arithmetic: Allow use of N0 from outside of arithmetic.

Allow N0 to be const-constructed and expose it outside of `arithmetic`
so that `ec` can start using it.

src/arithmetic.rs

@@ -18,6 +18,7 @@ mod constant;
 pub mod bigint;
 
 pub mod montgomery;
+
 mod n0;
 
 #[allow(dead_code)]

src/arithmetic/bigint.rs

@@ -41,7 +41,6 @@ pub(crate) use self::{
     modulus::{Modulus, OwnedModulus, MODULUS_MAX_LIMBS},
     private_exponent::PrivateExponent,
 };
-use super::n0::N0;
 use crate::{
     arithmetic::montgomery::*,
     bits::BitLength,

src/arithmetic/bigint/modulus.rs

@@ -12,7 +12,7 @@
 // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
-use super::{super::n0::N0, BoxedLimbs, Elem, PublicModulus, Unencoded};
+use super::{BoxedLimbs, Elem, PublicModulus, Unencoded, N0};
 use crate::{
     bits::BitLength,
     cpu, error,
@@ -126,7 +126,7 @@ impl<M> OwnedModulus<M> {
                 debug_assert_eq!(LIMB_BITS, 32);
                 n_mod_r |= u64::from(n[1]) << 32;
             }
-            N0::from(unsafe { bn_neg_inv_mod_r_u64(n_mod_r) })
+            N0::precalculated(unsafe { bn_neg_inv_mod_r_u64(n_mod_r) })
         };
 
         let len_bits = limb::limbs_minimal_bits(&n);

src/arithmetic/montgomery.rs

@@ -12,6 +12,8 @@
 // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
+pub use super::n0::N0;
+
 // Indicates that the element is not encoded; there is no *R* factor
 // that needs to be canceled out.
 #[derive(Copy, Clone)]
@@ -107,10 +109,7 @@ impl ProductEncoding for (RRR, RInverse) {
 }
 
 #[allow(unused_imports)]
-use {
-    super::n0::N0,
-    crate::{bssl, c, limb::Limb},
-};
+use crate::{bssl, c, limb::Limb};
 
 #[cfg(not(any(
     target_arch = "aarch64",

src/arithmetic/n0.rs

@@ -16,16 +16,14 @@ use crate::limb::Limb;
 
 #[derive(Clone, Copy)]
 #[repr(transparent)]
-pub(in super::super) struct N0([Limb; 2]);
+pub struct N0([Limb; 2]);
 
 impl N0 {
     #[cfg(feature = "alloc")]
     pub(super) const LIMBS_USED: usize = 64 / crate::limb::LIMB_BITS;
-}
 
-impl From<u64> for N0 {
     #[inline]
-    fn from(n0: u64) -> Self {
+    pub const fn precalculated(n0: u64) -> Self {
         #[cfg(target_pointer_width = "64")]
         {
             Self([n0, 0])