github.com/aigarnetwork/aigar@v0.0.0-20191115204914-d59a6eb70f8e/crypto/bn256/cloudflare/gfp.go (about)

     1  //  Copyright 2018 The go-ethereum Authors
     2  //  Copyright 2019 The go-aigar Authors
     3  //  This file is part of the go-aigar library.
     4  //
     5  //  The go-aigar library is free software: you can redistribute it and/or modify
     6  //  it under the terms of the GNU Lesser General Public License as published by
     7  //  the Free Software Foundation, either version 3 of the License, or
     8  //  (at your option) any later version.
     9  //
    10  //  The go-aigar library is distributed in the hope that it will be useful,
    11  //  but WITHOUT ANY WARRANTY; without even the implied warranty of
    12  //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    13  //  GNU Lesser General Public License for more details.
    14  //
    15  //  You should have received a copy of the GNU Lesser General Public License
    16  //  along with the go-aigar library. If not, see <http://www.gnu.org/licenses/>.
    17  
    18  package bn256
    19  
    20  import (
    21  	"errors"
    22  	"fmt"
    23  )
    24  
    25  type gfP [4]uint64
    26  
    27  func newGFp(x int64) (out *gfP) {
    28  	if x >= 0 {
    29  		out = &gfP{uint64(x)}
    30  	} else {
    31  		out = &gfP{uint64(-x)}
    32  		gfpNeg(out, out)
    33  	}
    34  
    35  	montEncode(out, out)
    36  	return out
    37  }
    38  
    39  func (e *gfP) String() string {
    40  	return fmt.Sprintf("%16.16x%16.16x%16.16x%16.16x", e[3], e[2], e[1], e[0])
    41  }
    42  
    43  func (e *gfP) Set(f *gfP) {
    44  	e[0] = f[0]
    45  	e[1] = f[1]
    46  	e[2] = f[2]
    47  	e[3] = f[3]
    48  }
    49  
    50  func (e *gfP) Invert(f *gfP) {
    51  	bits := [4]uint64{0x3c208c16d87cfd45, 0x97816a916871ca8d, 0xb85045b68181585d, 0x30644e72e131a029}
    52  
    53  	sum, power := &gfP{}, &gfP{}
    54  	sum.Set(rN1)
    55  	power.Set(f)
    56  
    57  	for word := 0; word < 4; word++ {
    58  		for bit := uint(0); bit < 64; bit++ {
    59  			if (bits[word]>>bit)&1 == 1 {
    60  				gfpMul(sum, sum, power)
    61  			}
    62  			gfpMul(power, power, power)
    63  		}
    64  	}
    65  
    66  	gfpMul(sum, sum, r3)
    67  	e.Set(sum)
    68  }
    69  
    70  func (e *gfP) Marshal(out []byte) {
    71  	for w := uint(0); w < 4; w++ {
    72  		for b := uint(0); b < 8; b++ {
    73  			out[8*w+b] = byte(e[3-w] >> (56 - 8*b))
    74  		}
    75  	}
    76  }
    77  
    78  func (e *gfP) Unmarshal(in []byte) error {
    79  	// Unmarshal the bytes into little endian form
    80  	for w := uint(0); w < 4; w++ {
    81  		for b := uint(0); b < 8; b++ {
    82  			e[3-w] += uint64(in[8*w+b]) << (56 - 8*b)
    83  		}
    84  	}
    85  	// Ensure the point respects the curve modulus
    86  	for i := 3; i >= 0; i-- {
    87  		if e[i] < p2[i] {
    88  			return nil
    89  		}
    90  		if e[i] > p2[i] {
    91  			return errors.New("bn256: coordinate exceeds modulus")
    92  		}
    93  	}
    94  	return errors.New("bn256: coordinate equals modulus")
    95  }
    96  
    97  func montEncode(c, a *gfP) { gfpMul(c, a, r2) }
    98  func montDecode(c, a *gfP) { gfpMul(c, a, &gfP{1}) }