Remove `std` feature flag

Closes zcash/pasta_curves#27.

Cargo.toml

@@ -25,7 +25,7 @@ rand_xorshift = "0.3"
 [[bench]]
 name = "hashtocurve"
 harness = false
-required-features = ["std"]
+required-features = ["alloc"]
 
 [[bench]]
 name = "fp"
@@ -38,7 +38,7 @@ harness = false
 [[bench]]
 name = "point"
 harness = false
-required-features = ["std"]
+required-features = ["alloc"]
 
 [dependencies]
 blake2b_simd = { version = "0.5", default-features = false }
@@ -52,8 +52,7 @@ subtle = { version = "2.3", default-features = false }
 lazy_static = { version = "1.4.0", optional = true }
 
 [features]
-default = ["bits", "sqrt-table", "std"]
+default = ["bits", "sqrt-table"]
 alloc = ["group/alloc"]
 bits = ["ff/bits"]
 sqrt-table = ["alloc", "lazy_static"]
-std = ["alloc"]

src/arithmetic.rs

@@ -7,8 +7,6 @@
 mod curves;
 mod fields;
 
-pub(crate) use fields::*;
-
 pub use curves::*;
 pub use fields::*;
 

src/arithmetic/curves.rs

@@ -1,28 +1,26 @@
 //! This module contains the `Curve`/`CurveAffine` abstractions that allow us to
 //! write code that generalizes over a pair of groups.
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 use group::prime::{PrimeCurve, PrimeCurveAffine};
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 use super::{FieldExt, Group};
 
-#[cfg(feature = "std")]
-use std::{
-    boxed::Box,
-    ops::{Add, Mul, Sub},
-};
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+#[cfg(feature = "alloc")]
+use core::ops::{Add, Mul, Sub};
 
 /// This trait is a common interface for dealing with elements of an elliptic
 /// curve group in a "projective" form, where that arithmetic is usually more
 /// efficient.
 ///
-/// Currently requires the `std` feature flag because of `hash_to_curve`, and
-/// `CurveAffine::{read, write}`.
-#[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+/// Requires the `alloc` feature flag because of `hash_to_curve`.
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub trait CurveExt:
     PrimeCurve<Affine = <Self as CurveExt>::AffineExt>
     + group::Group<Scalar = <Self as CurveExt>::ScalarExt>
@@ -89,8 +87,10 @@ pub trait CurveExt:
 
 /// This trait is the affine counterpart to `Curve` and is used for
 /// serialization, storage in memory, and inspection of $x$ and $y$ coordinates.
-#[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+///
+/// Requires the `alloc` feature flag because of `hash_to_curve` on [`CurveExt`].
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub trait CurveAffine:
     PrimeCurveAffine<
         Scalar = <Self as CurveAffine>::ScalarExt,
@@ -130,15 +130,15 @@ pub trait CurveAffine:
 }
 
 /// The affine coordinates of a point on an elliptic curve.
-#[cfg(feature = "std")]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 #[derive(Clone, Copy, Debug, Default)]
 pub struct Coordinates<C: CurveAffine> {
     pub(crate) x: C::Base,
     pub(crate) y: C::Base,
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 impl<C: CurveAffine> Coordinates<C> {
     /// Returns the x-coordinate.
     ///
@@ -169,7 +169,7 @@ impl<C: CurveAffine> Coordinates<C> {
     }
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 impl<C: CurveAffine> ConditionallySelectable for Coordinates<C> {
     fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
         Coordinates {

src/curves.rs

@@ -6,8 +6,8 @@ use core::fmt;
 use core::iter::Sum;
 use core::ops::{Add, Mul, Neg, Sub};
 
-#[cfg(feature = "std")]
-use std::boxed::Box;
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
 
 use ff::{Field, PrimeField};
 use group::{
@@ -19,9 +19,10 @@ use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
 use super::{Fp, Fq};
+use crate::arithmetic::Group;
 
-#[cfg(feature = "std")]
-use crate::arithmetic::{Coordinates, CurveAffine, CurveExt, FieldExt, Group};
+#[cfg(feature = "alloc")]
+use crate::arithmetic::{Coordinates, CurveAffine, CurveExt, FieldExt};
 
 macro_rules! new_curve_impl {
     (($($privacy:tt)*), $name:ident, $name_affine:ident, $iso:ident, $base:ident, $scalar:ident,
@@ -102,8 +103,8 @@ macro_rules! new_curve_impl {
             }
         }
 
-        #[cfg(feature = "std")]
-        #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+        #[cfg(feature = "alloc")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
         impl group::WnafGroup for $name {
             fn recommended_wnaf_for_num_scalars(num_scalars: usize) -> usize {
                 // Copied from bls12_381::g1, should be updated.
@@ -123,7 +124,8 @@ macro_rules! new_curve_impl {
             }
         }
 
-        #[cfg(feature = "std")]
+        #[cfg(feature = "alloc")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
         impl CurveExt for $name {
             type ScalarExt = $scalar;
             type Base = $base;
@@ -695,7 +697,8 @@ macro_rules! new_curve_impl {
             }
         }
 
-        #[cfg(feature = "std")]
+        #[cfg(feature = "alloc")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
         impl CurveAffine for $name_affine {
             type ScalarExt = $scalar;
             type Base = $base;
@@ -779,7 +782,6 @@ macro_rules! new_curve_impl {
         impl_binops_multiplicative!($name, $scalar);
         impl_binops_multiplicative_mixed!($name_affine, $scalar, $name);
 
-        #[cfg(feature = "std")]
         impl Group for $name {
             type Scalar = $scalar;
 
@@ -880,7 +882,7 @@ macro_rules! impl_projective_curve_specific {
     };
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 macro_rules! impl_projective_curve_ext {
     ($name:ident, $iso:ident, $base:ident, special_a0_b5) => {
         fn hash_to_curve<'a>(domain_prefix: &'a str) -> Box<dyn Fn(&[u8]) -> Self + 'a> {

src/lib.rs

@@ -12,7 +12,7 @@
 #[cfg(feature = "alloc")]
 extern crate alloc;
 
-#[cfg(any(feature = "std", test))]
+#[cfg(test)]
 #[macro_use]
 extern crate std;
 
@@ -25,7 +25,7 @@ pub mod arithmetic;
 pub mod pallas;
 pub mod vesta;
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 mod hashtocurve;
 
 pub use curves::*;
@@ -33,7 +33,7 @@ pub use fields::*;
 
 pub extern crate group;
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_endo_consistency() {
     use crate::arithmetic::{CurveExt, FieldExt};

src/pallas.rs

@@ -14,7 +14,7 @@ pub type Point = Ep;
 /// A Pallas point in the affine coordinate space (or the point at infinity).
 pub type Affine = EpAffine;
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 #[allow(clippy::many_single_char_names)]
 fn test_iso_map() {
@@ -65,7 +65,7 @@ fn test_iso_map() {
     assert!(p2 == p.double());
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_iso_map_identity() {
     use crate::arithmetic::CurveExt;
@@ -100,7 +100,7 @@ fn test_iso_map_identity() {
     assert!(bool::from(p.is_identity()));
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_map_to_curve_simple_swu() {
     use crate::arithmetic::CurveExt;
@@ -135,7 +135,7 @@ fn test_map_to_curve_simple_swu() {
     );
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_hash_to_curve() {
     use crate::arithmetic::CurveExt;

src/vesta.rs

@@ -14,7 +14,7 @@ pub type Point = Eq;
 /// A Vesta point in the affine coordinate space (or the point at infinity).
 pub type Affine = EqAffine;
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_map_to_curve_simple_swu() {
     use crate::arithmetic::CurveExt;
@@ -49,7 +49,7 @@ fn test_map_to_curve_simple_swu() {
     );
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "alloc")]
 #[test]
 fn test_hash_to_curve() {
     use crate::arithmetic::CurveExt;