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solver_test.go
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solver_test.go
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package test
import (
"fmt"
"io"
"math/big"
"reflect"
"strconv"
"strings"
"testing"
"github.com/consensys/gnark/backend/witness"
"github.com/consensys/gnark/constraint"
"github.com/consensys/gnark/constraint/solver"
"github.com/consensys/gnark/debug"
"github.com/consensys/gnark/frontend"
"github.com/consensys/gnark/frontend/cs/r1cs"
"github.com/consensys/gnark/frontend/cs/scs"
"github.com/consensys/gnark/frontend/schema"
"github.com/consensys/gnark/internal/backend/circuits"
"github.com/consensys/gnark/internal/kvstore"
"github.com/consensys/gnark/internal/tinyfield"
"github.com/consensys/gnark/internal/utils"
)
// ignore witness size larger than this bound
const permutterBound = 3
// r1cs + sparser1cs
const nbSystems = 2
var builders [2]frontend.NewBuilder
func TestSolverConsistency(t *testing.T) {
if testing.Short() {
t.Skip("skipping R1CS solver test with testing.Short() flag set")
return
}
// idea is test circuits, we are going to test all possible values of the witness.
// (hence the choice of a small modulus for the field size)
//
// we generate witnesses and compare with the output of big.Int test engine against
// R1CS and SparseR1CS solvers
for name := range circuits.Circuits {
t.Run(name, func(t *testing.T) {
tc := circuits.Circuits[name]
t.Parallel()
err := consistentSolver(tc.Circuit, tc.HintFunctions)
if err != nil {
t.Fatal(err)
}
})
}
}
// witness used for the permutter. It implements the Witness interface
// using mock methods (only the underlying vector is required).
type permutterWitness struct {
vector any
}
func (pw *permutterWitness) WriteTo(w io.Writer) (int64, error) {
return 0, nil
}
func (pw *permutterWitness) ReadFrom(r io.Reader) (int64, error) {
return 0, nil
}
func (pw *permutterWitness) MarshalBinary() ([]byte, error) {
return nil, nil
}
func (pw *permutterWitness) UnmarshalBinary([]byte) error {
return nil
}
func (pw *permutterWitness) Public() (witness.Witness, error) {
return pw, nil
}
func (pw *permutterWitness) Vector() any {
return pw.vector
}
func (pw *permutterWitness) ToJSON(s *schema.Schema) ([]byte, error) {
return nil, nil
}
func (pw *permutterWitness) FromJSON(s *schema.Schema, data []byte) error {
return nil
}
func (pw *permutterWitness) Fill(nbPublic, nbSecret int, values <-chan any) error {
return nil
}
func newPermutterWitness(pv tinyfield.Vector) witness.Witness {
return &permutterWitness{
vector: pv,
}
}
type permutter struct {
circuit frontend.Circuit
constraintSystems [2]constraint.ConstraintSystem
witness []tinyfield.Element
hints []solver.Hint
}
// note that circuit will be mutated and this is not thread safe
func (p *permutter) permuteAndTest(index int) error {
for i := 0; i < len(tinyfieldElements); i++ {
p.witness[index].SetUint64(tinyfieldElements[i])
if index == len(p.witness)-1 {
// we have a unique permutation
var errorSystems [2]error
var errorEngines [2]error
// 2 constraints systems
for k := 0; k < nbSystems; k++ {
errorSystems[k] = p.solve(k)
// solve the cs using test engine
// first copy the witness in the circuit
copyWitnessFromVector(p.circuit, p.witness)
errorEngines[0] = isSolvedEngine(p.circuit, tinyfield.Modulus())
copyWitnessFromVector(p.circuit, p.witness)
errorEngines[1] = isSolvedEngine(p.circuit, tinyfield.Modulus(), SetAllVariablesAsConstants())
}
if (errorSystems[0] == nil) != (errorEngines[0] == nil) ||
(errorSystems[1] == nil) != (errorEngines[0] == nil) ||
(errorEngines[0] == nil) != (errorEngines[1] == nil) {
return fmt.Errorf("errSCS :%s\nerrR1CS :%s\nerrEngine(const=false): %s\nerrEngine(const=true): %s\nwitness: %s",
formatError(errorSystems[0]),
formatError(errorSystems[1]),
formatError(errorEngines[0]),
formatError(errorEngines[1]),
formatWitness(p.witness))
}
} else {
// recurse
if err := p.permuteAndTest(index + 1); err != nil {
return err
}
}
}
return nil
}
func formatError(err error) string {
if err == nil {
return "<nil>"
}
return err.Error()
}
func formatWitness(witness []tinyfield.Element) string {
var sbb strings.Builder
sbb.WriteByte('[')
for i := 0; i < len(witness); i++ {
sbb.WriteString(strconv.Itoa(int(witness[i].Uint64())))
if i != len(witness)-1 {
sbb.WriteString(", ")
}
}
sbb.WriteByte(']')
return sbb.String()
}
func (p *permutter) solve(i int) error {
pw := newPermutterWitness(p.witness)
_, err := p.constraintSystems[i].Solve(pw, solver.WithHints(p.hints...))
return err
}
// isSolvedEngine behaves like test.IsSolved except it doesn't clone the circuit
func isSolvedEngine(c frontend.Circuit, field *big.Int, opts ...TestEngineOption) (err error) {
e := &engine{
curveID: utils.FieldToCurve(field),
q: new(big.Int).Set(field),
constVars: false,
Store: kvstore.New(),
}
for _, opt := range opts {
if err := opt(e); err != nil {
return fmt.Errorf("apply option: %w", err)
}
}
defer func() {
if r := recover(); r != nil {
err = fmt.Errorf("%v\n%s", r, string(debug.Stack()))
}
}()
if err = c.Define(e); err != nil {
return fmt.Errorf("define: %w", err)
}
if err = callDeferred(e); err != nil {
return fmt.Errorf("")
}
return
}
// fill the "to" frontend.Circuit with values from the provided vector
// values are assumed to be ordered [public | secret]
func copyWitnessFromVector(to frontend.Circuit, from []tinyfield.Element) {
i := 0
schema.Walk(to, tVariable, func(f schema.LeafInfo, tInput reflect.Value) error {
if f.Visibility == schema.Public {
tInput.Set(reflect.ValueOf(from[i]))
i++
}
return nil
})
schema.Walk(to, tVariable, func(f schema.LeafInfo, tInput reflect.Value) error {
if f.Visibility == schema.Secret {
tInput.Set(reflect.ValueOf(from[i]))
i++
}
return nil
})
}
// ConsistentSolver solves given circuit with all possible witness combinations using internal/tinyfield
//
// Since the goal of this method is to flag potential solver issues, it is not exposed as an API for now
func consistentSolver(circuit frontend.Circuit, hintFunctions []solver.Hint) error {
p := permutter{
circuit: circuit,
hints: hintFunctions,
}
// compile the systems
for i := 0; i < nbSystems; i++ {
ccs, err := frontend.Compile(tinyfield.Modulus(), builders[i], circuit)
if err != nil {
return err
}
p.constraintSystems[i] = ccs
if i == 0 { // the -1 is only for r1cs...
n := ccs.GetNbPublicVariables() - 1 + ccs.GetNbSecretVariables()
if n > permutterBound {
return nil
}
p.witness = make([]tinyfield.Element, n)
}
}
return p.permuteAndTest(0)
}
// [0, 1, ..., q - 1], with q == tinyfield.Modulus()
var tinyfieldElements []uint64
func init() {
n := tinyfield.Modulus().Uint64()
tinyfieldElements = make([]uint64, n)
for i := uint64(0); i < n; i++ {
tinyfieldElements[i] = i
}
builders[0] = r1cs.NewBuilder
builders[1] = scs.NewBuilder
}