private bool DecodeVLQPrefix(int idx, out Substitution result)
{
result = null;
if (idx <= 0 || (Bytes[idx - 1] & 0x80) != 0)
{
return(false);
}
int decodedLength = 0;
for (int i = 1; i <= 5; i++)
{
int lengthLowIdx = idx - i;
if (lengthLowIdx < 0)
{
break;
}
int b = Bytes[lengthLowIdx];
bool metLengthFinalByte = i != 1 && (b & 0x80) == 0;
if (metLengthFinalByte)
{
break;
}
decodedLength = (decodedLength << 7) | (b & 0x7F);
if (decodedLength > Span.Length)
{
break;
}
if (decodedLength < LeastLength)
{
continue;
}
string newValue = decodedLength == Span.Length ? Span.Value
: Encoding.UTF8.GetString(Bytes, lengthLowIdx, decodedLength);
result = new VLQPrefixedSubst()
{
Offset = lengthLowIdx,
Length = decodedLength,
Value = newValue,
};
return(true);
}
return(false);
}
public bool ScanPrefix(Substitution span, out Substitution result)
{
Span = span;
LeastLength = Math.Max(2, Span.Length - 10);
result = null;
// Reference document: MS-NRBF
int scanEnd = Span.Offset + Math.Min(10, Span.Length);
for (int idx = Span.Offset; idx < scanEnd; idx++)
{
if (DecodeIntPrefix(idx, out result))
{
return(true);
}
if (DecodeVLQPrefix(idx, out result))
{
return(true);
}
}
return(false);
}
