From: Chris Duncan <chris@zoso.dev>
Date: Fri, 2 Oct 2026 05:16:26 +0000 (-0700)
Subject: Eliminate a scratch buffer by reusing parameter.
X-Git-Url: https://git.codecow.com/?a=commitdiff_plain;h=408e70c87a74f69868c83256b3994405ab8afeb1;p=nano25519.git

Eliminate a scratch buffer by reusing parameter.
---

diff --git a/src/assembly/ed25519/p.ts b/src/assembly/ed25519/p.ts
index c1a7abb..e36a98e 100644
--- a/src/assembly/ed25519/p.ts
+++ b/src/assembly/ed25519/p.ts
@@ -248,20 +248,21 @@ export function ge_sub_cached (r: ge_p1p1, p: ge_p3, q: ge_cached): void {
 	fe_add(r.T, t0, r.T)
 }
 
-const ge_sub_precomp_t0: FieldElement = fe()
 /**
- * r = p - q
+ * `r = p - q`
+ *
+ * `p.Z` is doubled and stored to itself because its value is not used again
+ * before being reassigned at the only call site of this function.
  */
 export function ge_sub_precomp (r: ge_p1p1, p: ge_p3, q: ge_precomp): void {
-	const t0 = ge_sub_precomp_t0
 	fe_add(r.X, p.Y, p.X)
 	fe_sub(r.Y, p.Y, p.X)
 	fe_mul(r.Z, r.X, q.yminusx)
 	fe_mul(r.Y, r.Y, q.yplusx)
 	fe_mul(r.T, q.xy2d, p.T)
-	fe_dbl(t0, p.Z)
+	fe_dbl(p.Z, p.Z)
 	fe_sub(r.X, r.Z, r.Y)
 	fe_add(r.Y, r.Z, r.Y)
-	fe_sub(r.Z, t0, r.T)
-	fe_add(r.T, t0, r.T)
+	fe_sub(r.Z, p.Z, r.T)
+	fe_add(r.T, p.Z, r.T)
 }