the meaning of prev_root

[jackzhp]

I don't understand its meaning.

Why for the genesis block(mainnet), it has prev_root 0000000000000000002a8bc32f43277fe9c063b9c99ea252b483941dcd06e217
and for floo net, it is 00000000000000000017ff4903ef366c8f62e3151ba74e41b8332a126542f538?

Thanks.

[jackzhp]

Then I found that 0000000000000000002a8bc32f43277fe9c063b9c99ea252b483941dcd06e217
is the block # of BTC at height 558653(15th Jan 2019 15:00:22)

while 00000000000000000017ff4903ef366c8f62e3151ba74e41b8332a126542f538 is the block # of BTC at height 555959(
28th Dec 2018 20:15:09)

Why Grin contains the info from BTC? very weird.

[tromp]

Not that weird; it serves as proof that the Grin Genesis blocks were generated after those Bitcoin blocks were (similar to the Bitcoin genesis block containing the message “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks”). This further allays possible fears that the chain could have been fast mined before the public.

[jackzhp]

Thanks for responding to me.

OK. then does this really get into the MMR? it say prev_root.

suppose it does not get into the header MMR, then the first node of the header MMR is the blake2b(32) hash of
HeaderEntry(block#0 hash + timestamp + totalDifficult + secondary_scale + isSecondary).
ie. 40ADAD0AEC27797B48840AA9E00472015C21BAEA118CE7A2FF1A82C0F8F5BF82000000005C3E03D600000004000000000000074001 (*****)
and its hash_with_index 0(8 bytes): gives: A4E6257532125F637CED6F3A1D1BD0BDAAF0C77630337DEDC0C14BD3E88F0246

this does not match the block#1.prev_root 5671FB28C1509E422D9B8F60CE90E9AC9041E3B9FEBD34A79C03048844ED2733 (%%%%%)

suppose it(the BTC block hash) does not get into the header MMR, it's the first node, and the genesis block gives the 2nd node. blake2b(32) hash the (***** line) with index 1(the 2nd node), this gives: DC205D06D4358D797B8A03D02EB52DD792BD151B8C64F2D315D6489804109C91
And then the 3rd Node is C0B2622CF9DDD8B22821B1FFCC133AB5EDA5F85812C697C36CDF1370241F7DA8, still not expected (%%%%% line)

Anyone has any idea on this?
I guess I did not get (the ***** line) right, but this is specified in block.rs.

[tromp]

the first node of the header MMR is the blake2b(32) hash of
HeaderEntry(block#0 hash + timestamp + totalDifficult + secondary_scale + isSecondary).

What do you mean by "block#0 hash"?
The HeaderEntry hash is set to the BlockHeader hash which is the Blake2b hash of the prepow header as defined in

https://github.com/mimblewimble/grin/blob/684f0a387ae1ac47e34e68aae2cf94514b86aaf4/core/src/core/block.rs#L322

[jackzhp]

eventually, I found that for header MMR, to build the mountain, only the index + cuckoo_solution is hashed for those leaf nodes, now block#x.prev_root is indeed the root of the header MMR.

[jackzhp]

And the BTC block hash does not get into the MMR.

[tromp]

cuckoo_solution is hashed

Where in the code did you see this happening?