STEAMID有以下类型，通过实例函数，可以进行相互转换

/**
 * Script to format SteamID type to another type.
 *
 * @param input            Input string where began read SteamID.
 * @param output        Destination string buffer.
 * @param maxlength     Maximum length of output string buffer.
 * @param type            SteamID type to format. AuthId_Steam2,  AuthId_Steam3 and AuthId_SteamID64
 *
 * @return              True when script format another SteamID. False when nothing happened.
 */

stock bool FormatSteamID(const char[] input, char[] output, int maxlength, AuthIdType type)
{
    AuthIdType input_type = AuthId_Engine; // This indicate input value as ERROR

    if(StrContains(input, "STEAM_", false) != -1)
    {
        if(strlen(input) <= 10 || input[7] != ':' || input[9] != ':')
        {
            return false;
        }

        int a = StringToInt(input[8]);
        int b = StringToInt(input[10]);

        if((a <= 0 && b <= 0) || a < 0 || b < 0)
            return false;

        input_type = AuthId_Steam2;
    }
    else if(StrContains(input, "[U:1:", false) != -1)
    {
        if(strlen(input) <= 5 || input[2] != ':' || input[4] != ':' || StringToInt(input[5]) <= 0)
        {
            return false;
        }
        
        input_type = AuthId_Steam3;
    }


    int higherbit = (1<<0)|(1<<20)|(1<<24); // 64-bit 76561197960265728 = STEAM_0:0:0
    int result[2];


    if(input_type == AuthId_Engine)
    {
        int len = strlen(input);

        if(len < 17)
            return false;
        
        for(int c = 0; c < len; c++)
        {
            if(!IsCharNumeric(input[c]))
                return false;
        }

        StringToInt64(input, result);

        if(result[0] <= 0 ||
            result[1] < higherbit)
        {
            return false;
        }
        
        input_type = AuthId_SteamID64;
    }


    switch(type)
    {
        case AuthId_Steam2:
        {
            if(input_type == AuthId_Steam2)
                return false;

            if(input_type == AuthId_Steam3)
            {
                int W = StringToInt(input[5]);
                int Y = W%2;
                int Z = (W-Y) / 2;

                Format(output, maxlength, "STEAM_0:%i:%i", Y, Z);

                return true;
            }
            else
            {
                int W = result[0];
                int Y = W%2;
                int Z = (W-Y) / 2;

                Format(output, maxlength, "STEAM_%i:%i:%i",
                                                    result[1] >>> 24, // "Universes" ?
                                                    Y,
                                                    Z);
                return true;
            }
        }
        case AuthId_Steam3:
        {
            if(input_type == AuthId_Steam3)
                return false;

            if(input_type == AuthId_Steam2)
            {
                int Z = StringToInt(input[10]);
                int Y = StringToInt(input[8]);
                int W = Z*2+Y;

                Format(output, maxlength, "[U:1:%i]", W);

                return true;
            }
            else
            {
                int W = result[0];

                Format(output, maxlength, "[U:1:%i]", W);
                
                return true;
            }
        }
        case AuthId_SteamID64:
        {
            if(input_type == AuthId_SteamID64)
                return false;

            if(input_type == AuthId_Steam2)
            {
                int Z = StringToInt(input[10]);
                int Y = StringToInt(input[8]);

                //W=Z*2+V+Y
                int V = higherbit;
                int W = Z*2+Y;

                result[0] = W;
                result[1] = V;

                Int64ToString(result, output, maxlength);

                return true;
            }
            else
            {
                int V = higherbit;
                int W = StringToInt(input[5]);

                result[0] = W;
                result[1] = V;

                Int64ToString(result, output, maxlength);

                return true;
            }
        }
    }

    return false;
} 

• 参考：
  stock FormatSteamID | Format steamid type to another | update 18.10.2022 - AlliedModders (alliedmods.net)
  AuthIdType · clients · SourceMod Scripting API Reference (alliedmods.net)