Remaining host functions for FxDAO: 5/11 #43
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bbyalcinkaya
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| <instrs> hostCall ( "env" , "kasmer_set_ledger_timestamp" , [ i64 .ValTypes ] -> [ .ValTypes ] ) | ||
| => loadObject(HostVal(TIMESTAMP)) | ||
| ~> setLedgerTimestamp | ||
| ~> toSmall(Void) |
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@bbyalcinkaya, could you please elaborate a bit on the presence of toSmall at the end of the rewriting operation? After going through its implementation, it is not immediately clear to me why we should leave it at the K cell at the end of certain operations.
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My current understanding is that it is working as some sort of a return value for this host function (as in it is returning nothing, in this case), but I'd like to double check.
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@ACassimiro That's correct, it is used as a return value here. toSmall converts ScVals to HostVals. When a HostVal is on top of the <instrs> cell, it is executed as i64.const _ instruction: rule.
| syntax InternalInstr ::= "vecGet" [symbol(vecGet)] | ||
| // ---------------------------------------------------- | ||
| rule [vecGet]: | ||
| <instrs> vecGet => VEC {{ I }} orDefault HostVal(0) ... </instrs> // use 'orDefault' to avoid non-total list lookup |
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@bbyalcinkaya could you please elaborate on how orDefault operates here? And how it is used to avoid a scenario of non-total list lookup? I'm not entirely familiar with this production, so if you have a reference for me to take a deeper look into it, it would be more than enough.
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It is a typed and total list lookup defined here. It returns the default value if the index is out of bounds or the list item at that index is not a HostVal.
I could've used the normal list lookup but that would require:
- projection cast on the list lookup result because
_ [_]returnsKItem:{VEC[I]}:>HostVal - side condition to check the list item sort:
isHostVal(VEC[I]) preserves-definednessattribute to avoid booster backend fallbacks (and manually check if it actually does)
This PR implements 5/11 of the remaining host functions needed for the FxDAO vaults contract:
get_ledger_timestamp("x" "4")kasmer_set_ledger_timestampdel_contract_data("l" "2")vec_get("v" "1")vec_len("v" "3")vec_push_back("v" "6")