I read everywhere that segwit2x activates at blocks 494784, around 15 or 16 of November.

I did just checkout the segwit2x codebase doing:

git clone https://github.com/btc1/bitcoin

And I can see that I'm on a branch called "segwit2x".

I tried to search every single file for any hint of block 494784, 494783 or 494785 but couldn't find anything.

I've got many technical questions regarding segwit2x and I wanted to dig into the source code to find answers.

Seen that I couldn't find anything, my first technical question is this one: where's the code related to block 494784 at which segwit2x is supposed to happen?

1 Answer 1


It is referenced relatively, namely by using the parameter BIP102HeightDelta. The hardfork is 3 months after the block that Segwit was actived and the number of blocks after is equal to 90(days)*144(blocks/day)(https://github.com/btc1/bitcoin/blob/385cbc994f35d36cefdab8c1c00ebfaceb55cfc6/src/chainparams.cpp#L78)

Try to look for that parameter. It will show up that it is used here to define if the 3 months have passed to activate 2MB or not (https://github.com/btc1/bitcoin/blob/385cbc994f35d36cefdab8c1c00ebfaceb55cfc6/src/validation.cpp#L2934 and https://github.com/btc1/bitcoin/blob/385cbc994f35d36cefdab8c1c00ebfaceb55cfc6/src/validation.cpp#L1853 and https://github.com/btc1/bitcoin/blob/385cbc994f35d36cefdab8c1c00ebfaceb55cfc6/src/consensus/consensus.h#L24).

  • ooooh gotcha +1: thank you very much... I was surprised I couldn't find anything but didn't realize they were using a computation starting from the original segwit! Oct 30, 2017 at 18:55

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