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package polynomial_test
import (
"testing"
"github.com/cloudflare/circl/group"
"github.com/cloudflare/circl/internal/test"
"github.com/cloudflare/circl/math/polynomial"
)
func TestPolyDegree(t *testing.T) {
g := group.P256
t.Run("zeroPoly", func(t *testing.T) {
p := polynomial.New(nil)
test.CheckOk(p.Degree() == -1, "it should be -1", t)
p = polynomial.New([]group.Scalar{})
test.CheckOk(p.Degree() == -1, "it should be -1", t)
})
t.Run("constantPoly", func(t *testing.T) {
c := []group.Scalar{
g.NewScalar().SetUint64(0),
g.NewScalar().SetUint64(0),
}
p := polynomial.New(c)
test.CheckOk(p.Degree() == 0, "it should be 0", t)
})
t.Run("linearPoly", func(t *testing.T) {
c := []group.Scalar{
g.NewScalar().SetUint64(0),
g.NewScalar().SetUint64(1),
g.NewScalar().SetUint64(0),
}
p := polynomial.New(c)
test.CheckOk(p.Degree() == 1, "it should be 1", t)
})
}
func TestPolyEval(t *testing.T) {
g := group.P256
c := []group.Scalar{
g.NewScalar(),
g.NewScalar(),
g.NewScalar(),
}
c[0].SetUint64(5)
c[1].SetUint64(5)
c[2].SetUint64(2)
p := polynomial.New(c)
x := g.NewScalar()
x.SetUint64(10)
got := p.Evaluate(x)
want := g.NewScalar()
want.SetUint64(255)
if !got.IsEqual(want) {
test.ReportError(t, got, want)
}
}
func TestLagrange(t *testing.T) {
g := group.P256
c := []group.Scalar{
g.NewScalar(),
g.NewScalar(),
g.NewScalar(),
}
c[0].SetUint64(1234)
c[1].SetUint64(166)
c[2].SetUint64(94)
p := polynomial.New(c)
x := []group.Scalar{g.NewScalar(), g.NewScalar(), g.NewScalar()}
x[0].SetUint64(2)
x[1].SetUint64(4)
x[2].SetUint64(5)
y := []group.Scalar{}
for i := range x {
y = append(y, p.Evaluate(x[i]))
}
zero := g.NewScalar()
l := polynomial.NewLagrangePolynomial(x, y)
test.CheckOk(l.Degree() == p.Degree(), "bad degree", t)
got := l.Evaluate(zero)
want := p.Evaluate(zero)
if !got.IsEqual(want) {
test.ReportError(t, got, want)
}
// Test Kronecker's delta of LagrangeBase.
// Thus:
// L_j(x[i]) = { 1, if i == j;
// { 0, otherwise.
one := g.NewScalar()
one.SetUint64(1)
for j := range x {
for i := range x {
got := polynomial.LagrangeBase(uint(j), x, x[i])
if i == j {
want = one
} else {
want = zero
}
if !got.IsEqual(want) {
test.ReportError(t, got, want)
}
}
}
// Test that inputs are different length
err := test.CheckPanic(func() { polynomial.NewLagrangePolynomial(x, y[:1]) })
test.CheckNoErr(t, err, "should panic")
// Test that nodes must be different.
x[0].Set(x[1])
err = test.CheckPanic(func() { polynomial.NewLagrangePolynomial(x, y) })
test.CheckNoErr(t, err, "should panic")
// Test LagrangeBase wrong index
err = test.CheckPanic(func() { polynomial.LagrangeBase(10, x, zero) })
test.CheckNoErr(t, err, "should panic")
}
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