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Minor performance improvement in BitmapByteQRCode + clarify padding calculation #698

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Minor performance improvement in BitmapByteQRCode + clarify padding calculation #698

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348e0a9
Fix bug and a minor performance improvement in BitmapByteQRCode
KrisVandermotten Jul 12, 2026
405403a
Fix bug
KrisVandermotten Jul 12, 2026
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16 changes: 14 additions & 2 deletions QRCoder/BitmapByteQRCode.cs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,8 @@
#if NETCOREAPP2_1_OR_GREATER
using System.Buffers.Binary;
#endif
using System.Diagnostics;

using static QRCoder.QRCodeGenerator;

namespace QRCoder;
Expand Down Expand Up @@ -67,11 +72,14 @@ public byte[] GetGraphic(int pixelsPerModule, byte[] darkColorRgb, byte[] lightC
moduleLight[i + 2] = lightColorRgb[0];
}

// The size of each row must be rounded up to a multiple of 4 bytes by padding.
// Pre-calculate padding bytes
var paddingLen = sideLength % 4;
var rowByteLength = sideLength * 3;
var paddingLen = -rowByteLength & 3;
Debug.Assert(paddingLen >= 0 && paddingLen < 4 && (rowByteLength + paddingLen) % 4 == 0);

// Calculate filesize (header + pixel data + padding)
var fileSize = 54 + (3 * (sideLength * sideLength)) + (sideLength * paddingLen);
var fileSize = 54 + (rowByteLength + paddingLen) * sideLength;

// Bitmap container
byte[] bmp = new byte[fileSize];
Expand Down Expand Up @@ -142,13 +150,17 @@ public byte[] GetGraphic(int pixelsPerModule, byte[] darkColorRgb, byte[] lightC
/// <param name="destinationArray">Destination byte array that receives the bytes</param>
private static void CopyIntAs4ByteToArray(int inp, int destinationIndex, byte[] destinationArray)
{
#if NETCOREAPP2_1_OR_GREATER
BinaryPrimitives.WriteInt32LittleEndian(destinationArray.AsSpan(destinationIndex), inp);
#else
unchecked
{
destinationArray[destinationIndex + 3] = (byte)(inp >> 24);
destinationArray[destinationIndex + 2] = (byte)(inp >> 16);
destinationArray[destinationIndex + 1] = (byte)(inp >> 8);
destinationArray[destinationIndex + 0] = (byte)(inp);
}
#endif
}
}

Expand Down