Adjust readme and ed25519 docs

README.md

@@ -363,7 +363,7 @@ import { randomBytes } from '@noble/hashes/utils';
 
 const Fp = Field(2n ** 255n - 19n);
 const ed25519 = twistedEdwards({
-  a: -1n,
+  a: Fp.create(-1n),
   d: Fp.div(-121665n, 121666n), // -121665n/121666n mod p
   Fp: Fp,
   n: 2n ** 252n + 27742317777372353535851937790883648493n,
@@ -887,7 +887,6 @@ Upgrading from [@noble/bls12-381](https://github.com/paulmillr/noble-bls12-381):
     - PointG2.fromSignature -> Signature.decode, PointG2.toSignature ->  Signature.encode
 - Fp2 ORDER was corrected
 
-
 ## Resources
 
 Useful articles about the library or its primitives:

src/ed25519.ts

@@ -97,13 +97,13 @@ const Fp = Field(ED25519_P, undefined, true);
 
 const ed25519Defaults = {
   // Param: a
-  a: BigInt(-1),
-  // Equal to -121665/121666 over finite field.
+  a: BigInt(-1), // Fp.create(-1) is proper; our way still works and is faster
+  // d is equal to -121665/121666 over finite field.
   // Negative number is P - number, and division is invert(number, P)
   d: BigInt('37095705934669439343138083508754565189542113879843219016388785533085940283555'),
   // Finite field 𝔽p over which we'll do calculations; 2n ** 255n - 19n
   Fp,
-  // Subgroup order: how many points ed25519 has
+  // Subgroup order: how many points curve has
   // 2n ** 252n + 27742317777372353535851937790883648493n;
   n: BigInt('7237005577332262213973186563042994240857116359379907606001950938285454250989'),
   // Cofactor