From 8770cc71e9882414046f5f11b4e57a303381327f Mon Sep 17 00:00:00 2001
From: Jason Nelson <jason@carbonmade.com>
Date: Thu, 22 Mar 2018 17:52:46 -0700
Subject: [PATCH] Update Checksum algorithms to use Spans

---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  |  2 +-
 src/ImageSharp/Formats/Png/Zlib/Adler32.cs    | 25 ++++---------------
 src/ImageSharp/Formats/Png/Zlib/Crc32.cs      | 23 +++--------------
 src/ImageSharp/Formats/Png/Zlib/IChecksum.cs  | 22 ++++------------
 .../Formats/Png/Zlib/ZlibDeflateStream.cs     |  2 +-
 5 files changed, 15 insertions(+), 59 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 26a8b48df3..c3750eb09f 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -677,7 +677,7 @@ namespace SixLabors.ImageSharp.Formats.Png
 
             if (data != null && length > 0)
             {
-                this.crc.Update(data, offset, length);
+                this.crc.Update(new ReadOnlySpan<byte>(data, offset, length));
             }
 
             WriteInteger(stream, (uint)this.crc.Value);
diff --git a/src/ImageSharp/Formats/Png/Zlib/Adler32.cs b/src/ImageSharp/Formats/Png/Zlib/Adler32.cs
index 1cce90c0b7..9c4e9e4b99 100644
--- a/src/ImageSharp/Formats/Png/Zlib/Adler32.cs
+++ b/src/ImageSharp/Formats/Png/Zlib/Adler32.cs
@@ -113,30 +113,15 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Update(byte[] buffer)
+        public void Update(ReadOnlySpan<byte> data)
         {
-            if (buffer == null)
-            {
-                throw new ArgumentNullException(nameof(buffer));
-            }
-
-            this.Update(buffer, 0, buffer.Length);
-        }
-
-        /// <inheritdoc/>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Update(byte[] buffer, int offset, int count)
-        {
-            DebugGuard.NotNull(buffer, nameof(buffer));
-            DebugGuard.MustBeGreaterThanOrEqualTo(offset, 0, nameof(offset));
-            DebugGuard.MustBeGreaterThanOrEqualTo(count, 0, nameof(count));
-            DebugGuard.MustBeLessThan(offset, buffer.Length, nameof(offset));
-            DebugGuard.MustBeLessThanOrEqualTo(offset + count, buffer.Length, nameof(count));
-
             // (By Per Bothner)
             uint s1 = this.checksum & 0xFFFF;
             uint s2 = this.checksum >> 16;
 
+            int count = data.Length;
+            int offset = 0;
+
             while (count > 0)
             {
                 // We can defer the modulo operation:
@@ -151,7 +136,7 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
                 count -= n;
                 while (--n >= 0)
                 {
-                    s1 = s1 + (uint)(buffer[offset++] & 0xff);
+                    s1 = s1 + (uint)(data[offset++] & 0xff);
                     s2 = s2 + s1;
                 }
 
diff --git a/src/ImageSharp/Formats/Png/Zlib/Crc32.cs b/src/ImageSharp/Formats/Png/Zlib/Crc32.cs
index bd686f2b9f..d1588c384f 100644
--- a/src/ImageSharp/Formats/Png/Zlib/Crc32.cs
+++ b/src/ImageSharp/Formats/Png/Zlib/Crc32.cs
@@ -137,30 +137,13 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
 
         /// <inheritdoc/>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Update(byte[] buffer)
+        public void Update(ReadOnlySpan<byte> data)
         {
-            if (buffer == null)
-            {
-                throw new ArgumentNullException(nameof(buffer));
-            }
-
-            this.Update(buffer, 0, buffer.Length);
-        }
-
-        /// <inheritdoc/>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Update(byte[] buffer, int offset, int count)
-        {
-            DebugGuard.NotNull(buffer, nameof(buffer));
-            DebugGuard.MustBeGreaterThanOrEqualTo(count, 0, nameof(count));
-            DebugGuard.MustBeGreaterThanOrEqualTo(offset, 0, nameof(offset));
-            DebugGuard.MustBeLessThanOrEqualTo(offset + count, buffer.Length, nameof(count));
-
             this.crc ^= CrcSeed;
 
-            while (--count >= 0)
+            for (int i = 0; i < data.Length; i++)
             {
-                this.crc = CrcTable[(this.crc ^ buffer[offset++]) & 0xFF] ^ (this.crc >> 8);
+                this.crc = CrcTable[(this.crc ^ data[i]) & 0xFF] ^ (this.crc >> 8);
             }
 
             this.crc ^= CrcSeed;
diff --git a/src/ImageSharp/Formats/Png/Zlib/IChecksum.cs b/src/ImageSharp/Formats/Png/Zlib/IChecksum.cs
index 9d84258cae..a2a57332b1 100644
--- a/src/ImageSharp/Formats/Png/Zlib/IChecksum.cs
+++ b/src/ImageSharp/Formats/Png/Zlib/IChecksum.cs
@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
+
 namespace SixLabors.ImageSharp.Formats.Png.Zlib
 {
     /// <summary>
@@ -34,25 +36,11 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
         void Update(int value);
 
         /// <summary>
-        /// Updates the data checksum with the bytes taken from the array.
+        /// Updates the data checksum with the bytes taken from the span.
         /// </summary>
-        /// <param name="buffer">
+        /// <param name="data">
         /// buffer an array of bytes
         /// </param>
-        void Update(byte[] buffer);
-
-        /// <summary>
-        /// Adds the byte array to the data checksum.
-        /// </summary>
-        /// <param name = "buffer">
-        /// The buffer which contains the data
-        /// </param>
-        /// <param name = "offset">
-        /// The offset in the buffer where the data starts
-        /// </param>
-        /// <param name = "count">
-        /// the number of data bytes to add.
-        /// </param>
-        void Update(byte[] buffer, int offset, int count);
+        void Update(ReadOnlySpan<byte> data);
     }
 }
diff --git a/src/ImageSharp/Formats/Png/Zlib/ZlibDeflateStream.cs b/src/ImageSharp/Formats/Png/Zlib/ZlibDeflateStream.cs
index dd20886ff7..51e6b4859e 100644
--- a/src/ImageSharp/Formats/Png/Zlib/ZlibDeflateStream.cs
+++ b/src/ImageSharp/Formats/Png/Zlib/ZlibDeflateStream.cs
@@ -163,7 +163,7 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
         public override void Write(byte[] buffer, int offset, int count)
         {
             this.deflateStream.Write(buffer, offset, count);
-            this.adler32.Update(buffer, offset, count);
+            this.adler32.Update(new ReadOnlySpan<byte>(buffer, offset, count));
         }
 
         /// <inheritdoc/>