That rule is enough, if no more than 21 million bitcoins can be created, then the maximum supply is 21 million. Bitcoin is not like gold that can be found on asteroids or other planets, mining is the only possible source of new coins. It would be redundant to keep track of existing supply with every new block, Satoshi did not implement it, because it would be a waste of space and processing power.

The reward is havling for every certain period, not for the every block after it was mined so definitely its possible to mine the 21 million bitcoins which is expected to happen in 2140 by that time no one who are discussing about this will be alive.

Why only 21 million? Only satoshi knows the reason, probably it was his lucky number!

Sure. That is more accurate, but "'Satoshi set the total supply of bitcoins to 21 Million' is nonsense" is hyperbole. Or as expressed in your terms, your title is nonsense.




That constant is used only for validation. It is not used to limit the number of coins. You overlooked the comment that immediately precedes the line you quoted:

But, if it's used for validation, doesn't it also limit it too? If you change the block reward and leave that field same, will you be able to bypass the 21 million?

It's uses don't affect the limit.  If the limit were increased, its use for validation might be impacted, certain valid transactions might be rejected, and certain tests would be invalidated.

Note also that the actual limit is not (and has never been) exactly 21 million.

I want to be pedantic.  That line doesn't actually limit the maximum number of coins!

Only the halving of subsidy limits the maximum number of coins.

MAX_MONEY is used in various places to clamp transaction amounts. For example, a transaction can't pay an output more than MAX_MONEY coins (as that would just be impossible, so any number over MAX_MONEY is invalid).  This is just as odolvlobo says.

If you broke the halving but left MAX_MONEY in place the system could get more than 21m BTC, though you might trigger bugs and crashes if more than 21M got spent at once in a single transaction.

This is deep in the weeds and inconsequential,  but since we were already being pedantic we ought not be half-assed about it.  Only full-assed pedantry for me!

All that said, saying Satoshi set the limit to 21M BTC is accurate enough in my view.  I mean, if you want to get really detailed he pressed buttons that commanded logic gates by switching electrons ... and so on.  Shall we really say that Satoshi's mother set the limit by giving birth to Satoshi, or her mother by giving birth to her, or the limit was set when some ape that reached out and touched a black monolith giving birth to intelligent life and the inevitable creation of Bitcoin?   At some point you've got to approximate. Saying Satoshi set a specific limit gets the point across without getting into the weeds, unless the subsidy decline is actually relevant to your conversation.

Moreover, if you start talking about to newbies about rewards going down they often end up thinking mining becomes slower and slower and eventually blocks won't be created anymore.  Giving people too much detail often confuses them.

Correct me if I'm wrong, but I was also thinking more in the line with what FatFork wrote. This whole halving thing means that there will be a division by two going essentially ad infinitum, just like in the Ancient Dichotomy paradox by Zeno. Unless, of course, some limit like 1 Satoshi (or more 'cause there are probably things I haven't taken into account here) finishes this process. At that point, however, it's possible that Satoshis will get divided into even smaller bits, I think, so when the amount will be reaching 21 million forever. Or does the point that we won't have precisely 21 million mean that this number can somehow be exceeded? In that case, the validation line in the code that was discussed above would become a problem, no?

Yes, you're right, sorry. Judging the source code, it's only used to prevent another overflow incident. (just like in block 74638). Although, you do have to change it if you fork Bitcoin Core, otherwise you won't be able to create an output spending more than 21 million coins.

To put it simply, Bitcoin nodes don't sum all the bitcoins and check if there are more than 21 million. (This is how a newbie would think of it)

I don't know if MAX_MONEY is being used outside main.cpp, but that's its only use in that file:

Changes in the code may occur to upgrade the software, but the consensus rules will remain the same. There isn't anything to be agreed, if you don't believe they should be 21M, you can leave Bitcoin. If the majority of the people that run a node, believe that Bitcoin should have more than 21M coins, they're free to change the block rewards. They'll have to comprehend, though, that they'll instantly stop being the majority.

That, also, answers to the next part of your post, which IMO isn't made to be taken seriously.

Yes, thank you. I made a slight error in the calculation because I rounded to the eighth decimal place. The exact figure (after the 33rd halving) is 20999999.9769 BTC.

Your issue really seems to be just semantic. Satoshi decided by writing the code that there is a supply cap at 21 million Bitcoins. What exactly is the problem with that sentence? He put the code such that based on mathematics that cap of 21 million proves valid. Sure, if someone asks you how many Bitcoins there will be you should provide the mathematical explanation. If someone asks you why that is the case or why exactly that number was chosen, your answer should be "because Satoshi decided that way". He could have decided any other number. From an educational perspective the mathematical answer should be first choice, but it is Satoshi who ultimately chose that number.