private static int DetermineCerBitStringTotalLength(Asn1Tag tag, int contentLength)
{
const int MaxCERSegmentSize = AsnReader.MaxCERSegmentSize;
// Every segment has an "unused bit count" byte.
const int MaxCERContentSize = MaxCERSegmentSize - 1;
Debug.Assert(contentLength > MaxCERContentSize);
int fullSegments = Math.DivRem(contentLength, MaxCERContentSize, out int lastContentSize);
// The tag size is 1 byte.
// The length will always be encoded as 82 03 E8 (3 bytes)
// And 1000 content octets (by T-REC-X.690-201508 sec 9.2)
const int FullSegmentEncodedSize = 1004;
Debug.Assert(
1 + 1 + MaxCERSegmentSize + GetEncodedLengthSubsequentByteCount(MaxCERSegmentSize) == FullSegmentEncodedSize);
int remainingEncodedSize;
if (lastContentSize == 0)
{
remainingEncodedSize = 0;
}
else
{
// One byte of tag, minimum one byte of length, and one byte of unused bit count.
remainingEncodedSize = 3 + lastContentSize + GetEncodedLengthSubsequentByteCount(lastContentSize);
}
// Reduce the number of copies by pre-calculating the size.
// +2 for End-Of-Contents
// +1 for 0x80 indefinite length
// +tag length
return((fullSegments * FullSegmentEncodedSize) + remainingEncodedSize + 3 + tag.CalculateEncodedSize());
}