From 8c97900a802db12f69386bf99c62006c4cc9c366 Mon Sep 17 00:00:00 2001
From: Darnell Andries <dandries@brave.com>
Date: Tue, 2 Sep 2025 17:26:39 -0700
Subject: [PATCH] Use `Wrapping` struct for arithmetic wrapping in `BIG`/`DBIG`
 `cmove`

---
 rust/big.rs  | 29 ++++++++++++++---------------
 rust/dbig.rs | 27 +++++++++++++--------------
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/rust/big.rs b/rust/big.rs
index 30ef8a0..3ee5c08 100644
--- a/rust/big.rs
+++ b/rust/big.rs
@@ -17,6 +17,8 @@
  * limitations under the License.
  */
 
+use core::num::Wrapping;
+
 use crate::arch;
 use crate::arch::Chunk;
 
@@ -214,23 +216,20 @@ impl BIG {
 
     #[inline(never)]
     pub fn cmove(&mut self, g: &BIG, b: isize)  -> Chunk {
-        static mut R:Chunk=0;
-        let w:Chunk;
-        unsafe {
-            R=R.wrapping_add(CONDMS);
-            w=R;
-        }
-        let bb=b as Chunk;
-        let c0=(!bb)&(w+1);
-        let c1=bb+w;
+        let w = Wrapping(CONDMS as Chunk);
+        let bb = Wrapping(b as Chunk);
+        let c0 = !bb & (w + Wrapping(1));
+        let c1 = bb + w;
         for i in 0..NLEN {
-            let s = g.w[i];
-            let t = self.w[i];
-            unsafe{core::ptr::write_volatile(&mut self.w[i],t.wrapping_mul(c0).wrapping_add(s.wrapping_mul(c1))  /* c0*t+c1*s */)}  
-            self.w[i]=self.w[i].wrapping_sub(w.wrapping_mul(t.wrapping_add(s)));
+            let s = Wrapping(g.w[i]);
+            let t = Wrapping(self.w[i]);
+            let c0_t = c0 * t;
+            let c1_s = c1 * s;
+            let w_tssum = w * (t + s);
+            unsafe { core::ptr::write_volatile(&mut self.w[i], (c0_t + c1_s - w_tssum).0) }
         }
-        return 0 as Chunk;
-    }  
+        return 0;
+    }
 
 /*
     pub fn cmove(&mut self, g: &BIG, d: isize)  -> Chunk {
diff --git a/rust/dbig.rs b/rust/dbig.rs
index 300e4bf..67bbb7e 100644
--- a/rust/dbig.rs
+++ b/rust/dbig.rs
@@ -17,6 +17,8 @@
  * limitations under the License.
  */
 
+use core::num::Wrapping;
+
 use crate::arch;
 use crate::arch::Chunk;
 use crate::arch::CONDMS;
@@ -134,22 +136,19 @@ impl DBIG {
 
     #[inline(never)]
     pub fn cmove(&mut self, g: &DBIG, b: isize) -> Chunk {
-        static mut R:Chunk=0;
-        let w:Chunk;
-        unsafe {
-            R=R.wrapping_add(CONDMS);
-            w=R;
-        }
-        let bb=b as Chunk;
-        let c0=(!bb)&(w+1);
-        let c1=bb+w;
+        let w = Wrapping(CONDMS as Chunk);
+        let bb = Wrapping(b as Chunk);
+        let c0 = !bb & (w + Wrapping(1));
+        let c1 = bb + w;
         for i in 0..big::DNLEN {
-            let s = g.w[i];
-            let t = self.w[i];
-            unsafe{core::ptr::write_volatile(&mut self.w[i],t.wrapping_mul(c0).wrapping_add(s.wrapping_mul(c1)))}  
-            self.w[i]=self.w[i].wrapping_sub(w.wrapping_mul(t.wrapping_add(s)));
+            let s = Wrapping(g.w[i]);
+            let t = Wrapping(self.w[i]);
+            let c0_t = c0 * t;
+            let c1_s = c1 * s;
+            let w_tssum = w * (t + s);
+            unsafe { core::ptr::write_volatile(&mut self.w[i], (c0_t + c1_s - w_tssum).0) }
         }
-        return 0 as Chunk;
+        return 0;
     }
 
     /* self+=x */