Define native word size as constant_time::Word.

src/constant_time.rs

@@ -16,6 +16,12 @@
 
 use crate::{c, error};
 
+#[cfg(target_pointer_width = "64")]
+pub(crate) type Word = u64;
+
+#[cfg(target_pointer_width = "32")]
+pub(crate) type Word = u32;
+
 /// Returns `Ok(())` if `a == b` and `Err(error::Unspecified)` otherwise.
 /// The comparison of `a` and `b` is done in constant time with respect to the
 /// contents of each, but NOT in constant time with respect to the lengths of

src/limb.rs

@@ -21,34 +21,20 @@
 use crate::{c, error, polyfill::ArrayFlatMap};
 
 #[cfg(any(test, feature = "alloc"))]
-use crate::bits;
+use crate::{bits, constant_time, polyfill::usize_from_u32};
 
 #[cfg(feature = "alloc")]
 use core::num::Wrapping;
 
 // XXX: Not correct for x32 ABIs.
-#[cfg(target_pointer_width = "64")]
-pub type Limb = u64;
-#[cfg(target_pointer_width = "32")]
-pub type Limb = u32;
-#[cfg(target_pointer_width = "64")]
-pub const LIMB_BITS: usize = 64;
-#[cfg(target_pointer_width = "32")]
-pub const LIMB_BITS: usize = 32;
-
-#[cfg(target_pointer_width = "64")]
-#[derive(Debug, PartialEq)]
-#[repr(u64)]
-pub enum LimbMask {
- True = 0xffff_ffff_ffff_ffff,
- False = 0,
-}
+pub type Limb = constant_time::Word;
+pub const LIMB_BITS: usize = usize_from_u32(Limb::BITS);
 
-#[cfg(target_pointer_width = "32")]
+#[cfg_attr(target_pointer_width = "64", repr(u64))]
+#[cfg_attr(target_pointer_width = "32", repr(u32))]
 #[derive(Debug, PartialEq)]
-#[repr(u32)]
 pub enum LimbMask {
- True = 0xffff_ffff,
+ True = Limb::MAX,
  False = 0,
 }
 

src/polyfill.rs

@@ -21,6 +21,11 @@ pub const fn u64_from_usize(x: usize) -> u64 {
  x as u64
 }
 
+#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
+pub const fn usize_from_u32(x: u32) -> usize {
+ x as usize
+}
+
 #[cfg(all(target_arch = "aarch64", target_pointer_width = "64"))]
 #[allow(clippy::cast_possible_truncation)]
 pub fn usize_from_u64(x: u64) -> usize {