How to get next Zcash halving height?

Technology
1

Hello friends!
I’m working on this simple “Zcash Halving Countdown”, but I’m not sure how to get the next halving block height.
Reading the Zcash Protocol Specification page 134, I got the following formula:

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image1110×178 22.8 KB

But this formula returns the halving number, e.g. 0, 1, 2, and so on…

I can bruteforce every block height incremently, until halving == 2, but I don’t like this solution.

I would like to know if there’s a formula to get the next halving height, or the remaining blocks until next halving?

edit
Running a bruteforce for few iterations:

Next halving: 2726400
Next halving: 4406400
Next halving: 6086400

Looks like halvings occurs every 1680000 blocks, is that correct?

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2

If you look at the equation, N changes every PostBlossomHalvingInterval.

PS: It is a staircase function.

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3

Hello @hanh
Could you share more details here please ?

4

Hello @hanh
Please do it fast so we could work on it .

5

postBlossomHalvingInterval is defined by:

const postBlossomHalvingInterval = Math.floor(preBlossomHalvingInterval * blossomPoWTargetSpacingRatio)

Where:

  • preBlossomHalvingInterval is a constant with the value 840000
  • blossomPoWTargetSpacingRatio is the ratio between:
    • preBlossomPoWTargetSpacing = 150
    • postBlossomPoWTargetSpacing = 75

Meaning postBlossomHalvingInterval equals 840000 * 2 = 1680000.

So N changes every 1680000 blocks counting from the first halving, e.g.:

Halving N Height
1 1046400
2 2726400
3 4406400

Not 100% sure, but I think this is correct.

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6

Full javascript code for height > SlowStartShift AND isBlossomActivated(height)

function calculateHalvingNumber(height) {
    const blossomActivationHeight = 653600;
    const preBlossomHalvingInterval = 840000;
    
    const preBlossomPoWTargetSpacing = 150;
    const postBlossomPoWTargetSpacing = 75;

    const blossomPoWTargetSpacingRatio = preBlossomPoWTargetSpacing / postBlossomPoWTargetSpacing; 
    const postBlossomHalvingInterval = Math.floor(preBlossomHalvingInterval * blossomPoWTargetSpacingRatio)

    const slowStartInterval = 20000;
    const slowStartShift = slowStartInterval / 2;

    const halving = Math.floor(( (blossomActivationHeight - slowStartShift) / preBlossomHalvingInterval ) + ( (height - blossomActivationHeight) / postBlossomHalvingInterval ));

    return halving;
}
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