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authorLibravatar Terin Stock <terinjokes@gmail.com>2025-03-09 17:47:56 +0100
committerLibravatar Terin Stock <terinjokes@gmail.com>2025-03-10 01:59:49 +0100
commit3ac1ee16f377d31a0fb80c8dae28b6239ac4229e (patch)
treef61faa581feaaeaba2542b9f2b8234a590684413 /vendor/github.com/remyoudompheng/bigfft/fft.go
parent[chore] update URLs to forked source (diff)
downloadgotosocial-3ac1ee16f377d31a0fb80c8dae28b6239ac4229e.tar.xz
[chore] remove vendor
Diffstat (limited to 'vendor/github.com/remyoudompheng/bigfft/fft.go')
-rw-r--r--vendor/github.com/remyoudompheng/bigfft/fft.go370
1 files changed, 0 insertions, 370 deletions
diff --git a/vendor/github.com/remyoudompheng/bigfft/fft.go b/vendor/github.com/remyoudompheng/bigfft/fft.go
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index 2d4c1e7a9..000000000
--- a/vendor/github.com/remyoudompheng/bigfft/fft.go
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@@ -1,370 +0,0 @@
-// Package bigfft implements multiplication of big.Int using FFT.
-//
-// The implementation is based on the Schönhage-Strassen method
-// using integer FFT modulo 2^n+1.
-package bigfft
-
-import (
- "math/big"
- "unsafe"
-)
-
-const _W = int(unsafe.Sizeof(big.Word(0)) * 8)
-
-type nat []big.Word
-
-func (n nat) String() string {
- v := new(big.Int)
- v.SetBits(n)
- return v.String()
-}
-
-// fftThreshold is the size (in words) above which FFT is used over
-// Karatsuba from math/big.
-//
-// TestCalibrate seems to indicate a threshold of 60kbits on 32-bit
-// arches and 110kbits on 64-bit arches.
-var fftThreshold = 1800
-
-// Mul computes the product x*y and returns z.
-// It can be used instead of the Mul method of
-// *big.Int from math/big package.
-func Mul(x, y *big.Int) *big.Int {
- xwords := len(x.Bits())
- ywords := len(y.Bits())
- if xwords > fftThreshold && ywords > fftThreshold {
- return mulFFT(x, y)
- }
- return new(big.Int).Mul(x, y)
-}
-
-func mulFFT(x, y *big.Int) *big.Int {
- var xb, yb nat = x.Bits(), y.Bits()
- zb := fftmul(xb, yb)
- z := new(big.Int)
- z.SetBits(zb)
- if x.Sign()*y.Sign() < 0 {
- z.Neg(z)
- }
- return z
-}
-
-// A FFT size of K=1<<k is adequate when K is about 2*sqrt(N) where
-// N = x.Bitlen() + y.Bitlen().
-
-func fftmul(x, y nat) nat {
- k, m := fftSize(x, y)
- xp := polyFromNat(x, k, m)
- yp := polyFromNat(y, k, m)
- rp := xp.Mul(&yp)
- return rp.Int()
-}
-
-// fftSizeThreshold[i] is the maximal size (in bits) where we should use
-// fft size i.
-var fftSizeThreshold = [...]int64{0, 0, 0,
- 4 << 10, 8 << 10, 16 << 10, // 5
- 32 << 10, 64 << 10, 1 << 18, 1 << 20, 3 << 20, // 10
- 8 << 20, 30 << 20, 100 << 20, 300 << 20, 600 << 20,
-}
-
-// returns the FFT length k, m the number of words per chunk
-// such that m << k is larger than the number of words
-// in x*y.
-func fftSize(x, y nat) (k uint, m int) {
- words := len(x) + len(y)
- bits := int64(words) * int64(_W)
- k = uint(len(fftSizeThreshold))
- for i := range fftSizeThreshold {
- if fftSizeThreshold[i] > bits {
- k = uint(i)
- break
- }
- }
- // The 1<<k chunks of m words must have N bits so that
- // 2^N-1 is larger than x*y. That is, m<<k > words
- m = words>>k + 1
- return
-}
-
-// valueSize returns the length (in words) to use for polynomial
-// coefficients, to compute a correct product of polynomials P*Q
-// where deg(P*Q) < K (== 1<<k) and where coefficients of P and Q are
-// less than b^m (== 1 << (m*_W)).
-// The chosen length (in bits) must be a multiple of 1 << (k-extra).
-func valueSize(k uint, m int, extra uint) int {
- // The coefficients of P*Q are less than b^(2m)*K
- // so we need W * valueSize >= 2*m*W+K
- n := 2*m*_W + int(k) // necessary bits
- K := 1 << (k - extra)
- if K < _W {
- K = _W
- }
- n = ((n / K) + 1) * K // round to a multiple of K
- return n / _W
-}
-
-// poly represents an integer via a polynomial in Z[x]/(x^K+1)
-// where K is the FFT length and b^m is the computation basis 1<<(m*_W).
-// If P = a[0] + a[1] x + ... a[n] x^(K-1), the associated natural number
-// is P(b^m).
-type poly struct {
- k uint // k is such that K = 1<<k.
- m int // the m such that P(b^m) is the original number.
- a []nat // a slice of at most K m-word coefficients.
-}
-
-// polyFromNat slices the number x into a polynomial
-// with 1<<k coefficients made of m words.
-func polyFromNat(x nat, k uint, m int) poly {
- p := poly{k: k, m: m}
- length := len(x)/m + 1
- p.a = make([]nat, length)
- for i := range p.a {
- if len(x) < m {
- p.a[i] = make(nat, m)
- copy(p.a[i], x)
- break
- }
- p.a[i] = x[:m]
- x = x[m:]
- }
- return p
-}
-
-// Int evaluates back a poly to its integer value.
-func (p *poly) Int() nat {
- length := len(p.a)*p.m + 1
- if na := len(p.a); na > 0 {
- length += len(p.a[na-1])
- }
- n := make(nat, length)
- m := p.m
- np := n
- for i := range p.a {
- l := len(p.a[i])
- c := addVV(np[:l], np[:l], p.a[i])
- if np[l] < ^big.Word(0) {
- np[l] += c
- } else {
- addVW(np[l:], np[l:], c)
- }
- np = np[m:]
- }
- n = trim(n)
- return n
-}
-
-func trim(n nat) nat {
- for i := range n {
- if n[len(n)-1-i] != 0 {
- return n[:len(n)-i]
- }
- }
- return nil
-}
-
-// Mul multiplies p and q modulo X^K-1, where K = 1<<p.k.
-// The product is done via a Fourier transform.
-func (p *poly) Mul(q *poly) poly {
- // extra=2 because:
- // * some power of 2 is a K-th root of unity when n is a multiple of K/2.
- // * 2 itself is a square (see fermat.ShiftHalf)
- n := valueSize(p.k, p.m, 2)
-
- pv, qv := p.Transform(n), q.Transform(n)
- rv := pv.Mul(&qv)
- r := rv.InvTransform()
- r.m = p.m
- return r
-}
-
-// A polValues represents the value of a poly at the powers of a
-// K-th root of unity θ=2^(l/2) in Z/(b^n+1)Z, where b^n = 2^(K/4*l).
-type polValues struct {
- k uint // k is such that K = 1<<k.
- n int // the length of coefficients, n*_W a multiple of K/4.
- values []fermat // a slice of K (n+1)-word values
-}
-
-// Transform evaluates p at θ^i for i = 0...K-1, where
-// θ is a K-th primitive root of unity in Z/(b^n+1)Z.
-func (p *poly) Transform(n int) polValues {
- k := p.k
- inputbits := make([]big.Word, (n+1)<<k)
- input := make([]fermat, 1<<k)
- // Now computed q(ω^i) for i = 0 ... K-1
- valbits := make([]big.Word, (n+1)<<k)
- values := make([]fermat, 1<<k)
- for i := range values {
- input[i] = inputbits[i*(n+1) : (i+1)*(n+1)]
- if i < len(p.a) {
- copy(input[i], p.a[i])
- }
- values[i] = fermat(valbits[i*(n+1) : (i+1)*(n+1)])
- }
- fourier(values, input, false, n, k)
- return polValues{k, n, values}
-}
-
-// InvTransform reconstructs p (modulo X^K - 1) from its
-// values at θ^i for i = 0..K-1.
-func (v *polValues) InvTransform() poly {
- k, n := v.k, v.n
-
- // Perform an inverse Fourier transform to recover p.
- pbits := make([]big.Word, (n+1)<<k)
- p := make([]fermat, 1<<k)
- for i := range p {
- p[i] = fermat(pbits[i*(n+1) : (i+1)*(n+1)])
- }
- fourier(p, v.values, true, n, k)
- // Divide by K, and untwist q to recover p.
- u := make(fermat, n+1)
- a := make([]nat, 1<<k)
- for i := range p {
- u.Shift(p[i], -int(k))
- copy(p[i], u)
- a[i] = nat(p[i])
- }
- return poly{k: k, m: 0, a: a}
-}
-
-// NTransform evaluates p at θω^i for i = 0...K-1, where
-// θ is a (2K)-th primitive root of unity in Z/(b^n+1)Z
-// and ω = θ².
-func (p *poly) NTransform(n int) polValues {
- k := p.k
- if len(p.a) >= 1<<k {
- panic("Transform: len(p.a) >= 1<<k")
- }
- // θ is represented as a shift.
- θshift := (n * _W) >> k
- // p(x) = a_0 + a_1 x + ... + a_{K-1} x^(K-1)
- // p(θx) = q(x) where
- // q(x) = a_0 + θa_1 x + ... + θ^(K-1) a_{K-1} x^(K-1)
- //
- // Twist p by θ to obtain q.
- tbits := make([]big.Word, (n+1)<<k)
- twisted := make([]fermat, 1<<k)
- src := make(fermat, n+1)
- for i := range twisted {
- twisted[i] = fermat(tbits[i*(n+1) : (i+1)*(n+1)])
- if i < len(p.a) {
- for i := range src {
- src[i] = 0
- }
- copy(src, p.a[i])
- twisted[i].Shift(src, θshift*i)
- }
- }
-
- // Now computed q(ω^i) for i = 0 ... K-1
- valbits := make([]big.Word, (n+1)<<k)
- values := make([]fermat, 1<<k)
- for i := range values {
- values[i] = fermat(valbits[i*(n+1) : (i+1)*(n+1)])
- }
- fourier(values, twisted, false, n, k)
- return polValues{k, n, values}
-}
-
-// InvTransform reconstructs a polynomial from its values at
-// roots of x^K+1. The m field of the returned polynomial
-// is unspecified.
-func (v *polValues) InvNTransform() poly {
- k := v.k
- n := v.n
- θshift := (n * _W) >> k
-
- // Perform an inverse Fourier transform to recover q.
- qbits := make([]big.Word, (n+1)<<k)
- q := make([]fermat, 1<<k)
- for i := range q {
- q[i] = fermat(qbits[i*(n+1) : (i+1)*(n+1)])
- }
- fourier(q, v.values, true, n, k)
-
- // Divide by K, and untwist q to recover p.
- u := make(fermat, n+1)
- a := make([]nat, 1<<k)
- for i := range q {
- u.Shift(q[i], -int(k)-i*θshift)
- copy(q[i], u)
- a[i] = nat(q[i])
- }
- return poly{k: k, m: 0, a: a}
-}
-
-// fourier performs an unnormalized Fourier transform
-// of src, a length 1<<k vector of numbers modulo b^n+1
-// where b = 1<<_W.
-func fourier(dst []fermat, src []fermat, backward bool, n int, k uint) {
- var rec func(dst, src []fermat, size uint)
- tmp := make(fermat, n+1) // pre-allocate temporary variables.
- tmp2 := make(fermat, n+1) // pre-allocate temporary variables.
-
- // The recursion function of the FFT.
- // The root of unity used in the transform is ω=1<<(ω2shift/2).
- // The source array may use shifted indices (i.e. the i-th
- // element is src[i << idxShift]).
- rec = func(dst, src []fermat, size uint) {
- idxShift := k - size
- ω2shift := (4 * n * _W) >> size
- if backward {
- ω2shift = -ω2shift
- }
-
- // Easy cases.
- if len(src[0]) != n+1 || len(dst[0]) != n+1 {
- panic("len(src[0]) != n+1 || len(dst[0]) != n+1")
- }
- switch size {
- case 0:
- copy(dst[0], src[0])
- return
- case 1:
- dst[0].Add(src[0], src[1<<idxShift]) // dst[0] = src[0] + src[1]
- dst[1].Sub(src[0], src[1<<idxShift]) // dst[1] = src[0] - src[1]
- return
- }
-
- // Let P(x) = src[0] + src[1<<idxShift] * x + ... + src[K-1 << idxShift] * x^(K-1)
- // The P(x) = Q1(x²) + x*Q2(x²)
- // where Q1's coefficients are src with indices shifted by 1
- // where Q2's coefficients are src[1<<idxShift:] with indices shifted by 1
-
- // Split destination vectors in halves.
- dst1 := dst[:1<<(size-1)]
- dst2 := dst[1<<(size-1):]
- // Transform Q1 and Q2 in the halves.
- rec(dst1, src, size-1)
- rec(dst2, src[1<<idxShift:], size-1)
-
- // Reconstruct P's transform from transforms of Q1 and Q2.
- // dst[i] is dst1[i] + ω^i * dst2[i]
- // dst[i + 1<<(k-1)] is dst1[i] + ω^(i+K/2) * dst2[i]
- //
- for i := range dst1 {
- tmp.ShiftHalf(dst2[i], i*ω2shift, tmp2) // ω^i * dst2[i]
- dst2[i].Sub(dst1[i], tmp)
- dst1[i].Add(dst1[i], tmp)
- }
- }
- rec(dst, src, k)
-}
-
-// Mul returns the pointwise product of p and q.
-func (p *polValues) Mul(q *polValues) (r polValues) {
- n := p.n
- r.k, r.n = p.k, p.n
- r.values = make([]fermat, len(p.values))
- bits := make([]big.Word, len(p.values)*(n+1))
- buf := make(fermat, 8*n)
- for i := range r.values {
- r.values[i] = bits[i*(n+1) : (i+1)*(n+1)]
- z := buf.Mul(p.values[i], q.values[i])
- copy(r.values[i], z)
- }
- return
-}