From 4ea0f59e0a5f2aae07566e71c3101484a3d7190f Mon Sep 17 00:00:00 2001
From: jmwample <8297368+jmwample@users.noreply.github.com>
Date: Fri, 26 Jul 2024 10:11:21 -0600
Subject: [PATCH] apply changes from upstream to forked crate

---
 curve25519-elligator2/Cargo.toml                       | 10 ++++++++++
 curve25519-elligator2/src/backend/serial/u32/scalar.rs |  7 +++++--
 curve25519-elligator2/src/backend/serial/u64/scalar.rs |  7 +++++--
 .../src/backend/vector/ifma/edwards.rs                 |  2 +-
 curve25519-elligator2/src/backend/vector/ifma/field.rs |  2 +-
 5 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/curve25519-elligator2/Cargo.toml b/curve25519-elligator2/Cargo.toml
index 242facd0..ebb1c709 100644
--- a/curve25519-elligator2/Cargo.toml
+++ b/curve25519-elligator2/Cargo.toml
@@ -77,3 +77,13 @@ digest = ["dep:digest", "elligator2"]
 
 [target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64"))'.dependencies]
 curve25519-dalek-derive = { version = "0.1.1" }
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+    'cfg(allow_unused_unsafe)',
+    'cfg(curve25519_dalek_backend, values("fiat", "serial", "simd"))',
+    'cfg(curve25519_dalek_diagnostics, values("build"))',
+    'cfg(curve25519_dalek_bits, values("32", "64"))',
+    'cfg(nightly)',
+]
diff --git a/curve25519-elligator2/src/backend/serial/u32/scalar.rs b/curve25519-elligator2/src/backend/serial/u32/scalar.rs
index 2d135d1d..82730675 100644
--- a/curve25519-elligator2/src/backend/serial/u32/scalar.rs
+++ b/curve25519-elligator2/src/backend/serial/u32/scalar.rs
@@ -12,6 +12,7 @@
 
 use core::fmt::Debug;
 use core::ops::{Index, IndexMut};
+use subtle::{Choice, ConditionallySelectable};
 
 #[cfg(feature = "zeroize")]
 use zeroize::Zeroize;
@@ -196,10 +197,12 @@ impl Scalar29 {
         }
 
         // conditionally add l if the difference is negative
-        let underflow_mask = ((borrow >> 31) ^ 1).wrapping_sub(1);
         let mut carry: u32 = 0;
         for i in 0..9 {
-            carry = (carry >> 29) + difference[i] + (constants::L[i] & underflow_mask);
+            let underflow = Choice::from((borrow >> 31) as u8);
+
+            let addend = u32::conditional_select(&0, &constants::L[i], underflow);
+            carry = (carry >> 29) + difference[i] + addend;
             difference[i] = carry & mask;
         }
 
diff --git a/curve25519-elligator2/src/backend/serial/u64/scalar.rs b/curve25519-elligator2/src/backend/serial/u64/scalar.rs
index 1cc2df4a..bcbdc2eb 100644
--- a/curve25519-elligator2/src/backend/serial/u64/scalar.rs
+++ b/curve25519-elligator2/src/backend/serial/u64/scalar.rs
@@ -13,6 +13,7 @@
 
 use core::fmt::Debug;
 use core::ops::{Index, IndexMut};
+use subtle::{Choice, ConditionallySelectable};
 
 #[cfg(feature = "zeroize")]
 use zeroize::Zeroize;
@@ -185,10 +186,12 @@ impl Scalar52 {
         }
 
         // conditionally add l if the difference is negative
-        let underflow_mask = ((borrow >> 63) ^ 1).wrapping_sub(1);
         let mut carry: u64 = 0;
         for i in 0..5 {
-            carry = (carry >> 52) + difference[i] + (constants::L[i] & underflow_mask);
+            let underflow = Choice::from((borrow >> 63) as u8);
+
+            let addend = u64::conditional_select(&0, &constants::L[i], underflow);
+            carry = (carry >> 52) + difference[i] + addend;
             difference[i] = carry & mask;
         }
 
diff --git a/curve25519-elligator2/src/backend/vector/ifma/edwards.rs b/curve25519-elligator2/src/backend/vector/ifma/edwards.rs
index c148bf15..625197e3 100644
--- a/curve25519-elligator2/src/backend/vector/ifma/edwards.rs
+++ b/curve25519-elligator2/src/backend/vector/ifma/edwards.rs
@@ -249,7 +249,7 @@ impl<'a> From<&'a edwards::EdwardsPoint> for NafLookupTable8<CachedPoint> {
     }
 }
 
-#[cfg(target_feature = "avx512ifma,avx512vl")]
+#[cfg(all(target_feature = "avx512ifma", target_feature = "avx512vl"))]
 #[cfg(test)]
 mod test {
     use super::*;
diff --git a/curve25519-elligator2/src/backend/vector/ifma/field.rs b/curve25519-elligator2/src/backend/vector/ifma/field.rs
index deceebd8..993be1d7 100644
--- a/curve25519-elligator2/src/backend/vector/ifma/field.rs
+++ b/curve25519-elligator2/src/backend/vector/ifma/field.rs
@@ -629,7 +629,7 @@ impl<'a, 'b> Mul<&'b F51x4Reduced> for &'a F51x4Reduced {
     }
 }
 
-#[cfg(target_feature = "avx512ifma,avx512vl")]
+#[cfg(all(target_feature = "avx512ifma", target_feature = "avx512vl"))]
 #[cfg(test)]
 mod test {
     use super::*;