"\xff" is parsed as weird bytes

[Hecate2]

nccs 3.6.0

        public static ByteString EncodeIntegerFixedLength(BigInteger i, BigInteger fixedLength)
        {
            ByteString data = (ByteString)i;
            BigInteger lengthToComplement = fixedLength - data.Length;
            if (lengthToComplement < 0)
                throw new ArgumentException("Too long value " + data);
            if (lengthToComplement > 0)
            {
                ByteString suffix = "";
                for (; lengthToComplement > 0; --lengthToComplement)
                    suffix += i >= 0 ? "\x00" : "\xff";  // watch this
                data += suffix;
            }
            return data;
        }

# Code RelationalDB.cs line 332: "suffix += i >= 0 ? "\x00" : "\xff";"
1187 LDLOC2
1188 LDARG0
1189 PUSH0
1190 GE
1191 JMPIFNOT 07 # pos: 1198 (offset: 7)
1193 PUSHDATA1 00 # as text: "\x00"
1196 JMP 06 # pos: 1202 (offset: 6)
1198 PUSHDATA1 C3-BF # as text: "?"     # IT PUSHES "?" instead of "\xff"
1202 CAT
1203 CONVERT 28 # ByteString type
1205 DUP
1206 STLOC2
1207 DROP

invokefunction('encodeIntegerFixedLength', [-1, 4])
b'\xff\xc3\xbf\xc3\xbf\xc3\xbf'
# expected b'\xff\xff\xff\xff'

And it is not the ternary operator [condition]:[expr1]?[expr2] that lead to the problem. I used if else, and the result is still b'\xff\xc3\xbf\xc3\xbf\xc3\xbf':

        public static ByteString EncodeIntegerFixedLength(BigInteger i, BigInteger fixedLength)
        {
            ByteString data = (ByteString)i;
            BigInteger lengthToComplement = fixedLength - data.Length;
            if (lengthToComplement < 0)
                throw new ArgumentException("Too long value " + data);
            if (lengthToComplement > 0)
            {
                ByteString suffix = "";
                for (; lengthToComplement > 0; --lengthToComplement)
                {
                    if (i >= 0)
                        suffix += "\x00";
                    else
                        suffix += "\xff";
                }
                data += suffix;
            }
            return data;
        }

# Code RelationalDB.cs line 336: "suffix += "\xff";"
1204 LDLOC2
1205 PUSHDATA1 C3-BF # as text: "?"
1209 CAT
1210 CONVERT 28 # ByteString type
1212 DUP
1213 STLOC2
1214 DROP

[Hecate2]

It is a duplicate of #794 , because at

neo-devpack-dotnet/src/Neo.Compiler.CSharp/MethodConvert.cs

Line 1410 in 8fdc94d

Optional<object?> constant = model.GetConstantValue(syntax);

for syntax == StringLiteralExpression "\xff", the resulting constant.Value is "ÿ". And at

neo-devpack-dotnet/src/Neo.Compiler.CSharp/MethodConvert.cs

Line 3604 in 8fdc94d

return Push(Utility.StrictUTF8.GetBytes(s));

Utility.StrictUTF8.GetBytes(s) returns "?" ("\xc2\xb6").
The workaround is

suffix += i >= 0 ? new byte[] { 0x00 } : new byte[] { 0xff };