go-circom-prover-verifier/prover/gextra.go

package prover

import (
        "math/big"
	bn256 "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
	cryptoConstants "github.com/iden3/go-iden3-crypto/constants"
)

type TableG1 struct{
   data []*bn256.G1
}

func (t TableG1) GetData() []*bn256.G1 {
  return t.data
}


// Compute table of gsize elements as ::
//  Table[0] = Inf
//  Table[1] = a[0]
//  Table[2] = a[1]
//  Table[3] = a[0]+a[1]
//  .....
//  Table[(1<<gsize)-1] = a[0]+a[1]+...+a[gsize-1]
func (t *TableG1) NewTableG1(a []*bn256.G1, gsize int){
   // EC table
   table := make([]*bn256.G1, 0)

   // We need at least gsize elements. If not enough, fill with 0
   a_ext := make([]*bn256.G1, 0)
   a_ext = append(a_ext, a...)

   for i:=len(a); i<gsize; i++ {
      a_ext = append(a_ext,new(bn256.G1).ScalarBaseMult(big.NewInt(0)))
   }

   elG1 := new(bn256.G1).ScalarBaseMult(big.NewInt(0))
   table = append(table,elG1)
   last_pow2 := 1
   nelems := 0
   for i :=1; i< 1<<gsize; i++ {
      elG1 := new(bn256.G1)
      // if power of 2
      if i & (i-1) == 0{
        last_pow2 = i
        elG1.Set(a_ext[nelems])
        nelems++
      } else {
        elG1.Add(table[last_pow2], table[i-last_pow2])
        // TODO bn256 doesn't export MakeAffine function. We need to fork repo
        //table[i].MakeAffine()
      }
      table = append(table, elG1)
  }
  t.data = table
}

// Multiply scalar by precomputed table of G1 elements
func (t *TableG1) MulTableG1(k []*big.Int, gsize int) *bn256.G1 {
   // We need at least gsize elements. If not enough, fill with 0
   k_ext := make([]*big.Int, 0)
   k_ext = append(k_ext, k...)

   for i:=len(k); i < gsize; i++ {
      k_ext = append(k_ext,new(big.Int).SetUint64(0))
   }

   Q := new(bn256.G1).ScalarBaseMult(big.NewInt(0))

   msb := getMsb(k_ext)

   for i := msb-1; i >= 0; i-- {
        // TODO. bn256 doesn't export double operation. We will need to fork repo and export it
	Q = new(bn256.G1).Add(Q,Q)
        b := getBit(k_ext,i)
	if b != 0 {
          // TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
	  Q.Add(Q, t.data[b])
	} 
   }
   return Q
}

// Multiply scalar by precomputed table of G1 elements without intermediate doubling
func MulTableNoDoubleG1(t []TableG1, k []*big.Int, gsize int) *bn256.G1 {
   // We need at least gsize elements. If not enough, fill with 0
   min_nelems := len(t) * gsize
   k_ext := make([]*big.Int, 0)
   k_ext = append(k_ext, k...)
   for i := len(k); i <  min_nelems; i++ {
      k_ext = append(k_ext,new(big.Int).SetUint64(0))
   }
   // Init Adders
   nbitsQ := cryptoConstants.Q.BitLen()
   Q := make([]*bn256.G1,nbitsQ)

   for i:=0; i< nbitsQ; i++ {
     Q[i] = new(bn256.G1).ScalarBaseMult(big.NewInt(0))
   }

   // Perform bitwise addition
   for j:=0; j < len(t); j++ {
     msb := getMsb(k_ext[j*gsize:(j+1)*gsize])

     for i := msb-1; i >= 0; i-- {
        b := getBit(k_ext[j*gsize:(j+1)*gsize],i)
	if b != 0 {
          // TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
	  Q[i].Add(Q[i], t[j].data[b])
	} 
     }
   }

   // Consolidate Addition
   R := new(bn256.G1).Set(Q[nbitsQ-1])
   for i:=nbitsQ-1; i>0; i-- {
      // TODO. bn256 doesn't export double operation. We will need to fork repo and export it
      R = new(bn256.G1).Add(R,R)
      R.Add(R,Q[i-1])
   }
   return R
}

// Compute tables within function. This solution should still be faster than std  multiplication
// for gsize = 7
func ScalarMult(a []*bn256.G1, k []*big.Int, gsize int) *bn256.G1 {
     ntables := int((len(a) + gsize - 1) / gsize)
     table := TableG1{}
     Q:= new(bn256.G1).ScalarBaseMult(new(big.Int))

     for i:=0; i<ntables-1; i++ {
       table.NewTableG1( a[i*gsize:(i+1)*gsize], gsize)
       Q.Add(Q,table.MulTableG1(k[i*gsize:(i+1)*gsize], gsize))
     }
     table.NewTableG1( a[(ntables-1)*gsize:], gsize)
     Q.Add(Q,table.MulTableG1(k[(ntables-1)*gsize:], gsize))

     return Q
}

// Multiply scalar by precomputed table of G1 elements without intermediate doubling
func ScalarMultNoDoubleG1(a []*bn256.G1, k []*big.Int, gsize int) *bn256.G1 {
   ntables := int((len(a) + gsize - 1) / gsize)
   table := TableG1{}

   // We need at least gsize elements. If not enough, fill with 0
   min_nelems := ntables * gsize
   k_ext := make([]*big.Int, 0)
   k_ext = append(k_ext, k...)
   for i := len(k); i <  min_nelems; i++ {
      k_ext = append(k_ext,new(big.Int).SetUint64(0))
   }
   // Init Adders
   nbitsQ := cryptoConstants.Q.BitLen()
   Q := make([]*bn256.G1,nbitsQ)

   for i:=0; i< nbitsQ; i++ {
     Q[i] = new(bn256.G1).ScalarBaseMult(big.NewInt(0))
   }

   // Perform bitwise addition
   for j:=0; j < ntables-1; j++ {
     table.NewTableG1( a[j*gsize:(j+1)*gsize], gsize)
     msb := getMsb(k_ext[j*gsize:(j+1)*gsize])

     for i := msb-1; i >= 0; i-- {
        b := getBit(k_ext[j*gsize:(j+1)*gsize],i)
	if b != 0 {
          // TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
	  Q[i].Add(Q[i], table.data[b])
	} 
     }
   }
   table.NewTableG1( a[(ntables-1)*gsize:], gsize)
   msb := getMsb(k_ext[(ntables-1)*gsize:])

   for i := msb-1; i >= 0; i-- {
     b := getBit(k_ext[(ntables-1)*gsize:],i)
     if b != 0 {
         // TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
         Q[i].Add(Q[i], table.data[b])
     } 
   }

   // Consolidate Addition
   R := new(bn256.G1).Set(Q[nbitsQ-1])
   for i:=nbitsQ-1; i>0; i-- {
      // TODO. bn256 doesn't export double operation. We will need to fork repo and export it
      R = new(bn256.G1).Add(R,R)
      R.Add(R,Q[i-1])
   }
   return R
}

// Return most significant bit position in a group of Big Integers
func getMsb(k []*big.Int) int{
  msb := 0

  for _, el := range(k){
     tmp_msb := el.BitLen()
     if tmp_msb > msb {
        msb = tmp_msb
     }
  }
  return msb
}

// Return ith bit in group of Big Integers
func getBit(k []*big.Int, i int) uint {
   table_idx := uint(0)

   for idx, el := range(k){
     b := el.Bit(i)
     table_idx += (b << idx)
   }
   return table_idx
}