Eliminate another scratch buffer.

diff --git a/src/assembly/ed25519/p.ts b/src/assembly/ed25519/p.ts
index f43c36247bf6525fbb2adac0ea9e8eb2b655187b..6be80190737c60210dec1991ab65bed8d2f629f3 100644 (file)
--- a/src/assembly/ed25519/p.ts
+++ b/src/assembly/ed25519/p.ts
@@ -190,24 +190,25 @@ export function ge_add_cached (r: ge_p1p1, p: ge_p3, q: ge_cached): void {
        fe_sub(r.T, t0, r.T)
 }
 
-const ge_add_precomp_t0: FieldElement = fe()
 /**
- * r = p + q
+ * `r = p + q`
+ *
+ * `p.Z` is doubled and stored to itself because its value is not referenced
+ * again before being reassigned at all three call sites of this function.
  */
 //@ts-expect-error
 @inline
 export function ge_add_precomp (r: ge_p1p1, p: ge_p3, q: ge_precomp): void {
-       const t0 = ge_add_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.yplusx)
        fe_mul(r.Y, r.Y, q.yminusx)
        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_add(r.Z, t0, r.T)
-       fe_sub(r.T, t0, r.T)
+       fe_add(r.Z, p.Z, r.T)
+       fe_sub(r.T, p.Z, r.T)
 }
 
 const ge_sub_p3_q_cached = new ge_cached()