TheXamlGuy
61 lines
1.8 KiB
C#
61 lines
1.8 KiB
C#
namespace Gma.QrCodeNet.Encoding.EncodingRegion;
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internal static class BCHCalculator
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{
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/// <summary>
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/// Calculate int length by search for Most significant bit
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/// </summary>
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/// <param name="num">Input Number</param>
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/// <returns>Most significant bit</returns>
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internal static int PosMSB(int num) => num == 0 ? 0 : BinarySearchPos(num, 0, 32) + 1;
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/// <summary>
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/// Search for right side bit of Most significant bit
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/// </summary>
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/// <param name="num">Input number</param>
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/// <param name="lowBoundary">Lower boundary. At start should be 0</param>
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/// <param name="highBoundary">Higher boundary. At start should be 32</param>
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/// <returns>Most significant bit - 1</returns>
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private static int BinarySearchPos(int num, int lowBoundary, int highBoundary)
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{
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int mid = (lowBoundary + highBoundary) / 2;
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int shiftResult = num >> mid;
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if (shiftResult == 1)
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{
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return mid;
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}
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else if (shiftResult < 1)
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{
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return BinarySearchPos(num, lowBoundary, mid);
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}
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else
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{
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return BinarySearchPos(num, mid, highBoundary);
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}
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}
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/// <summary>
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/// With input number and polynomial number. Method will calculate BCH value and return
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/// </summary>
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/// <param name="num">Input number</param>
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/// <param name="poly">Polynomial number</param>
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/// <returns>BCH value</returns>
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internal static int CalculateBCH(int num, int poly)
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{
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int polyMSB = PosMSB(poly);
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// num's length will be old length + new length - 1.
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// Once divide poly number. BCH number will be one length short than Poly number's length.
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num <<= (polyMSB - 1);
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int numMSB = PosMSB(num);
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while (PosMSB(num) >= polyMSB)
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{
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// left shift Poly number to same level as num. Then xor.
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// Remove most significant bits of num.
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num ^= poly << (numMSB - polyMSB);
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numMSB = PosMSB(num);
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}
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return num;
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}
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}
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