packfile: use a modified version of JGit DeltaIndex and DeltaIndexScanner
Signed-off-by: Miguel Molina <miguel@erizocosmi.co>
diff --git a/plumbing/format/packfile/delta_index.go b/plumbing/format/packfile/delta_index.go
new file mode 100644
index 0000000..fad9dc8
--- /dev/null
+++ b/plumbing/format/packfile/delta_index.go
@@ -0,0 +1,276 @@
+package packfile
+
+const blksz = 16
+const maxChainLength = 64
+
+// deltaIndex is a modified version of JGit's DeltaIndex adapted to our current
+// design.
+type deltaIndex struct {
+ table []int
+ entries []int
+ mask int
+}
+
+func (idx *deltaIndex) init(buf []byte) {
+ scanner := newDeltaIndexScanner(buf, len(buf))
+ idx.mask = scanner.mask
+ idx.table = scanner.table
+ idx.entries = make([]int, countEntries(scanner)+1)
+ idx.copyEntries(scanner)
+}
+
+func (idx *deltaIndex) findMatch(src, tgt []byte, tgtOffset int) (srcOffset, l int) {
+ if len(tgt) >= tgtOffset+s && len(src) >= blksz {
+ h := hashBlock(tgt, tgtOffset)
+ tIdx := h & idx.mask
+ eIdx := idx.table[tIdx]
+ if eIdx != 0 {
+ srcOffset = idx.entries[eIdx]
+ } else {
+ return
+ }
+
+ l = matchLength(src, tgt, tgtOffset, srcOffset)
+ }
+
+ return
+}
+
+func countEntries(scan *deltaIndexScanner) (cnt int) {
+ // Figure out exactly how many entries we need. As we do the
+ // enumeration truncate any delta chains longer than what we
+ // are willing to scan during encode. This keeps the encode
+ // logic linear in the size of the input rather than quadratic.
+ for i := 0; i < len(scan.table); i++ {
+ h := scan.table[i]
+ if h == 0 {
+ continue
+ }
+
+ size := 0
+ for {
+ size++
+ if size == maxChainLength {
+ scan.next[h] = 0
+ break
+ }
+ h = scan.next[h]
+
+ if h == 0 {
+ break
+ }
+ }
+ cnt += size
+ }
+
+ return
+}
+
+func (idx *deltaIndex) copyEntries(scanner *deltaIndexScanner) {
+ // Rebuild the entries list from the scanner, positioning all
+ // blocks in the same hash chain next to each other. We can
+ // then later discard the next list, along with the scanner.
+ //
+ next := 1
+ for i := 0; i < len(idx.table); i++ {
+ h := idx.table[i]
+ if h == 0 {
+ continue
+ }
+
+ idx.table[i] = next
+ for {
+ idx.entries[next] = scanner.entries[h]
+ next++
+ h = scanner.next[h]
+
+ if h == 0 {
+ break
+ }
+ }
+ }
+}
+
+type deltaIndexScanner struct {
+ table []int
+ entries []int
+ next []int
+ mask int
+ count int
+}
+
+func newDeltaIndexScanner(buf []byte, size int) *deltaIndexScanner {
+ size -= size % blksz
+ worstCaseBlockCnt := size / blksz
+ if worstCaseBlockCnt < 1 {
+ return new(deltaIndexScanner)
+ }
+
+ tableSize := tableSize(worstCaseBlockCnt)
+ scanner := &deltaIndexScanner{
+ table: make([]int, tableSize),
+ mask: tableSize - 1,
+ entries: make([]int, worstCaseBlockCnt+1),
+ next: make([]int, worstCaseBlockCnt+1),
+ }
+
+ scanner.scan(buf, size)
+ return scanner
+}
+
+// slightly modified version of JGit's DeltaIndexScanner. We store the offset on the entries
+// instead of the entries and the key, so we avoid operations to retrieve the offset later, as
+// we don't use the key.
+// See: https://github.com/eclipse/jgit/blob/005e5feb4ecd08c4e4d141a38b9e7942accb3212/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/DeltaIndexScanner.java
+func (s *deltaIndexScanner) scan(buf []byte, end int) {
+ lastHash := 0
+ ptr := end - blksz
+
+ for {
+ key := hashBlock(buf, ptr)
+ tIdx := key & s.mask
+ head := s.table[tIdx]
+ if head != 0 && lastHash == key {
+ s.entries[head] = ptr
+ } else {
+ s.count++
+ eIdx := s.count
+ s.entries[eIdx] = ptr
+ s.next[eIdx] = head
+ s.table[tIdx] = eIdx
+ }
+
+ lastHash = key
+ ptr -= blksz
+
+ if 0 > ptr {
+ break
+ }
+ }
+}
+
+func tableSize(worstCaseBlockCnt int) int {
+ shift := 32 - leadingZeros(uint32(worstCaseBlockCnt))
+ sz := 1 << uint(shift-1)
+ if sz < worstCaseBlockCnt {
+ sz <<= 1
+ }
+ return sz
+}
+
+// use https://golang.org/pkg/math/bits/#LeadingZeros32 in the future
+func leadingZeros(x uint32) (n int) {
+ if x >= 1<<16 {
+ x >>= 16
+ n = 16
+ }
+ if x >= 1<<8 {
+ x >>= 8
+ n += 8
+ }
+ n += int(len8tab[x])
+ return 32 - n
+}
+
+var len8tab = [256]uint8{
+ 0x00, 0x01, 0x02, 0x02, 0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04,
+ 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,
+ 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06,
+ 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06,
+ 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
+ 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
+ 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
+ 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+ 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
+}
+
+func hashBlock(raw []byte, ptr int) int {
+ var hash uint32
+
+ // The first 4 steps collapse out into a 4 byte big-endian decode,
+ // with a larger right shift as we combined shift lefts together.
+ //
+ hash = ((uint32(raw[ptr]) & 0xff) << 24) |
+ ((uint32(raw[ptr+1]) & 0xff) << 16) |
+ ((uint32(raw[ptr+2]) & 0xff) << 8) |
+ (uint32(raw[ptr+3]) & 0xff)
+ hash ^= T[hash>>31]
+
+ hash = ((hash << 8) | (uint32(raw[ptr+4]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+5]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+6]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+7]) & 0xff)) ^ T[hash>>23]
+
+ hash = ((hash << 8) | (uint32(raw[ptr+8]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+9]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+10]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+11]) & 0xff)) ^ T[hash>>23]
+
+ hash = ((hash << 8) | (uint32(raw[ptr+12]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+13]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+14]) & 0xff)) ^ T[hash>>23]
+ hash = ((hash << 8) | (uint32(raw[ptr+15]) & 0xff)) ^ T[hash>>23]
+
+ return int(hash)
+}
+
+var T = []uint32{0x00000000, 0xd4c6b32d, 0x7d4bd577,
+ 0xa98d665a, 0x2e5119c3, 0xfa97aaee, 0x531accb4, 0x87dc7f99,
+ 0x5ca23386, 0x886480ab, 0x21e9e6f1, 0xf52f55dc, 0x72f32a45,
+ 0xa6359968, 0x0fb8ff32, 0xdb7e4c1f, 0x6d82d421, 0xb944670c,
+ 0x10c90156, 0xc40fb27b, 0x43d3cde2, 0x97157ecf, 0x3e981895,
+ 0xea5eabb8, 0x3120e7a7, 0xe5e6548a, 0x4c6b32d0, 0x98ad81fd,
+ 0x1f71fe64, 0xcbb74d49, 0x623a2b13, 0xb6fc983e, 0x0fc31b6f,
+ 0xdb05a842, 0x7288ce18, 0xa64e7d35, 0x219202ac, 0xf554b181,
+ 0x5cd9d7db, 0x881f64f6, 0x536128e9, 0x87a79bc4, 0x2e2afd9e,
+ 0xfaec4eb3, 0x7d30312a, 0xa9f68207, 0x007be45d, 0xd4bd5770,
+ 0x6241cf4e, 0xb6877c63, 0x1f0a1a39, 0xcbcca914, 0x4c10d68d,
+ 0x98d665a0, 0x315b03fa, 0xe59db0d7, 0x3ee3fcc8, 0xea254fe5,
+ 0x43a829bf, 0x976e9a92, 0x10b2e50b, 0xc4745626, 0x6df9307c,
+ 0xb93f8351, 0x1f8636de, 0xcb4085f3, 0x62cde3a9, 0xb60b5084,
+ 0x31d72f1d, 0xe5119c30, 0x4c9cfa6a, 0x985a4947, 0x43240558,
+ 0x97e2b675, 0x3e6fd02f, 0xeaa96302, 0x6d751c9b, 0xb9b3afb6,
+ 0x103ec9ec, 0xc4f87ac1, 0x7204e2ff, 0xa6c251d2, 0x0f4f3788,
+ 0xdb8984a5, 0x5c55fb3c, 0x88934811, 0x211e2e4b, 0xf5d89d66,
+ 0x2ea6d179, 0xfa606254, 0x53ed040e, 0x872bb723, 0x00f7c8ba,
+ 0xd4317b97, 0x7dbc1dcd, 0xa97aaee0, 0x10452db1, 0xc4839e9c,
+ 0x6d0ef8c6, 0xb9c84beb, 0x3e143472, 0xead2875f, 0x435fe105,
+ 0x97995228, 0x4ce71e37, 0x9821ad1a, 0x31accb40, 0xe56a786d,
+ 0x62b607f4, 0xb670b4d9, 0x1ffdd283, 0xcb3b61ae, 0x7dc7f990,
+ 0xa9014abd, 0x008c2ce7, 0xd44a9fca, 0x5396e053, 0x8750537e,
+ 0x2edd3524, 0xfa1b8609, 0x2165ca16, 0xf5a3793b, 0x5c2e1f61,
+ 0x88e8ac4c, 0x0f34d3d5, 0xdbf260f8, 0x727f06a2, 0xa6b9b58f,
+ 0x3f0c6dbc, 0xebcade91, 0x4247b8cb, 0x96810be6, 0x115d747f,
+ 0xc59bc752, 0x6c16a108, 0xb8d01225, 0x63ae5e3a, 0xb768ed17,
+ 0x1ee58b4d, 0xca233860, 0x4dff47f9, 0x9939f4d4, 0x30b4928e,
+ 0xe47221a3, 0x528eb99d, 0x86480ab0, 0x2fc56cea, 0xfb03dfc7,
+ 0x7cdfa05e, 0xa8191373, 0x01947529, 0xd552c604, 0x0e2c8a1b,
+ 0xdaea3936, 0x73675f6c, 0xa7a1ec41, 0x207d93d8, 0xf4bb20f5,
+ 0x5d3646af, 0x89f0f582, 0x30cf76d3, 0xe409c5fe, 0x4d84a3a4,
+ 0x99421089, 0x1e9e6f10, 0xca58dc3d, 0x63d5ba67, 0xb713094a,
+ 0x6c6d4555, 0xb8abf678, 0x11269022, 0xc5e0230f, 0x423c5c96,
+ 0x96faefbb, 0x3f7789e1, 0xebb13acc, 0x5d4da2f2, 0x898b11df,
+ 0x20067785, 0xf4c0c4a8, 0x731cbb31, 0xa7da081c, 0x0e576e46,
+ 0xda91dd6b, 0x01ef9174, 0xd5292259, 0x7ca44403, 0xa862f72e,
+ 0x2fbe88b7, 0xfb783b9a, 0x52f55dc0, 0x8633eeed, 0x208a5b62,
+ 0xf44ce84f, 0x5dc18e15, 0x89073d38, 0x0edb42a1, 0xda1df18c,
+ 0x739097d6, 0xa75624fb, 0x7c2868e4, 0xa8eedbc9, 0x0163bd93,
+ 0xd5a50ebe, 0x52797127, 0x86bfc20a, 0x2f32a450, 0xfbf4177d,
+ 0x4d088f43, 0x99ce3c6e, 0x30435a34, 0xe485e919, 0x63599680,
+ 0xb79f25ad, 0x1e1243f7, 0xcad4f0da, 0x11aabcc5, 0xc56c0fe8,
+ 0x6ce169b2, 0xb827da9f, 0x3ffba506, 0xeb3d162b, 0x42b07071,
+ 0x9676c35c, 0x2f49400d, 0xfb8ff320, 0x5202957a, 0x86c42657,
+ 0x011859ce, 0xd5deeae3, 0x7c538cb9, 0xa8953f94, 0x73eb738b,
+ 0xa72dc0a6, 0x0ea0a6fc, 0xda6615d1, 0x5dba6a48, 0x897cd965,
+ 0x20f1bf3f, 0xf4370c12, 0x42cb942c, 0x960d2701, 0x3f80415b,
+ 0xeb46f276, 0x6c9a8def, 0xb85c3ec2, 0x11d15898, 0xc517ebb5,
+ 0x1e69a7aa, 0xcaaf1487, 0x632272dd, 0xb7e4c1f0, 0x3038be69,
+ 0xe4fe0d44, 0x4d736b1e, 0x99b5d833,
+}
diff --git a/plumbing/format/packfile/delta_selector.go b/plumbing/format/packfile/delta_selector.go
index 78b5733..021b520 100644
--- a/plumbing/format/packfile/delta_selector.go
+++ b/plumbing/format/packfile/delta_selector.go
@@ -172,7 +172,7 @@
}
func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
- indexMap := make(map[plumbing.Hash]deltaIndex)
+ indexMap := make(map[plumbing.Hash]*deltaIndex)
for i := 0; i < len(objectsToPack); i++ {
target := objectsToPack[i]
@@ -206,7 +206,7 @@
return nil
}
-func (dw *deltaSelector) tryToDeltify(indexMap map[plumbing.Hash]deltaIndex, base, target *ObjectToPack) error {
+func (dw *deltaSelector) tryToDeltify(indexMap map[plumbing.Hash]*deltaIndex, base, target *ObjectToPack) error {
// If the sizes are radically different, this is a bad pairing.
if target.Size() < base.Size()>>4 {
return nil
@@ -240,7 +240,7 @@
}
if _, ok := indexMap[base.Hash()]; !ok {
- indexMap[base.Hash()] = make(deltaIndex)
+ indexMap[base.Hash()] = new(deltaIndex)
}
// Now we can generate the delta using originals
diff --git a/plumbing/format/packfile/diff_delta.go b/plumbing/format/packfile/diff_delta.go
index 295b411..7c9360e 100644
--- a/plumbing/format/packfile/diff_delta.go
+++ b/plumbing/format/packfile/diff_delta.go
@@ -25,10 +25,10 @@
// To generate target again, you will need the obtained object and "base" one.
// Error will be returned if base or target object cannot be read.
func GetDelta(base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
- return getDelta(make(deltaIndex), base, target)
+ return getDelta(new(deltaIndex), base, target)
}
-func getDelta(index deltaIndex, base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
+func getDelta(index *deltaIndex, base, target plumbing.EncodedObject) (plumbing.EncodedObject, error) {
br, err := base.Reader()
if err != nil {
return nil, err
@@ -63,23 +63,23 @@
// DiffDelta returns the delta that transforms src into tgt.
func DiffDelta(src, tgt []byte) []byte {
- return diffDelta(make(deltaIndex), src, tgt)
+ return diffDelta(new(deltaIndex), src, tgt)
}
-func diffDelta(sindex deltaIndex, src []byte, tgt []byte) []byte {
+func diffDelta(index *deltaIndex, src []byte, tgt []byte) []byte {
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
buf.Write(deltaEncodeSize(len(src)))
buf.Write(deltaEncodeSize(len(tgt)))
- if len(sindex) == 0 {
- initMatch(sindex, src)
+ if len(index.entries) == 0 {
+ index.init(src)
}
ibuf := bufPool.Get().(*bytes.Buffer)
ibuf.Reset()
for i := 0; i < len(tgt); i++ {
- offset, l := findMatch(src, tgt, sindex, i)
+ offset, l := index.findMatch(src, tgt, i)
if l < s {
ibuf.WriteByte(tgt[i])
@@ -135,19 +135,6 @@
ibuf.Reset()
}
-func initMatch(index deltaIndex, src []byte) {
- i := 0
- for {
- if i+s > len(src) {
- break
- }
-
- ch := hashBuf(src[i : i+s])
- index[ch] = i
- i += s
- }
-}
-
// https://lemire.me/blog/2015/10/22/faster-hashing-without-effort/
func hashBuf(buf []byte) int64 {
var h int64
@@ -168,21 +155,6 @@
return h
}
-func findMatch(src, tgt []byte, sindex deltaIndex, tgtOffset int) (srcOffset, l int) {
- if len(tgt) >= tgtOffset+s {
- ch := hashBuf(tgt[tgtOffset : tgtOffset+s])
- var ok bool
- srcOffset, ok = sindex[ch]
- if !ok {
- return
- }
-
- l = matchLength(src, tgt, tgtOffset, srcOffset)
- }
-
- return
-}
-
func matchLength(src, tgt []byte, otgt, osrc int) int {
l := 0
for {
@@ -239,5 +211,3 @@
return append([]byte{byte(code)}, opcodes...)
}
-
-type deltaIndex map[int64]int
