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better explanation of right-shift operator in halving calculation

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Andreas M. Antonopoulos 2017-07-18 11:52:18 +08:00
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@ -281,7 +281,7 @@ The initial subsidy is calculated in satoshis by multiplying 50 with the +COIN+
The maximum number of halvings allowed is 64, so the code imposes a zero reward (returns only the fees) if the 64 halvings is exceeded. The maximum number of halvings allowed is 64, so the code imposes a zero reward (returns only the fees) if the 64 halvings is exceeded.
Next, the function uses the binary-right-shift operator to divide the reward (+nSubsidy+) by two for each round of halving. In the case of block 277,316, this would binary-right-shift the reward of 5 billion satoshis once (one halving) and result in 2.5 billion satoshis, or 25 bitcoin. The binary-right-shift operator is used because it is more efficient for division by two than integer or floating-point division. Next, the function uses the binary-right-shift operator to divide the reward (+nSubsidy+) by two for each round of halving. In the case of block 277,316, this would binary-right-shift the reward of 5 billion satoshis once (one halving) and result in 2.5 billion satoshis, or 25 bitcoins. The binary-right-shift operator is used because it is more efficient than multiple repeated divisions. To avoid a potential bug, the shift operation is skipped after 63 halvings, and the subsidy is set to 0.
Finally, the coinbase reward (+nSubsidy+) is added to the transaction fees (+nFees+), and the sum is returned. Finally, the coinbase reward (+nSubsidy+) is added to the transaction fees (+nFees+), and the sum is returned.