feat: add grumpkin curve support (#1729)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: yelhousni

backend/witness/vector.go

@@ -10,6 +10,7 @@ import (
 	fr_bls12381 "github.com/consensys/gnark-crypto/ecc/bls12-381/fr"
 	fr_bn254 "github.com/consensys/gnark-crypto/ecc/bn254/fr"
 	fr_bw6761 "github.com/consensys/gnark-crypto/ecc/bw6-761/fr"
+	fr_grumpkin "github.com/consensys/gnark-crypto/ecc/grumpkin/fr"
 	"github.com/consensys/gnark-crypto/field/babybear"
 	"github.com/consensys/gnark-crypto/field/koalabear"
 	"github.com/consensys/gnark/internal/smallfields/tinyfield"
@@ -28,6 +29,9 @@ func newVector(field *big.Int, size int) (any, error) {
 	case ecc.BW6_761:
 		return make(fr_bw6761.Vector, size), nil
 	default:
+		if field.Cmp(ecc.GRUMPKIN.ScalarField()) == 0 {
+			return make(fr_grumpkin.Vector, size), nil
+		}
 		if field.Cmp(tinyfield.Modulus()) == 0 {
 			return make(tinyfield.Vector, size), nil
 		}
@@ -59,6 +63,10 @@ func newFrom(from any, n int) (any, error) {
 		a := make(fr_bw6761.Vector, n)
 		copy(a, wt)
 		return a, nil
+	case fr_grumpkin.Vector:
+		a := make(fr_grumpkin.Vector, n)
+		copy(a, wt)
+		return a, nil
 	case tinyfield.Vector:
 		a := make(tinyfield.Vector, n)
 		copy(a, wt)
@@ -86,6 +94,8 @@ func leafType(v any) reflect.Type {
 		return reflect.TypeOf(fr_bls12381.Element{})
 	case fr_bw6761.Vector:
 		return reflect.TypeOf(fr_bw6761.Element{})
+	case fr_grumpkin.Vector:
+		return reflect.TypeOf(fr_grumpkin.Element{})
 	case tinyfield.Vector:
 		return reflect.TypeOf(tinyfield.Element{})
 	case babybear.Vector:
@@ -123,6 +133,12 @@ func set(v any, index int, value any) error {
 		}
 		_, err := pv[index].SetInterface(value)
 		return err
+	case fr_grumpkin.Vector:
+		if index >= len(pv) {
+			return errors.New("out of bounds")
+		}
+		_, err := pv[index].SetInterface(value)
+		return err
 	case tinyfield.Vector:
 		if index >= len(pv) {
 			return errors.New("out of bounds")
@@ -177,6 +193,13 @@ func iterate(v any) chan any {
 			}
 			close(chValues)
 		}()
+	case fr_grumpkin.Vector:
+		go func() {
+			for i := 0; i < len(pv); i++ {
+				chValues <- &(pv)[i]
+			}
+			close(chValues)
+		}()
 	case tinyfield.Vector:
 		go func() {
 			for i := 0; i < len(pv); i++ {
@@ -214,6 +237,8 @@ func resize(v any, n int) any {
 		return make(fr_bls12381.Vector, n)
 	case fr_bw6761.Vector:
 		return make(fr_bw6761.Vector, n)
+	case fr_grumpkin.Vector:
+		return make(fr_grumpkin.Vector, n)
 	case tinyfield.Vector:
 		return make(tinyfield.Vector, n)
 	case babybear.Vector:

backend/witness/witness.go

@@ -51,6 +51,7 @@ import (
 	fr_bls12381 "github.com/consensys/gnark-crypto/ecc/bls12-381/fr"
 	fr_bn254 "github.com/consensys/gnark-crypto/ecc/bn254/fr"
 	fr_bw6761 "github.com/consensys/gnark-crypto/ecc/bw6-761/fr"
+	fr_grumpkin "github.com/consensys/gnark-crypto/ecc/grumpkin/fr"
 	"github.com/consensys/gnark-crypto/field/babybear"
 	"github.com/consensys/gnark-crypto/field/koalabear"
 	"github.com/consensys/gnark/debug"
@@ -180,6 +181,8 @@ func (w *witness) WriteTo(wr io.Writer) (n int64, err error) {
 		m, err = t.WriteTo(wr)
 	case fr_bw6761.Vector:
 		m, err = t.WriteTo(wr)
+	case fr_grumpkin.Vector:
+		m, err = t.WriteTo(wr)
 	case tinyfield.Vector:
 		m, err = t.WriteTo(wr)
 	case babybear.Vector:
@@ -220,6 +223,9 @@ func (w *witness) ReadFrom(r io.Reader) (n int64, err error) {
 	case fr_bw6761.Vector:
 		m, err = t.ReadFrom(r)
 		w.vector = t
+	case fr_grumpkin.Vector:
+		m, err = t.ReadFrom(r)
+		w.vector = t
 	case tinyfield.Vector:
 		m, err = t.ReadFrom(r)
 		w.vector = t

constraint/field.go

@@ -6,6 +6,7 @@ import (
 	"math/big"
 
 	"github.com/consensys/gnark"
+	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/internal/smallfields"
 )
 
@@ -78,6 +79,9 @@ func FitsElement[E Element](modulus *big.Int) bool {
 				return true
 			}
 		}
+		if modulus.Cmp(ecc.GRUMPKIN.ScalarField()) == 0 {
+			return true
+		}
 		return false
 	default:
 		panic("unsupported type")