Improve the performance of the update method

Author: koher

Sources/EasyImagy/HigherOrderFunctions.swift

@@ -1421,8 +1421,12 @@ extension Image {
     @_specialize(exported: true, where Pixel == Double)
     @_specialize(exported: true, where Pixel == Bool)
     public mutating func update(_ body: (inout Pixel) throws -> ()) rethrows {
-        for i in pixels.indices {
-            try body(&pixels[i])
+        pixels.withUnsafeMutableBufferPointer {
+            var pointer = $0.baseAddress!
+            for _ in 0..<count {
+                try body(&pointer.pointee)
+                pointer += 1
+            }
         }
     }
 }

Tests/EasyImagyTests/HigherOrderFunctionsTests.swift

@@ -91,6 +91,13 @@ class HigherOrderFunctionsTests : XCTestCase {
         }
     }
 
+    func testUpdatePerformance() {
+        var image = Image<Int>(width: 1024, height: 1024, pixels: 1...(1024 * 1024))
+        measure {
+            image.update { $0 += 1 }
+        }
+    }
+    
     static var allTests = [
         ("testMap", testMap),
         ("testUpdate", testUpdate),