System.Net.WebUtility.GetNextUnicodeScalarValueFromUtf16Surrogate C# (CSharp) Method

        private static unsafe int GetNextUnicodeScalarValueFromUtf16Surrogate(ref char* pch, ref int charsRemaining)
        {
            // invariants
            Debug.Assert(charsRemaining >= 1);
            Debug.Assert(Char.IsSurrogate(*pch));

            if (charsRemaining <= 1)
            {
                // not enough characters remaining to resurrect the original scalar value
                return UnicodeReplacementChar;
            }

            char leadingSurrogate = pch[0];
            char trailingSurrogate = pch[1];

            if (Char.IsSurrogatePair(leadingSurrogate, trailingSurrogate))
            {
                // we're going to consume an extra char
                pch++;
                charsRemaining--;

                // below code is from Char.ConvertToUtf32, but without the checks (since we just performed them)
                return (((leadingSurrogate - HIGH_SURROGATE_START) * 0x400) + (trailingSurrogate - LOW_SURROGATE_START) + UNICODE_PLANE01_START);
            }
            else
            {
                // unmatched surrogate
                return UnicodeReplacementChar;
            }
        }