During circuit configuration, fixed columns can be marked as suitable
for containing arbitrary constant values (i.e. the columns aren't
encumbered by constraints that preclude arbitrary values).
During synthesis, circuits can now request that the layouter assign
an advice cell within a region, to some specified constant value. It
is the layouter's responsibility to find space within the previously
marked fixed columns, in which to assign the constant.
This commit intentionally does not compile.
Circuit developers need to use selectors (or equivalent) to prevent their
custom gates from being active on unusable rows. By marking the advice
cells in these rows as "poisoned" and tracking this through expressions,
we can provide a better error message to developers that indicates the
missing selector issue.
Closeszcash/halo2#329.
This is the beginning of the process to enable full floor planning
capabilities in `halo2`. For now, all that a floor planner can do is
synthesize a circuit, which makes it no more powerful than a layouter,
but easier to use (as moving to a multi-pass layouter no longer requires
changes to `Circuit::synthesize`).
This is more useful for developers, as the absolute cell row may be
obfuscated by the layouter, whereas the offset within a row is controlled
by the developer.
Current layouters measure the shape of regions by looking at the cells
they assign. If a chip developer forgets to assign a cell in a region,
it is possible for active gates to "stick out" past the edge of a
measured region shape.
`MockProver` checks that all active gates have their cells assigned,
but this was previously checked globally. If a layouter happened to
position the buggy region such that the dangling gate overlapped an
assigned cell in in adjacent region, this check would pass.
In this commit, we extend the check to be per-region. We map enabled
selectors and assigned cells to a specific region, and then if a gate
is active within a region, we require that its cells be assigned within
that same region.
Closeszcash/halo2#297.
Enabling selectors to be used in gates at non-zero rotations leads to
confusing gates, and inhibits our ability to create visualizations of
circuits. In most cases, a gate can be rearranged so that the selectors
have no rotation; in cases where cross-gate selector optimisations are
required, these can still be implemented using fixed columns.
The closure passed to `ConstraintSystem::create_gate` can now return:
- Tuples of `(&'static str, Expression<F>)`
- Anything implementing `IntoIterator` (e.g. `Some(Expression<F>)`)
The simple example was broken because it uses an instance column in a
gate. MockProver now assumes all instance cells are assigned to, since
this happens outside the circuit and outside its purview.
Sean Bowe
str4d
therealyingtong
Daira Hopwood
Jack Grigg