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univariate.go
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univariate.go
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package polynomial
import (
"fmt"
"github.com/AlexandreBelling/gnark/frontend"
"github.com/consensys/gnark-crypto/ecc/bn254/fr"
)
// Univariate encodes a univariate polynomial: a0 + a1X + ... + ad X^d <=> {a0, a1, ... , ad}
type Univariate []frontend.Variable
// NewUnivariate is the default constructor
func NewUnivariate(coeffs []frontend.Variable) Univariate {
return coeffs
}
// AllocateUnivariate returns an empty multilinear with a given size
func AllocateUnivariate(degree int) Univariate {
return NewUnivariate(make([]frontend.Variable, degree+1))
}
// Assign value to a previously allocated univariate
func (u Univariate) Assign(coeffs []fr.Element) {
if len(coeffs) != len(u) {
panic(fmt.Sprintf("Inconsistent assignment for univariate poly %v != %v", len(coeffs), len(u)))
}
for i, c := range coeffs {
u[i] = c
}
}
// Eval returns p(x)
func (u Univariate) Eval(cs frontend.API, x frontend.Variable) (res frontend.Variable) {
res = frontend.Variable(0)
aux := frontend.Variable(0)
for i := len(u) - 1; i >= 0; i-- {
if i != len(u)-1 {
res = cs.Mul(aux, x)
}
aux = cs.Add(res, u[i])
}
// TODO why mul by 1 ?
return cs.Mul(aux, 1)
}
// ZeroAndOne returns p(0) + p(1)
func (u Univariate) ZeroAndOne(cs frontend.API) frontend.Variable {
res := cs.Add(u[0], u[0], u[1:]...)
return res
}