Added static version of toScalar

src/lib/provable/scalar-field.ts

@@ -1,6 +1,5 @@
 import { Fq } from '../../bindings/crypto/finite-field.js';
-import { createField } from './core/field-constructor.js';
-import { createForeignField } from './foreign-field.js';
+import { ForeignField, createForeignField } from './foreign-field.js';
 import { field3ToShiftedScalar } from './gadgets/native-curve.js';
 import { Provable } from './provable.js';
 import { Scalar } from './scalar.js';
@@ -10,14 +9,21 @@ export { ScalarField };
 /**
  * ForeignField representing the scalar field of Pallas and the base field of Vesta
  */
-class ScalarField extends createForeignField(
-  Fq.modulus
-) {
+class ScalarField extends createForeignField(Fq.modulus) {
   /**
    * Provable method to convert a {@link ScalarField} into a {@link Scalar}
    */
   public toScalar(): Scalar {
-    const field3 = this.value;
+    return ScalarField.toScalar(this);
+  }
+
+  public static toScalar(field: ForeignField) {
+    if (field.modulus !== Fq.modulus) {
+      throw new Error(
+        'Only ForeignFields with Fq modulus are convertable into a scalar'
+      );
+    }
+    const field3 = field.value;
     const shiftedScalar = field3ToShiftedScalar(field3);
     return Scalar.fromShiftedScalar(shiftedScalar);
   }
@@ -27,12 +33,10 @@ class ScalarField extends createForeignField(
    */
   static fromScalar(s: Scalar): ScalarField {
     if (s.lowBit.isConstant() && s.high254.isConstant()) {
-      return new ScalarField(
-        ScalarField.from(s.toBigInt())
-      );
+      return new ScalarField(s.toBigInt());
     }
     const field = Provable.witness(ScalarField.provable, () => {
-      return s.toBigInt()
+      return s.toBigInt();
     });
     const foreignField = new ScalarField(field);
     const scalar = foreignField.toScalar();