public static XPolynom operator +(XPolynom left, XPolynom right)
{
XPolynom @short, @long;
if (left.PolynomsCount > right.PolynomsCount)
{
@long = left; @short = right;
}
else
{
@short = left; @long = right;
}
var ret = new XPolynom(@long.PolynomsCount);
int i = 0;
for (; i < @short.PolynomsCount; i++)
{
ret[i] = @long[i] + @short[i];
}
for (; i < @long.PolynomsCount; i++)
{
ret[i] = @long[i];
}
ret.ReLength();
return(ret);
}
/// <summary>
/// 快速RS编码
/// </summary>
/// <param name="msg"></param>
/// <param name="msgIndex"></param>
/// <param name="msgLength"></param>
/// <param name="eccCount"></param>
/// <returns></returns>
public static byte[] RSEncode(byte[] msg, int msgIndex, int msgLength, int eccCount)
{
var gp = Cache <int, XPolynom> .Get(eccCount, n => {
var g = new XPolynom(FromExponent(0), FromExponent(0));
for (int i = 1; i < n; i++)
{
g *= new XPolynom(FromExponent(i), FromExponent(0));
}
return(g);
});
byte[] rem = new byte[eccCount];
Array.Copy(msg, msgIndex, rem, 0, Math.Min(msgLength, eccCount));
for (int i = 0; i < msgLength; i++)
{
var div = FromPolynom(rem[0]);
for (int j = 1; j < eccCount; j++)
{
rem[j - 1] = (byte)(FromPolynom(rem[j]) + gp[eccCount - j] * div).Polynom;
}
if (i + eccCount < msgLength)
{
rem[eccCount - 1] = (byte)(FromPolynom(msg[msgIndex + i + eccCount]) + gp[0] * div).Polynom;
}
else
{
rem[eccCount - 1] = (byte)(gp[0] * div).Polynom;
}
}
return(rem);
}
public XPolynom Clone()
{
var ret = new XPolynom(PolynomsCount);
Array.Copy(polynoms, ret.polynoms, PolynomsCount);
return(ret);
}
public static XPolynom FromXPow(int xExponent)
{
var ret = new XPolynom(xExponent + 1);
ret[xExponent] = FromExponent(0);
return(ret);
}
public static XPolynom operator *(XPolynom left, GF right)
{
var ret = new XPolynom(left.PolynomsCount);
for (int i = 0; i < left.PolynomsCount; i++)
{
ret[i] = left[i] * right;
}
ret.ReLength();
return(ret);
}
public XPolynom MulXPow(int xExponent)
{
if (xExponent == 0)
{
return(this);
}
var ret = new XPolynom(PolynomsCount + xExponent);
polynoms.CopyTo(ret.polynoms, xExponent);
return(ret);
}
public static XPolynom operator *(XPolynom left, XPolynom right)
{
var ret = new XPolynom(left.PolynomsCount + right.PolynomsCount - 1);
for (int i = 0; i < left.PolynomsCount; i++)
{
for (int j = 0; j < right.PolynomsCount; j++)
{
ret[i + j] += left[i] * right[j];
}
}
return(ret);
}
public XPolynom DivMod(XPolynom right, out XPolynom rem)
{
var divVal = new XPolynom(0);
var remVal = this;
var rightHead = right[right.PolynomsCount - 1];
while (true)
{
var xExponent = remVal.PolynomsCount - right.PolynomsCount;
if (xExponent < 0)
{
break;
}
var alphaDiv = remVal[remVal.PolynomsCount - 1] / rightHead;
divVal += new XPolynom(alphaDiv).MulXPow(xExponent);
remVal += right.MulXPow(xExponent) * alphaDiv;
}
rem = remVal;
return(divVal);
}
public static void RSEncode(ReadOnlySpan <byte> msg, Span <byte> ecc)
{
int eccCount = ecc.Length;
var gp = Cache <int, XPolynom> .Get(eccCount, n => {
var g = new XPolynom(One, One);
for (int i = 1; i < n; i++)
{
g *= new XPolynom(FromExponent(i), One);
}
return(g);
});
if (msg.Length > ecc.Length)
{
msg.Slice(0, ecc.Length).CopyTo(ecc);
}
else
{
msg.CopyTo(ecc);
ecc.Slice(msg.Length).Fill(0);
}
for (int i = 0; i < msg.Length; i++)
{
var div = FromPolynom(ecc[0]);
for (int j = 1; j < eccCount; j++)
{
ecc[j - 1] = (FromPolynom(ecc[j]) + gp[eccCount - j] * div).Polynom;
}
if (i + eccCount < msg.Length)
{
ecc[eccCount - 1] = (FromPolynom(msg[i + eccCount]) + gp[0] * div).Polynom;
}
else
{
ecc[eccCount - 1] = (gp[0] * div).Polynom;
}
}
}
