Add the `deferred` module with a `DeferredField` trait that enables
accumulating multiple unreduced products before performing a single
reduction. The trait uses an accumulation-based API: callers feed
factor pairs into an `Accumulator` via `mul_accumulate` /
`square_accumulate`, then call `reduce` once at the end.
For now, both Fp and Fq implement the trait with `Accumulator = Self`,
performing eager reduction on each accumulation. A later commit will
swap in a wide accumulator that defers reduction for real.
The module is feature-gated behind the `deferred` feature flag.
The traits of ec-gpu changed a bit, there's now also a `GpuName`
trait that needs to be implemented.
BREAKING CHANGE: `ec-gpu` v0.2 traits are not compatible with v0.1
All dependencies that use `ec-gpu` need to be on v0.2.
This commit introduces a new feature called "gpu", which enables an
`ec_gpu:GpuField` implementation of `Fp` and `Fq`. This enables the
field arithmetics to be run on a GPU.
The code to convert from a u64 to a u32 vector was taken from
07a84f9727/src/lib.rs (L102-L108)
Now that we have a default implementation of `SqrtRatio::sqrt_ratio`, we
can use it and `FieldExt` in no-std environments.
We introduce an `alloc` feature flag to form a common feature dependency
between `std` and `sqrt-table`. It is currently unused directly, but
will be used after `CurveAffine` is refactored to remove the `std`
dependency.
Closeszcash/pasta_curves#25.
We re-introduce the Tonelli-Shank square root algoritm that was removed
in zcash/halo2#120, to use in no-std mode (the table-based impl requires
allocations, and also uses 29kiB of memory which is a problem for
constrained environments that typically need no-std).
The `Curve` trait is now `CurveExt: group::prime::PrimeCurve`, and
`CurveAffine` is now `CurveAffine: group::prime::PrimeCurveAffine`.
There is no `CurveAffine` trait in `group`, and it's a widely-used
trait in this crate, so we don't rename it to `CurveAffineExt`.
