SQInteger JSON::parseString()

in AzureSphereSquirrel/HLCore/json.cpp [232:329]
91 lines of code
17 McCabe index (conditional complexity)

SQInteger JSON::parseString(HSQUIRRELVM vm, char *jsonString, jsmntok_t tokens[], unsigned int tokenIndex)
{
    jsmntok_t *token = &tokens[tokenIndex];
    char *string = &jsonString[token->start];
    int stringLen = token->end - token->start;
    int finalStringLen = stringLen;

    for(int i = 0; i < stringLen-1; ++i)
    {
        if(string[i] == '\\')
        {
            switch(string[i+1])
            {
                case '"': case '\\': case '/':
                    string[i] = 255;
                    --finalStringLen;
                    ++i;
                    break;
                case 'b':
                    string[i] = 255;
                    string[i+1] = '\b';
                    --finalStringLen;
                    ++i;
                    break;
                case 'f':
                    string[i] = 255;
                    string[i+1] = '\f';
                    --finalStringLen;
                    ++i;
                    break;
                case 'n': 
                    string[i] = 255;
                    string[i+1] = '\n';
                    --finalStringLen;
                    ++i;
                    break;
                case 'r':
                    string[i] = 255;
                    string[i+1] = '\r';
                    --finalStringLen;
                    ++i;
                    break;
                case 't':
                    string[i] = 255;
                    string[i+1] = '\t';
                    --finalStringLen;
                    ++i;
                    break;
                case 'u':
                    unsigned int byteCode;

                    if(stringLen - i == 6)
                    {
                        byteCode = strtol(&string[i+2], nullptr, 16);
                    }
                    else if(stringLen - i > 6)
                    {
                        char tempChar = string[i+6];
                        string[i+6] = '\0';
                        byteCode = strtol(&string[i+2], nullptr, 16);
                        string[i+6] = tempChar;
                    }
                    else
                    {
                        return sq_throwerror(vm, "Unable to parse string token \\u");
                    }

                    if(byteCode >= 256)
                    {
                        return sq_throwerror(vm, "Unable to parse string token \\u, sizes above 1Byte not yet supported");
                    }

                    string[i] = 255;
                    string[i+1] = byteCode;
                    string[i+2] = 255;
                    string[i+3] = 255;
                    string[i+4] = 255;
                    string[i+5] = 255;
                    finalStringLen -= 5;
                    break;
                default: return sq_throwerror(vm, "Unable to parse string token, unknown escape sequence");;
            }
        }
    }

    for(int i = 0, u = 0; i < stringLen; ++i)
    {
        if(string[i] == 255)
        {
            continue;
        }

        string[u++] = string[i];
    }

    sq_pushstring(vm, string, finalStringLen);
    return SQ_OK;
}