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//------------------------------------------------------------
// Copyright (c) Microsoft Corporation. All rights reserved.
//------------------------------------------------------------
namespace System.IdentityModel
{
using System.Collections.Generic;
using System.Text;
static class Asn1IntegerConverter
{
static List<byte[]> powersOfTwo = new List<byte[]>(new byte[][] { new byte[] { 1 } });
readonly static char[] digitMap = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
public static string Asn1IntegerToDecimalString(byte[] asn1)
{
if (asn1 == null)
throw DiagnosticUtility.ExceptionUtility.ThrowHelperArgumentNull("asn1");
if (asn1.Length == 0)
throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new ArgumentOutOfRangeException("asn1", SR.GetString(SR.LengthOfArrayToConvertMustGreaterThanZero)));
List<byte> positiveDecimalDigits = new List<byte>((asn1.Length * 8) / 3);
int absoluteBitNumber = 0;
byte currentByte;
// Since X509Certificate.GetSerialNumber return the little-endian,
// the most significant is at the last byte.
for (int byteNumber = 0; byteNumber < asn1.Length - 1; byteNumber++)
{
currentByte = asn1[byteNumber];
for (int i = 0; i < 8; i++)
{
if ((currentByte & 1) == 1)
{
AddSecondDecimalToFirst(positiveDecimalDigits, TwoToThePowerOf(absoluteBitNumber));
}
absoluteBitNumber++;
currentByte >>= 1;
}
}
// Special case the most significant bit of the most significant byte as a negative value
currentByte = asn1[asn1.Length - 1];
for (int i = 0; i < 7; i++)
{
if ((currentByte & 1) == 1)
{
AddSecondDecimalToFirst(positiveDecimalDigits, TwoToThePowerOf(absoluteBitNumber));
}
absoluteBitNumber++;
currentByte >>= 1;
}
StringBuilder result = new StringBuilder(positiveDecimalDigits.Count + 1);
List<byte> resultDigits = null;
if (currentByte == 0)
{
// positive number
resultDigits = positiveDecimalDigits;
}
else
{
// negative number
List<byte> negativeDecimalDigits = new List<byte>(TwoToThePowerOf(absoluteBitNumber));
SubtractSecondDecimalFromFirst(negativeDecimalDigits, positiveDecimalDigits);
resultDigits = negativeDecimalDigits;
result.Append('-');
}
int d;
for (d = resultDigits.Count - 1; d >= 0; d--)
{
if (resultDigits[d] != 0)
break;
}
if (d < 0 && asn1.Length > 0)
{
// This is a special case where the result contains 0
result.Append(digitMap[0]);
}
else
{
while (d >= 0)
{
result.Append(digitMap[resultDigits[d--]]);
}
}
return result.ToString();
}
static byte[] TwoToThePowerOf(int n)
{
lock (powersOfTwo)
{
if (n >= powersOfTwo.Count)
{
for (int power = powersOfTwo.Count; power <= n; power++)
{
List<byte> decimalDigits = new List<byte>(powersOfTwo[power - 1]);
byte carryover = 0;
for (int i = 0; i < decimalDigits.Count; i++)
{
byte newValue = (byte)((decimalDigits[i] << 1) + carryover);
decimalDigits[i] = (byte)(newValue % 10);
carryover = (byte)(newValue / 10);
}
if (carryover > 0)
{
decimalDigits.Add(carryover);
carryover = 0;
}
powersOfTwo.Add(decimalDigits.ToArray());
}
}
return powersOfTwo[n];
}
}
static void AddSecondDecimalToFirst(List<byte> first, byte[] second)
{
byte carryover = 0;
for (int i = 0; i < second.Length || i < first.Count; i++)
{
if (i >= first.Count)
{
first.Add(0);
}
byte newValue;
if (i < second.Length)
{
newValue = (byte)(first[i] + second[i] + carryover);
}
else
{
newValue = (byte)(first[i] + carryover);
}
first[i] = (byte)(newValue % 10);
carryover = (byte)(newValue / 10);
}
if (carryover > 0)
{
first.Add(carryover);
}
}
static void SubtractSecondDecimalFromFirst(List<byte> first, List<byte> second)
{
byte borrow = 0;
for (int i = 0; i < second.Count; i++)
{
int newValue = first[i] - second[i] - borrow;
if (newValue < 0)
{
borrow = 1;
first[i] = (byte)(newValue + 10);
}
else
{
borrow = 0;
first[i] = (byte)newValue;
}
}
if (borrow > 0)
{
for (int i = second.Count; i < first.Count; i++)
{
int newValue = first[i] - borrow;
if (newValue < 0)
{
borrow = 1;
first[i] = (byte)(newValue + 10);
}
else
{
borrow = 0;
first[i] = (byte)newValue;
break;
}
}
}
DiagnosticUtility.DebugAssert(borrow == 0, "");
}
}
}
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