From 508a89726c9287b3fb5daac23b7957d4297bc42a Mon Sep 17 00:00:00 2001 From: Miguel Molina Date: Wed, 6 Sep 2017 18:14:55 +0200 Subject: packfile: use a modified version of JGit DeltaIndex and DeltaIndexScanner Signed-off-by: Miguel Molina --- plumbing/format/packfile/delta_index.go | 276 +++++++++++++++++++++++++++++ plumbing/format/packfile/delta_selector.go | 6 +- plumbing/format/packfile/diff_delta.go | 44 +---- 3 files changed, 286 insertions(+), 40 deletions(-) create mode 100644 plumbing/format/packfile/delta_index.go (limited to 'plumbing') 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) sort(objectsToPack []*ObjectToPack) { } 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 @@ func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error { 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 @@ func (dw *deltaSelector) tryToDeltify(indexMap map[plumbing.Hash]deltaIndex, bas } 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 @@ const ( // 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 @@ func getDelta(index deltaIndex, base, target plumbing.EncodedObject) (plumbing.E // 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 @@ func encodeInsertOperation(ibuf, buf *bytes.Buffer) { 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 @@ func hashBuf(buf []byte) int64 { 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 @@ func encodeCopyOperation(offset, length int) []byte { return append([]byte{byte(code)}, opcodes...) } - -type deltaIndex map[int64]int -- cgit