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101 lines
2.0 KiB
101 lines
2.0 KiB
package prover
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import (
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"math"
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"math/big"
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)
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type rootsT struct {
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roots [][]*big.Int
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w []*big.Int
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}
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func newRootsT() rootsT {
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var roots rootsT
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rem := new(big.Int).Sub(R, big.NewInt(1))
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s := 0
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for rem.Bit(0) == 0 { // rem.Bit==0 when even
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s++
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rem = new(big.Int).Rsh(rem, 1)
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}
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roots.w = make([]*big.Int, s+1)
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roots.w[s] = fExp(big.NewInt(5), rem)
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n := s - 1
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for n >= 0 {
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roots.w[n] = fMul(roots.w[n+1], roots.w[n+1])
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n--
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}
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roots.roots = make([][]*big.Int, 50) // TODO WIP
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roots.setRoots(15)
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return roots
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}
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func (roots rootsT) setRoots(n int) {
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for i := n; i >= 0 && nil == roots.roots[i]; i-- { // TODO tmp i<=len(r)
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r := big.NewInt(1)
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nroots := 1 << i
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var rootsi []*big.Int
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for j := 0; j < nroots; j++ {
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rootsi = append(rootsi, r)
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r = fMul(r, roots.w[i])
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}
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roots.roots[i] = rootsi
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}
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}
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func fft(roots rootsT, pall []*big.Int, bits, offset, step int) []*big.Int {
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n := 1 << bits
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if n == 1 {
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return []*big.Int{pall[offset]}
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} else if n == 2 {
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return []*big.Int{
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fAdd(pall[offset], pall[offset+step]), // TODO tmp
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fSub(pall[offset], pall[offset+step]),
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}
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}
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ndiv2 := n >> 1
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p1 := fft(roots, pall, bits-1, offset, step*2)
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p2 := fft(roots, pall, bits-1, offset+step, step*2)
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// var out []*big.Int
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out := make([]*big.Int, n)
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for i := 0; i < ndiv2; i++ {
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// fmt.Println(i, len(roots.roots))
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out[i] = fAdd(p1[i], fMul(roots.roots[bits][i], p2[i]))
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out[i+ndiv2] = fSub(p1[i], fMul(roots.roots[bits][i], p2[i]))
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}
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return out
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}
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func ifft(p []*big.Int) []*big.Int {
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if len(p) <= 1 {
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return p
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}
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bits := math.Log2(float64(len(p)-1)) + 1
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roots := newRootsT()
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roots.setRoots(int(bits))
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m := 1 << int(bits)
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ep := extend(p, m)
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res := fft(roots, ep, int(bits), 0, 1)
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twoinvm := fInv(fMul(big.NewInt(1), big.NewInt(int64(m))))
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var resn []*big.Int
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for i := 0; i < m; i++ {
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resn = append(resn, fMul(res[(m-i)%m], twoinvm))
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}
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return resn
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}
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func extend(p []*big.Int, e int) []*big.Int {
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if e == len(p) {
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return p
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}
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z := arrayOfZeroes(e - len(p))
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return append(p, z...)
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}
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