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barretenberg/cpp/src/barretenberg/vm2/tracegen/lib/README.md

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 **Current state**
 
-- Lookups are supported, permutations are not. Lookups are "easy" to use when looking up into a precomputed table, and there is an example. There is no example for looking up into a dynamic (runtime) table, and it's a bit more difficult.
-- Lookups work but you need to manually create a LookupInto class and add it to the tracehelper. You can use the autogenerated `lookup_settings` class to specify the columns, etc.
-- Counts are computed for you, but you need to specify a way (`find_dst_row`) to find a row in the destination table. This should be easy and fast for precomputed tables, but you will need to either do a search or create an index for runtime tables (not done yet).
+- Both lookups and permutations are supported.
+  - When you lookup into a precomputed table, you need to define a fast way to find the row for a tuple. See bitwise example.
+  - When you lookup into a non-precomputed (dynamic) table, you can use the class `LookupIntoDynamicTable`. There is an example.
+  - For permutations you need to use the `PermutationBuilder` class.
+- Lookups and permutations work but you need to manually create a LookupInto class and add it to the tracehelper. You can use the autogenerated `lookup_settings` class to specify the columns, etc. See examples.
+- Counts are computed for you, but you need to specify a way (`find_dst_row`) to find a row in the destination table.
 - Calculation of inverses is actually very inefficient for lookups into big tables, in particular for precomputed tables. This is not new in this design: the inverses are calculated for every row with either the source or destination selector active. See possible improvements (INVERSES_SELECTOR).
 - Calculation of inverses probes the whole circuit (not new in this design): the logderiv library probes every row and computes the inverse when needed. See possible improvements (INVERSES_PROBING)
 
 **Future work**
 
 Mostly notes for myself.
 
-- Add example of efficient `find_dst_row` for lookup into dynamic.
-- Add example of lookup into dynamic.
 - (INVERSES_SELECTOR) We should be able to compute inverses only for rows that either (1) have the source selector active or, (2) have a non-zero count. The easies way would be to add a new selector column sel_count_nonzero and use that as selector insted of the dst selector. We would also add a new constrain `sel_count_nonzero == 1 <=> count != 0`. We could possibly just bake this into the lookup relation (see predicates) and avoid the extra column.
 - (INVERSES_PROBING) The current implementation probes the whole circuit but the trace object lets you efficiently visit non-zero rows. Since we now set dummy values to the inverse column, we can just visit the non-zero elements and compute the inverses for them.