mirror of
https://github.com/octoleo/syncthing.git
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281 lines
6.6 KiB
Go
281 lines
6.6 KiB
Go
/*
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Reed-Solomon Codes over GF(2^8)
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Primitive Polynomial: x^8+x^4+x^3+x^2+1
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Galois Filed arithmetic using Intel SIMD instructions (AVX2 or SSSE3)
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*/
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package reedsolomon
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import "errors"
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// Encoder implements for Reed-Solomon Encoding/Reconstructing
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type Encoder interface {
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// Encode multiply generator-matrix with data
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// len(vects) must be equal with num of data+parity
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Encode(vects [][]byte) error
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// Result of reconst will be put into origin position of vects
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// it means if you lost vects[0], after reconst the vects[0]'s data will be back in vects[0]
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// Reconstruct repair lost data & parity
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// Set vect nil if lost
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Reconstruct(vects [][]byte) error
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// Reconstruct repair lost data
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// Set vect nil if lost
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ReconstructData(vects [][]byte) error
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// ReconstWithPos repair lost data&parity with has&lost vects position
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// Save bandwidth&disk I/O (cmp with Reconstruct, if the lost is less than num of parity)
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// As erasure codes, we must know which vect is broken,
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// so it's necessary to provide such APIs
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// len(has) must equal num of data vects
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// Example:
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// in 3+2, the whole position: [0,1,2,3,4]
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// if lost vects[0]
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// the "has" could be [1,2,3] or [1,2,4] or ...
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// then you must be sure that vects[1] vects[2] vects[3] have correct data (if the "has" is [1,2,3])
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// the "dLost" will be [0]
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// ps:
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// 1. the above lists are in increasing orders TODO support out-of-order
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// 2. each vect has same len, don't set it nil
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// so we don't need to make slice
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ReconstWithPos(vects [][]byte, has, dLost, pLost []int) error
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//// ReconstWithPos repair lost data with survived&lost vects position
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//// Don't need to append position of parity lost into "lost"
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ReconstDataWithPos(vects [][]byte, has, dLost []int) error
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}
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func checkCfg(d, p int) error {
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if (d <= 0) || (p <= 0) {
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return errors.New("rs.New: data or parity <= 0")
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}
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if d+p >= 256 {
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return errors.New("rs.New: data+parity >= 256")
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}
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return nil
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}
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// New create an Encoder (vandermonde matrix as Encoding matrix)
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func New(data, parity int) (enc Encoder, err error) {
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err = checkCfg(data, parity)
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if err != nil {
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return
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}
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e, err := genEncMatrixVand(data, parity)
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if err != nil {
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return
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}
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return newRS(data, parity, e), nil
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}
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// NewCauchy create an Encoder (cauchy matrix as Generator Matrix)
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func NewCauchy(data, parity int) (enc Encoder, err error) {
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err = checkCfg(data, parity)
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if err != nil {
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return
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}
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e := genEncMatrixCauchy(data, parity)
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return newRS(data, parity, e), nil
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}
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type encBase struct {
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data int
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parity int
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encode []byte
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gen []byte
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}
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func checkEnc(d, p int, vs [][]byte) (size int, err error) {
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total := len(vs)
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if d+p != total {
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err = errors.New("rs.checkER: vects not match rs args")
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return
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}
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size = len(vs[0])
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if size == 0 {
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err = errors.New("rs.checkER: vects size = 0")
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return
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}
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for i := 1; i < total; i++ {
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if len(vs[i]) != size {
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err = errors.New("rs.checkER: vects size mismatch")
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return
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}
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}
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return
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}
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func (e *encBase) Encode(vects [][]byte) (err error) {
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d := e.data
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p := e.parity
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_, err = checkEnc(d, p, vects)
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if err != nil {
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return
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}
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dv := vects[:d]
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pv := vects[d:]
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g := e.gen
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for i := 0; i < d; i++ {
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for j := 0; j < p; j++ {
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if i != 0 {
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mulVectAdd(g[j*d+i], dv[i], pv[j])
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} else {
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mulVect(g[j*d], dv[0], pv[j])
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}
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}
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}
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return
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}
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func mulVect(c byte, a, b []byte) {
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t := mulTbl[c]
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for i := 0; i < len(a); i++ {
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b[i] = t[a[i]]
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}
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}
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func mulVectAdd(c byte, a, b []byte) {
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t := mulTbl[c]
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for i := 0; i < len(a); i++ {
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b[i] ^= t[a[i]]
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}
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}
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func (e *encBase) Reconstruct(vects [][]byte) (err error) {
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return e.reconstruct(vects, false)
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}
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func (e *encBase) ReconstructData(vects [][]byte) (err error) {
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return e.reconstruct(vects, true)
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}
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func (e *encBase) ReconstWithPos(vects [][]byte, has, dLost, pLost []int) error {
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return e.reconstWithPos(vects, has, dLost, pLost, false)
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}
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func (e *encBase) ReconstDataWithPos(vects [][]byte, has, dLost []int) error {
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return e.reconstWithPos(vects, has, dLost, nil, true)
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}
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func (e *encBase) reconst(vects [][]byte, has, dLost, pLost []int, dataOnly bool) (err error) {
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d := e.data
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em := e.encode
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dCnt := len(dLost)
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size := len(vects[has[0]])
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if dCnt != 0 {
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vtmp := make([][]byte, d+dCnt)
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for i, p := range has {
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vtmp[i] = vects[p]
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}
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for i, p := range dLost {
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if len(vects[p]) == 0 {
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vects[p] = make([]byte, size)
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}
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vtmp[i+d] = vects[p]
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}
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matrixbuf := make([]byte, 4*d*d+dCnt*d)
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m := matrixbuf[:d*d]
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for i, l := range has {
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copy(m[i*d:i*d+d], em[l*d:l*d+d])
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}
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raw := matrixbuf[d*d : 3*d*d]
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im := matrixbuf[3*d*d : 4*d*d]
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err2 := matrix(m).invert(raw, d, im)
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if err2 != nil {
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return err2
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}
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g := matrixbuf[4*d*d:]
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for i, l := range dLost {
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copy(g[i*d:i*d+d], im[l*d:l*d+d])
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}
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etmp := &encBase{data: d, parity: dCnt, gen: g}
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err2 = etmp.Encode(vtmp[:d+dCnt])
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if err2 != nil {
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return err2
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}
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}
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if dataOnly {
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return
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}
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pCnt := len(pLost)
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if pCnt != 0 {
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vtmp := make([][]byte, d+pCnt)
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g := make([]byte, pCnt*d)
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for i, l := range pLost {
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copy(g[i*d:i*d+d], em[l*d:l*d+d])
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}
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for i := 0; i < d; i++ {
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vtmp[i] = vects[i]
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}
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for i, p := range pLost {
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if len(vects[p]) == 0 {
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vects[p] = make([]byte, size)
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}
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vtmp[i+d] = vects[p]
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}
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etmp := &encBase{data: d, parity: pCnt, gen: g}
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err2 := etmp.Encode(vtmp[:d+pCnt])
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if err2 != nil {
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return err2
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}
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}
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return
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}
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func (e *encBase) reconstWithPos(vects [][]byte, has, dLost, pLost []int, dataOnly bool) (err error) {
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d := e.data
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p := e.parity
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// TODO check more, maybe element in has show in lost & deal with len(has) > d
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if len(has) != d {
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return errors.New("rs.Reconst: not enough vects")
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}
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dCnt := len(dLost)
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if dCnt > p {
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return errors.New("rs.Reconst: not enough vects")
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}
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pCnt := len(pLost)
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if pCnt > p {
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return errors.New("rs.Reconst: not enough vects")
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}
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return e.reconst(vects, has, dLost, pLost, dataOnly)
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}
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func (e *encBase) reconstruct(vects [][]byte, dataOnly bool) (err error) {
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d := e.data
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p := e.parity
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t := d + p
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listBuf := make([]int, t+p)
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has := listBuf[:d]
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dLost := listBuf[d:t]
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pLost := listBuf[t : t+p]
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hasCnt, dCnt, pCnt := 0, 0, 0
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for i := 0; i < t; i++ {
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if vects[i] != nil {
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if hasCnt < d {
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has[hasCnt] = i
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hasCnt++
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}
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} else {
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if i < d {
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if dCnt < p {
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dLost[dCnt] = i
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dCnt++
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} else {
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return errors.New("rs.Reconst: not enough vects")
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}
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} else {
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if pCnt < p {
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pLost[pCnt] = i
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pCnt++
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} else {
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return errors.New("rs.Reconst: not enough vects")
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}
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}
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}
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}
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if hasCnt != d {
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return errors.New("rs.Reconst: not enough vects")
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}
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dLost = dLost[:dCnt]
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pLost = pLost[:pCnt]
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return e.reconst(vects, has, dLost, pLost, dataOnly)
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}
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