reward schedule – The place is the bitcoin supply code is the 21 million exhausting cap said?

The place is the bitcoin supply code is the 21 million exhausting cap said?

Nowhere, truly, as a result of 21 million isn’t the precise restrict.

The related code is this:

CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
{
    int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
    // Pressure block reward to zero when proper shift is undefined.
    if (halvings >= 64)
        return 0;

    CAmount nSubsidy = 50 * COIN;
    // Subsidy is lower in half each 210,000 blocks which can happen roughly each 4 years.
    nSubsidy >>= halvings;
    return nSubsidy;
}

// consensusParams.nSubsidyHalvingInterval = 210000.

It computes the utmost subsidy a miner can declare at a given block peak, and this operate successfully controls Bitcoin’s inflation schedule. The usually-stated “21 million” restrict is simply the approximate results of summing all cash introduced into circulation.

The code, in brief, implements the next:

• The primary 210000 blocks (roughly 4 years) permit as much as 50 BTC subsidy every.
• Then 210000 blocks with 25 BTC every
• Then 210000 blocks with 12.5 BTC every
• …
• After 10 halvings, the subsidy turns into 0.04882812 BTC slightly than 0.048828125 (which would want half-satoshi precision, and the code makes use of integer division which rounds down).
• After 34 halvings, the subsidy turns into 0.

If one sums up all of the subsidy values over all halvings, the result’s 20999999.9769 BTC, not 21000000 BTC. Although, as a result of varied trivialities, that is additionally not the true restrict; this reply goes into extra element.

Now, the code does additionally comprise this fixed:

/** No quantity bigger than this (in satoshi) is legitimate.
 *
 * Observe that this fixed is *not* the overall cash provide, which in Bitcoin
 * at the moment occurs to be lower than 21,000,000 BTC for varied causes, however
 * slightly a sanity verify. As this sanity verify is utilized by consensus-critical
 * validation code, the precise worth of the MAX_MONEY fixed is consensus
 * essential; in uncommon circumstances like a(nother) overflow bug that allowed
 * for the creation of cash out of skinny air modification may result in a fork.
 * */
static constexpr CAmount MAX_MONEY = 21000000 * COIN;

which, because the remark explains, doesn’t truly management the overall provide (as that is slightly the results of summing all of the subsidy), however is used as a sanity verify in lots of locations.