This change provides a common convention for using allocator-dependent
features with:
#![cfg(feature = "alloc")]
When available, `Vec` is imported consistently as `prelude::Vec`, which
means modules that need access to `Vec` can simply do:
use prelude::*;
and if an allocator is available, `Vec` will be in the crate prelude.
This allows all `alloc` vs `std` gating to be handled in `lib.rs`,
`build.rs`, and `prelude.rs` so the rest of the codebase doesn't have to
do any gating whatsoever.
Since Criterion can only benchmark public API, these changes just drop
all internal benchmarks (e.g., benchmarks for field operations). But
those are usually microbenchmarks whose meaning is kind of questionable
anyways, so I don't think this is a big loss.
The `bench` feature disappears, since Criterion works on stable Rust.
The `MontgomeryPoint` struct is now a point on the Kummer line of the Montgomery curve.
The `ProjectivePoint` struct is made private, since its only purpose is
internal to the Montgomery ladder.
The Montgomery ladder takes affine input, making it faster, and produces affine output.
The Edwards-Montgomery correspondence is simplified.
This commit defines a Scalar to hold an integer representing an element of
Z/lZ. Applications like X/Ed25519 that care about the bit-patterns of the
scalars they use can set a specific bit-pattern using the `from_bits`
constructor. Applications that want to treat scalars as integers mod l can use
the `from_bytes_mod_order` constructor. Either way, the constructor ensures
that the integer representing each Scalar is bounded by 2^255 so that the high
bit is set. This means that any Scalar object is always safe to use for scalar
multiplication, while maintaining compatibility with both the Ristretto
use-case and the X/Ed25519 usecase.
compress_edwards() is now named compress() and works only on points
which are in Edwards form. Similarly, compress_montgomery() is now
also called compress(), and it only works on point already in
Mongomery form.
To switch between forms, use to_montgomery().
Conversion from Montgomery directly to Edwards is not yet implemented.
* CHANGE the API requested in
https://github.com/isislovecruft/curve25519-dalek/issues/47,
hopefully for the better.
Having _BASEPOINT_TABLE and _BASEPOINT_POINT means that it's not possible to
use the slow, generic scalar mult in place of the fast, precomputed scalar
mults.
