Avoid length-check in pinning spans

Only where it seems profitable. E.g. not when a UnmanagedMemoryStream is constructed of that pointer.

src/ImageSharp/ColorSpaces/Companding/SRgbCompanding.cs

@@ -167,7 +167,7 @@ public static class SRgbCompanding
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static unsafe void CompandAvx2(Span<Vector4> vectors, float[] table)
     {
-        fixed (float* tablePointer = &table[0])
+        fixed (float* tablePointer = &MemoryMarshal.GetArrayDataReference(table))
         {
             var scale = Vector256.Create((float)Scale);
             Vector256<float> zero = Vector256<float>.Zero;
@@ -199,7 +199,7 @@ public static class SRgbCompanding
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static unsafe void CompandScalar(Span<Vector4> vectors, float[] table)
     {
-        fixed (float* tablePointer = &table[0])
+        fixed (float* tablePointer = &MemoryMarshal.GetArrayDataReference(table))
         {
             Vector4 zero = Vector4.Zero;
             var scale = new Vector4(Scale);

src/ImageSharp/Common/Helpers/SimdUtils.HwIntrinsics.cs

@@ -644,7 +644,7 @@ internal static partial class SimdUtils
             ReadOnlySpan<byte> source,
             Span<float> dest)
         {
-            fixed (byte* sourceBase = source)
+            fixed (byte* sourceBase = &MemoryMarshal.GetReference(source))
             {
                 if (Avx2.IsSupported)
                 {

src/ImageSharp/Compression/Zlib/Adler32.cs

@@ -387,7 +387,7 @@ internal static class Adler32
         uint s1 = adler & 0xFFFF;
         uint s2 = (adler >> 16) & 0xFFFF;
 
-        fixed (byte* bufferPtr = buffer)
+        fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
         {
             byte* localBufferPtr = bufferPtr;
             uint length = (uint)buffer.Length;

src/ImageSharp/Compression/Zlib/Crc32.cs

@@ -81,7 +81,7 @@ internal static partial class Crc32
         int chunksize = buffer.Length & ~ChunksizeMask;
         int length = chunksize;
 
-        fixed (byte* bufferPtr = buffer)
+        fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
         {
             fixed (ulong* k05PolyPtr = K05Poly)
             {
@@ -201,7 +201,7 @@ internal static partial class Crc32
     [MethodImpl(InliningOptions.HotPath | InliningOptions.ShortMethod)]
     private static unsafe uint CalculateArm(uint crc, ReadOnlySpan<byte> buffer)
     {
-        fixed (byte* bufferPtr = buffer)
+        fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
         {
             byte* localBufferPtr = bufferPtr;
             int len = buffer.Length;
@@ -248,7 +248,7 @@ internal static partial class Crc32
     [MethodImpl(InliningOptions.HotPath | InliningOptions.ShortMethod)]
     private static unsafe uint CalculateArm64(uint crc, ReadOnlySpan<byte> buffer)
     {
-        fixed (byte* bufferPtr = buffer)
+        fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
         {
             byte* localBufferPtr = bufferPtr;
             int len = buffer.Length;

src/ImageSharp/Formats/Webp/Lossless/LosslessUtils.cs

@@ -569,7 +569,7 @@ internal static unsafe class LosslessUtils
         Span<uint> pixelData,
         Span<uint> outputSpan)
     {
-        fixed (uint* inputFixed = pixelData)
+        fixed (uint* inputFixed = &MemoryMarshal.GetReference(pixelData))
         {
             fixed (uint* outputFixed = outputSpan)
             {
@@ -1474,8 +1474,7 @@ internal static unsafe class LosslessUtils
     {
         if (Sse2.IsSupported)
         {
-            Span<short> output = scratch;
-            fixed (short* p = output)
+            fixed (short* ptr = &MemoryMarshal.GetReference(scratch))
             {
                 Vector128<byte> a0 = Sse2.ConvertScalarToVector128UInt32(a).AsByte();
                 Vector128<byte> b0 = Sse2.ConvertScalarToVector128UInt32(b).AsByte();
@@ -1489,8 +1488,8 @@ internal static unsafe class LosslessUtils
                 Vector128<byte> pa = Sse2.UnpackLow(ac, Vector128<byte>.Zero); // |a - c|
                 Vector128<byte> pb = Sse2.UnpackLow(bc, Vector128<byte>.Zero); // |b - c|
                 Vector128<ushort> diff = Sse2.Subtract(pb.AsUInt16(), pa.AsUInt16());
-                Sse2.Store((ushort*)p, diff);
-                int paMinusPb = output[3] + output[2] + output[1] + output[0];
+                Sse2.Store((ushort*)ptr, diff);
+                int paMinusPb = ptr[3] + ptr[2] + ptr[1] + ptr[0];
                 return (paMinusPb <= 0) ? a : b;
             }
         }

src/ImageSharp/Formats/Webp/Lossless/PredictorEncoder.cs

@@ -353,8 +353,8 @@ internal static unsafe class PredictorEncoder
         else
         {
 #pragma warning disable SA1503 // Braces should not be omitted
-            fixed (uint* currentRow = currentRowSpan)
-            fixed (uint* upperRow = upperRowSpan)
+            fixed (uint* currentRow = &MemoryMarshal.GetReference(currentRowSpan))
+            fixed (uint* upperRow = &MemoryMarshal.GetReference(upperRowSpan))
             {
                 for (int x = xStart; x < xEnd; x++)
                 {
@@ -664,9 +664,9 @@ internal static unsafe class PredictorEncoder
         Span<short> scratch)
     {
 #pragma warning disable SA1503 // Braces should not be omitted
-        fixed (uint* current = currentSpan)
-        fixed (uint* upper = upperSpan)
-        fixed (uint* outputFixed = outputSpan)
+        fixed (uint* current = &MemoryMarshal.GetReference(currentSpan))
+        fixed (uint* upper = &MemoryMarshal.GetReference(upperSpan))
+        fixed (uint* outputFixed = &MemoryMarshal.GetReference(outputSpan))
         {
             uint* output = outputFixed;
             if (xStart == 0)

src/ImageSharp/Formats/Webp/WebpCommonUtils.cs

@@ -25,7 +25,7 @@ internal static class WebpCommonUtils
             ReadOnlySpan<byte> rowBytes = MemoryMarshal.AsBytes(row);
             int i = 0;
             int length = (row.Length * 4) - 3;
-            fixed (byte* src = rowBytes)
+            fixed (byte* src = &MemoryMarshal.GetReference(rowBytes))
             {
                 var alphaMaskVector256 = Vector256.Create(0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255);
                 Vector256<byte> all0x80Vector256 = Vector256.Create((byte)0x80).AsByte();
@@ -81,7 +81,7 @@ internal static class WebpCommonUtils
             ReadOnlySpan<byte> rowBytes = MemoryMarshal.AsBytes(row);
             int i = 0;
             int length = (row.Length * 4) - 3;
-            fixed (byte* src = rowBytes)
+            fixed (byte* src = &MemoryMarshal.GetReference(rowBytes))
             {
                 for (; i + 64 <= length; i += 64)
                 {

src/ImageSharp/Memory/Buffer2DExtensions.cs

@@ -50,7 +50,7 @@ public static class Buffer2DExtensions
 
         Span<byte> span = MemoryMarshal.AsBytes(buffer.DangerousGetSingleMemory().Span);
 
-        fixed (byte* ptr = span)
+        fixed (byte* ptr = &MemoryMarshal.GetReference(span))
         {
             byte* basePtr = ptr;
             for (int y = 0; y < buffer.Height; y++)