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408 lines
7.0 KiB

package binarydist
import (
"bytes"
"encoding/binary"
"io"
"io/ioutil"
)
func swap(a []int, i, j int) { a[i], a[j] = a[j], a[i] }
func split(I, V []int, start, length, h int) {
var i, j, k, x, jj, kk int
if length < 16 {
for k = start; k < start+length; k += j {
j = 1
x = V[I[k]+h]
for i = 1; k+i < start+length; i++ {
if V[I[k+i]+h] < x {
x = V[I[k+i]+h]
j = 0
}
if V[I[k+i]+h] == x {
swap(I, k+i, k+j)
j++
}
}
for i = 0; i < j; i++ {
V[I[k+i]] = k + j - 1
}
if j == 1 {
I[k] = -1
}
}
return
}
x = V[I[start+length/2]+h]
jj = 0
kk = 0
for i = start; i < start+length; i++ {
if V[I[i]+h] < x {
jj++
}
if V[I[i]+h] == x {
kk++
}
}
jj += start
kk += jj
i = start
j = 0
k = 0
for i < jj {
if V[I[i]+h] < x {
i++
} else if V[I[i]+h] == x {
swap(I, i, jj+j)
j++
} else {
swap(I, i, kk+k)
k++
}
}
for jj+j < kk {
if V[I[jj+j]+h] == x {
j++
} else {
swap(I, jj+j, kk+k)
k++
}
}
if jj > start {
split(I, V, start, jj-start, h)
}
for i = 0; i < kk-jj; i++ {
V[I[jj+i]] = kk - 1
}
if jj == kk-1 {
I[jj] = -1
}
if start+length > kk {
split(I, V, kk, start+length-kk, h)
}
}
func qsufsort(obuf []byte) []int {
var buckets [256]int
var i, h int
I := make([]int, len(obuf)+1)
V := make([]int, len(obuf)+1)
for _, c := range obuf {
buckets[c]++
}
for i = 1; i < 256; i++ {
buckets[i] += buckets[i-1]
}
copy(buckets[1:], buckets[:])
buckets[0] = 0
for i, c := range obuf {
buckets[c]++
I[buckets[c]] = i
}
I[0] = len(obuf)
for i, c := range obuf {
V[i] = buckets[c]
}
V[len(obuf)] = 0
for i = 1; i < 256; i++ {
if buckets[i] == buckets[i-1]+1 {
I[buckets[i]] = -1
}
}
I[0] = -1
for h = 1; I[0] != -(len(obuf) + 1); h += h {
var n int
for i = 0; i < len(obuf)+1; {
if I[i] < 0 {
n -= I[i]
i -= I[i]
} else {
if n != 0 {
I[i-n] = -n
}
n = V[I[i]] + 1 - i
split(I, V, i, n, h)
i += n
n = 0
}
}
if n != 0 {
I[i-n] = -n
}
}
for i = 0; i < len(obuf)+1; i++ {
I[V[i]] = i
}
return I
}
func matchlen(a, b []byte) (i int) {
for i < len(a) && i < len(b) && a[i] == b[i] {
i++
}
return i
}
func search(I []int, obuf, nbuf []byte, st, en int) (pos, n int) {
if en-st < 2 {
x := matchlen(obuf[I[st]:], nbuf)
y := matchlen(obuf[I[en]:], nbuf)
if x > y {
return I[st], x
} else {
return I[en], y
}
}
x := st + (en-st)/2
if bytes.Compare(obuf[I[x]:], nbuf) < 0 {
return search(I, obuf, nbuf, x, en)
} else {
return search(I, obuf, nbuf, st, x)
}
panic("unreached")
}
// Diff computes the difference between old and new, according to the bsdiff
// algorithm, and writes the result to patch.
func Diff(old, new io.Reader, patch io.Writer) error {
obuf, err := ioutil.ReadAll(old)
if err != nil {
return err
}
nbuf, err := ioutil.ReadAll(new)
if err != nil {
return err
}
pbuf, err := diffBytes(obuf, nbuf)
if err != nil {
return err
}
_, err = patch.Write(pbuf)
return err
}
func diffBytes(obuf, nbuf []byte) ([]byte, error) {
var patch seekBuffer
err := diff(obuf, nbuf, &patch)
if err != nil {
return nil, err
}
return patch.buf, nil
}
func diff(obuf, nbuf []byte, patch io.WriteSeeker) error {
var lenf int
I := qsufsort(obuf)
db := make([]byte, len(nbuf))
eb := make([]byte, len(nbuf))
var dblen, eblen int
var hdr header
hdr.Magic = magic
hdr.NewSize = int64(len(nbuf))
err := binary.Write(patch, signMagLittleEndian{}, &hdr)
if err != nil {
return err
}
// Compute the differences, writing ctrl as we go
pfbz2, err := newBzip2Writer(patch)
if err != nil {
return err
}
var scan, pos, length int
var lastscan, lastpos, lastoffset int
for scan < len(nbuf) {
var oldscore int
scan += length
for scsc := scan; scan < len(nbuf); scan++ {
pos, length = search(I, obuf, nbuf[scan:], 0, len(obuf))
for ; scsc < scan+length; scsc++ {
if scsc+lastoffset < len(obuf) &&
obuf[scsc+lastoffset] == nbuf[scsc] {
oldscore++
}
}
if (length == oldscore && length != 0) || length > oldscore+8 {
break
}
if scan+lastoffset < len(obuf) && obuf[scan+lastoffset] == nbuf[scan] {
oldscore--
}
}
if length != oldscore || scan == len(nbuf) {
var s, Sf int
lenf = 0
for i := 0; lastscan+i < scan && lastpos+i < len(obuf); {
if obuf[lastpos+i] == nbuf[lastscan+i] {
s++
}
i++
if s*2-i > Sf*2-lenf {
Sf = s
lenf = i
}
}
lenb := 0
if scan < len(nbuf) {
var s, Sb int
for i := 1; (scan >= lastscan+i) && (pos >= i); i++ {
if obuf[pos-i] == nbuf[scan-i] {
s++
}
if s*2-i > Sb*2-lenb {
Sb = s
lenb = i
}
}
}
if lastscan+lenf > scan-lenb {
overlap := (lastscan + lenf) - (scan - lenb)
s := 0
Ss := 0
lens := 0
for i := 0; i < overlap; i++ {
if nbuf[lastscan+lenf-overlap+i] == obuf[lastpos+lenf-overlap+i] {
s++
}
if nbuf[scan-lenb+i] == obuf[pos-lenb+i] {
s--
}
if s > Ss {
Ss = s
lens = i + 1
}
}
lenf += lens - overlap
lenb -= lens
}
for i := 0; i < lenf; i++ {
db[dblen+i] = nbuf[lastscan+i] - obuf[lastpos+i]
}
for i := 0; i < (scan-lenb)-(lastscan+lenf); i++ {
eb[eblen+i] = nbuf[lastscan+lenf+i]
}
dblen += lenf
eblen += (scan - lenb) - (lastscan + lenf)
err = binary.Write(pfbz2, signMagLittleEndian{}, int64(lenf))
if err != nil {
pfbz2.Close()
return err
}
val := (scan - lenb) - (lastscan + lenf)
err = binary.Write(pfbz2, signMagLittleEndian{}, int64(val))
if err != nil {
pfbz2.Close()
return err
}
val = (pos - lenb) - (lastpos + lenf)
err = binary.Write(pfbz2, signMagLittleEndian{}, int64(val))
if err != nil {
pfbz2.Close()
return err
}
lastscan = scan - lenb
lastpos = pos - lenb
lastoffset = pos - scan
}
}
err = pfbz2.Close()
if err != nil {
return err
}
// Compute size of compressed ctrl data
l64, err := patch.Seek(0, 1)
if err != nil {
return err
}
hdr.CtrlLen = int64(l64 - 32)
// Write compressed diff data
pfbz2, err = newBzip2Writer(patch)
if err != nil {
return err
}
n, err := pfbz2.Write(db[:dblen])
if err != nil {
pfbz2.Close()
return err
}
if n != dblen {
pfbz2.Close()
return io.ErrShortWrite
}
err = pfbz2.Close()
if err != nil {
return err
}
// Compute size of compressed diff data
n64, err := patch.Seek(0, 1)
if err != nil {
return err
}
hdr.DiffLen = n64 - l64
// Write compressed extra data
pfbz2, err = newBzip2Writer(patch)
if err != nil {
return err
}
n, err = pfbz2.Write(eb[:eblen])
if err != nil {
pfbz2.Close()
return err
}
if n != eblen {
pfbz2.Close()
return io.ErrShortWrite
}
err = pfbz2.Close()
if err != nil {
return err
}
// Seek to the beginning, write the header, and close the file
_, err = patch.Seek(0, 0)
if err != nil {
return err
}
err = binary.Write(patch, signMagLittleEndian{}, &hdr)
if err != nil {
return err
}
return nil
}