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) } // findMatch returns the offset of src where the block starting at tgtOffset // is and the length of the match. A length of 0 means there was no match. A // length of -1 means the src length is lower than the blksz and whatever // other positive length is the length of the match in bytes. func (idx *deltaIndex) findMatch(src, tgt []byte, tgtOffset int) (srcOffset, l int) { if len(tgt) < tgtOffset+s { return 0, len(tgt) - tgtOffset } if len(src) < blksz { return 0, -1 } h := hashBlock(tgt, tgtOffset) tIdx := h & idx.mask eIdx := idx.table[tIdx] if eIdx == 0 { return } srcOffset = idx.entries[eIdx] l = matchLength(src, tgt, tgtOffset, srcOffset) return } func matchLength(src, tgt []byte, otgt, osrc int) (l int) { lensrc := len(src) lentgt := len(tgt) for (osrc < lensrc && otgt < lentgt) && src[osrc] == tgt[otgt] { l++ osrc++ otgt++ } 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 { // 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, }