+        for i in 0..<256 {
+            r = i
+            j = 8
+            while j > 0 {
+                r = r & 1 > 0 ? (r >> 1) ^ crc32poly : r >> 1
+                j -= 1
+            }
+            table[i] = UInt32(r)
+        }
+        return table
+    }()
+
+    static func crc32(_ array: [UInt8]) -> Int {
+        var crc: UInt32 = ~0
+        for i in 0..<array.count {
+            let index = (Int(crc) & 0xFF) ^ (array[i].toInt())
+            crc = CheckSums.crc32table[index] ^ (crc >> 8)
+        }
+        return Int(~crc)
+    }
+    
+}