github.com/consensys/gnark-crypto@v0.14.0/ecc/bls24-317/fr/generator.go (about)

     1  // Copyright 2020 Consensys Software Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Code generated by consensys/gnark-crypto DO NOT EDIT
    16  
    17  package fr
    18  
    19  import (
    20  	"fmt"
    21  	"math/big"
    22  	"math/bits"
    23  
    24  	"github.com/consensys/gnark-crypto/ecc"
    25  )
    26  
    27  // Generator returns a generator for Z/2^(log(m))Z
    28  // or an error if m is too big (required root of unity doesn't exist)
    29  func Generator(m uint64) (Element, error) {
    30  	x := ecc.NextPowerOfTwo(m)
    31  
    32  	var rootOfUnity Element
    33  
    34  	rootOfUnity.SetString("16532287748948254263922689505213135976137839535221842169193829039521719560631")
    35  	const maxOrderRoot uint64 = 60
    36  
    37  	// find generator for Z/2^(log(m))Z
    38  	logx := uint64(bits.TrailingZeros64(x))
    39  	if logx > maxOrderRoot {
    40  		return Element{}, fmt.Errorf("m (%d) is too big: the required root of unity does not exist", m)
    41  	}
    42  
    43  	expo := uint64(1 << (maxOrderRoot - logx))
    44  	var generator Element
    45  	generator.Exp(rootOfUnity, big.NewInt(int64(expo))) // order x
    46  	return generator, nil
    47  }