diff options
Diffstat (limited to 'vendor/github.com/klauspost/compress/flate/snappy.go')
| -rw-r--r-- | vendor/github.com/klauspost/compress/flate/snappy.go | 900 |
1 files changed, 0 insertions, 900 deletions
diff --git a/vendor/github.com/klauspost/compress/flate/snappy.go b/vendor/github.com/klauspost/compress/flate/snappy.go deleted file mode 100644 index aebebd524..000000000 --- a/vendor/github.com/klauspost/compress/flate/snappy.go +++ /dev/null @@ -1,900 +0,0 @@ -// Copyright 2011 The Snappy-Go Authors. All rights reserved. -// Modified for deflate by Klaus Post (c) 2015. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE file. - -package flate - -// emitLiteral writes a literal chunk and returns the number of bytes written. -func emitLiteral(dst *tokens, lit []byte) { - ol := int(dst.n) - for i, v := range lit { - dst.tokens[(i+ol)&maxStoreBlockSize] = token(v) - } - dst.n += uint16(len(lit)) -} - -// emitCopy writes a copy chunk and returns the number of bytes written. -func emitCopy(dst *tokens, offset, length int) { - dst.tokens[dst.n] = matchToken(uint32(length-3), uint32(offset-minOffsetSize)) - dst.n++ -} - -type fastEnc interface { - Encode(dst *tokens, src []byte) - Reset() -} - -func newFastEnc(level int) fastEnc { - switch level { - case 1: - return &snappyL1{} - case 2: - return &snappyL2{snappyGen: snappyGen{cur: maxStoreBlockSize, prev: make([]byte, 0, maxStoreBlockSize)}} - case 3: - return &snappyL3{snappyGen: snappyGen{cur: maxStoreBlockSize, prev: make([]byte, 0, maxStoreBlockSize)}} - case 4: - return &snappyL4{snappyL3{snappyGen: snappyGen{cur: maxStoreBlockSize, prev: make([]byte, 0, maxStoreBlockSize)}}} - default: - panic("invalid level specified") - } -} - -const ( - tableBits = 14 // Bits used in the table - tableSize = 1 << tableBits // Size of the table - tableMask = tableSize - 1 // Mask for table indices. Redundant, but can eliminate bounds checks. - tableShift = 32 - tableBits // Right-shift to get the tableBits most significant bits of a uint32. - baseMatchOffset = 1 // The smallest match offset - baseMatchLength = 3 // The smallest match length per the RFC section 3.2.5 - maxMatchOffset = 1 << 15 // The largest match offset -) - -func load32(b []byte, i int) uint32 { - b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24 -} - -func load64(b []byte, i int) uint64 { - b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 | - uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56 -} - -func hash(u uint32) uint32 { - return (u * 0x1e35a7bd) >> tableShift -} - -// snappyL1 encapsulates level 1 compression -type snappyL1 struct{} - -func (e *snappyL1) Reset() {} - -func (e *snappyL1) Encode(dst *tokens, src []byte) { - const ( - inputMargin = 16 - 1 - minNonLiteralBlockSize = 1 + 1 + inputMargin - ) - - // This check isn't in the Snappy implementation, but there, the caller - // instead of the callee handles this case. - if len(src) < minNonLiteralBlockSize { - // We do not fill the token table. - // This will be picked up by caller. - dst.n = uint16(len(src)) - return - } - - // Initialize the hash table. - // - // The table element type is uint16, as s < sLimit and sLimit < len(src) - // and len(src) <= maxStoreBlockSize and maxStoreBlockSize == 65535. - var table [tableSize]uint16 - - // sLimit is when to stop looking for offset/length copies. The inputMargin - // lets us use a fast path for emitLiteral in the main loop, while we are - // looking for copies. - sLimit := len(src) - inputMargin - - // nextEmit is where in src the next emitLiteral should start from. - nextEmit := 0 - - // The encoded form must start with a literal, as there are no previous - // bytes to copy, so we start looking for hash matches at s == 1. - s := 1 - nextHash := hash(load32(src, s)) - - for { - // Copied from the C++ snappy implementation: - // - // Heuristic match skipping: If 32 bytes are scanned with no matches - // found, start looking only at every other byte. If 32 more bytes are - // scanned (or skipped), look at every third byte, etc.. When a match - // is found, immediately go back to looking at every byte. This is a - // small loss (~5% performance, ~0.1% density) for compressible data - // due to more bookkeeping, but for non-compressible data (such as - // JPEG) it's a huge win since the compressor quickly "realizes" the - // data is incompressible and doesn't bother looking for matches - // everywhere. - // - // The "skip" variable keeps track of how many bytes there are since - // the last match; dividing it by 32 (ie. right-shifting by five) gives - // the number of bytes to move ahead for each iteration. - skip := 32 - - nextS := s - candidate := 0 - for { - s = nextS - bytesBetweenHashLookups := skip >> 5 - nextS = s + bytesBetweenHashLookups - skip += bytesBetweenHashLookups - if nextS > sLimit { - goto emitRemainder - } - candidate = int(table[nextHash&tableMask]) - table[nextHash&tableMask] = uint16(s) - nextHash = hash(load32(src, nextS)) - if s-candidate <= maxMatchOffset && load32(src, s) == load32(src, candidate) { - break - } - } - - // A 4-byte match has been found. We'll later see if more than 4 bytes - // match. But, prior to the match, src[nextEmit:s] are unmatched. Emit - // them as literal bytes. - emitLiteral(dst, src[nextEmit:s]) - - // Call emitCopy, and then see if another emitCopy could be our next - // move. Repeat until we find no match for the input immediately after - // what was consumed by the last emitCopy call. - // - // If we exit this loop normally then we need to call emitLiteral next, - // though we don't yet know how big the literal will be. We handle that - // by proceeding to the next iteration of the main loop. We also can - // exit this loop via goto if we get close to exhausting the input. - for { - // Invariant: we have a 4-byte match at s, and no need to emit any - // literal bytes prior to s. - base := s - - // Extend the 4-byte match as long as possible. - // - // This is an inlined version of Snappy's: - // s = extendMatch(src, candidate+4, s+4) - s += 4 - s1 := base + maxMatchLength - if s1 > len(src) { - s1 = len(src) - } - a := src[s:s1] - b := src[candidate+4:] - b = b[:len(a)] - l := len(a) - for i := range a { - if a[i] != b[i] { - l = i - break - } - } - s += l - - // matchToken is flate's equivalent of Snappy's emitCopy. - dst.tokens[dst.n] = matchToken(uint32(s-base-baseMatchLength), uint32(base-candidate-baseMatchOffset)) - dst.n++ - nextEmit = s - if s >= sLimit { - goto emitRemainder - } - - // We could immediately start working at s now, but to improve - // compression we first update the hash table at s-1 and at s. If - // another emitCopy is not our next move, also calculate nextHash - // at s+1. At least on GOARCH=amd64, these three hash calculations - // are faster as one load64 call (with some shifts) instead of - // three load32 calls. - x := load64(src, s-1) - prevHash := hash(uint32(x >> 0)) - table[prevHash&tableMask] = uint16(s - 1) - currHash := hash(uint32(x >> 8)) - candidate = int(table[currHash&tableMask]) - table[currHash&tableMask] = uint16(s) - if s-candidate > maxMatchOffset || uint32(x>>8) != load32(src, candidate) { - nextHash = hash(uint32(x >> 16)) - s++ - break - } - } - } - -emitRemainder: - if nextEmit < len(src) { - emitLiteral(dst, src[nextEmit:]) - } -} - -type tableEntry struct { - val uint32 - offset int32 -} - -func load3232(b []byte, i int32) uint32 { - b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24 -} - -func load6432(b []byte, i int32) uint64 { - b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 | - uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56 -} - -// snappyGen maintains the table for matches, -// and the previous byte block for level 2. -// This is the generic implementation. -type snappyGen struct { - prev []byte - cur int32 -} - -// snappyGen maintains the table for matches, -// and the previous byte block for level 2. -// This is the generic implementation. -type snappyL2 struct { - snappyGen - table [tableSize]tableEntry -} - -// EncodeL2 uses a similar algorithm to level 1, but is capable -// of matching across blocks giving better compression at a small slowdown. -func (e *snappyL2) Encode(dst *tokens, src []byte) { - const ( - inputMargin = 8 - 1 - minNonLiteralBlockSize = 1 + 1 + inputMargin - ) - - // Protect against e.cur wraparound. - if e.cur > 1<<30 { - for i := range e.table[:] { - e.table[i] = tableEntry{} - } - e.cur = maxStoreBlockSize - } - - // This check isn't in the Snappy implementation, but there, the caller - // instead of the callee handles this case. - if len(src) < minNonLiteralBlockSize { - // We do not fill the token table. - // This will be picked up by caller. - dst.n = uint16(len(src)) - e.cur += maxStoreBlockSize - e.prev = e.prev[:0] - return - } - - // sLimit is when to stop looking for offset/length copies. The inputMargin - // lets us use a fast path for emitLiteral in the main loop, while we are - // looking for copies. - sLimit := int32(len(src) - inputMargin) - - // nextEmit is where in src the next emitLiteral should start from. - nextEmit := int32(0) - s := int32(0) - cv := load3232(src, s) - nextHash := hash(cv) - - for { - // Copied from the C++ snappy implementation: - // - // Heuristic match skipping: If 32 bytes are scanned with no matches - // found, start looking only at every other byte. If 32 more bytes are - // scanned (or skipped), look at every third byte, etc.. When a match - // is found, immediately go back to looking at every byte. This is a - // small loss (~5% performance, ~0.1% density) for compressible data - // due to more bookkeeping, but for non-compressible data (such as - // JPEG) it's a huge win since the compressor quickly "realizes" the - // data is incompressible and doesn't bother looking for matches - // everywhere. - // - // The "skip" variable keeps track of how many bytes there are since - // the last match; dividing it by 32 (ie. right-shifting by five) gives - // the number of bytes to move ahead for each iteration. - skip := int32(32) - - nextS := s - var candidate tableEntry - for { - s = nextS - bytesBetweenHashLookups := skip >> 5 - nextS = s + bytesBetweenHashLookups - skip += bytesBetweenHashLookups - if nextS > sLimit { - goto emitRemainder - } - candidate = e.table[nextHash&tableMask] - now := load3232(src, nextS) - e.table[nextHash&tableMask] = tableEntry{offset: s + e.cur, val: cv} - nextHash = hash(now) - - offset := s - (candidate.offset - e.cur) - if offset > maxMatchOffset || cv != candidate.val { - // Out of range or not matched. - cv = now - continue - } - break - } - - // A 4-byte match has been found. We'll later see if more than 4 bytes - // match. But, prior to the match, src[nextEmit:s] are unmatched. Emit - // them as literal bytes. - emitLiteral(dst, src[nextEmit:s]) - - // Call emitCopy, and then see if another emitCopy could be our next - // move. Repeat until we find no match for the input immediately after - // what was consumed by the last emitCopy call. - // - // If we exit this loop normally then we need to call emitLiteral next, - // though we don't yet know how big the literal will be. We handle that - // by proceeding to the next iteration of the main loop. We also can - // exit this loop via goto if we get close to exhausting the input. - for { - // Invariant: we have a 4-byte match at s, and no need to emit any - // literal bytes prior to s. - - // Extend the 4-byte match as long as possible. - // - s += 4 - t := candidate.offset - e.cur + 4 - l := e.matchlen(s, t, src) - - // matchToken is flate's equivalent of Snappy's emitCopy. (length,offset) - dst.tokens[dst.n] = matchToken(uint32(l+4-baseMatchLength), uint32(s-t-baseMatchOffset)) - dst.n++ - s += l - nextEmit = s - if s >= sLimit { - t += l - // Index first pair after match end. - if int(t+4) < len(src) && t > 0 { - cv := load3232(src, t) - e.table[hash(cv)&tableMask] = tableEntry{offset: t + e.cur, val: cv} - } - goto emitRemainder - } - - // We could immediately start working at s now, but to improve - // compression we first update the hash table at s-1 and at s. If - // another emitCopy is not our next move, also calculate nextHash - // at s+1. At least on GOARCH=amd64, these three hash calculations - // are faster as one load64 call (with some shifts) instead of - // three load32 calls. - x := load6432(src, s-1) - prevHash := hash(uint32(x)) - e.table[prevHash&tableMask] = tableEntry{offset: e.cur + s - 1, val: uint32(x)} - x >>= 8 - currHash := hash(uint32(x)) - candidate = e.table[currHash&tableMask] - e.table[currHash&tableMask] = tableEntry{offset: e.cur + s, val: uint32(x)} - - offset := s - (candidate.offset - e.cur) - if offset > maxMatchOffset || uint32(x) != candidate.val { - cv = uint32(x >> 8) - nextHash = hash(cv) - s++ - break - } - } - } - -emitRemainder: - if int(nextEmit) < len(src) { - emitLiteral(dst, src[nextEmit:]) - } - e.cur += int32(len(src)) - e.prev = e.prev[:len(src)] - copy(e.prev, src) -} - -type tableEntryPrev struct { - Cur tableEntry - Prev tableEntry -} - -// snappyL3 -type snappyL3 struct { - snappyGen - table [tableSize]tableEntryPrev -} - -// Encode uses a similar algorithm to level 2, will check up to two candidates. -func (e *snappyL3) Encode(dst *tokens, src []byte) { - const ( - inputMargin = 8 - 1 - minNonLiteralBlockSize = 1 + 1 + inputMargin - ) - - // Protect against e.cur wraparound. - if e.cur > 1<<30 { - for i := range e.table[:] { - e.table[i] = tableEntryPrev{} - } - e.snappyGen = snappyGen{cur: maxStoreBlockSize, prev: e.prev[:0]} - } - - // This check isn't in the Snappy implementation, but there, the caller - // instead of the callee handles this case. - if len(src) < minNonLiteralBlockSize { - // We do not fill the token table. - // This will be picked up by caller. - dst.n = uint16(len(src)) - e.cur += maxStoreBlockSize - e.prev = e.prev[:0] - return - } - - // sLimit is when to stop looking for offset/length copies. The inputMargin - // lets us use a fast path for emitLiteral in the main loop, while we are - // looking for copies. - sLimit := int32(len(src) - inputMargin) - - // nextEmit is where in src the next emitLiteral should start from. - nextEmit := int32(0) - s := int32(0) - cv := load3232(src, s) - nextHash := hash(cv) - - for { - // Copied from the C++ snappy implementation: - // - // Heuristic match skipping: If 32 bytes are scanned with no matches - // found, start looking only at every other byte. If 32 more bytes are - // scanned (or skipped), look at every third byte, etc.. When a match - // is found, immediately go back to looking at every byte. This is a - // small loss (~5% performance, ~0.1% density) for compressible data - // due to more bookkeeping, but for non-compressible data (such as - // JPEG) it's a huge win since the compressor quickly "realizes" the - // data is incompressible and doesn't bother looking for matches - // everywhere. - // - // The "skip" variable keeps track of how many bytes there are since - // the last match; dividing it by 32 (ie. right-shifting by five) gives - // the number of bytes to move ahead for each iteration. - skip := int32(32) - - nextS := s - var candidate tableEntry - for { - s = nextS - bytesBetweenHashLookups := skip >> 5 - nextS = s + bytesBetweenHashLookups - skip += bytesBetweenHashLookups - if nextS > sLimit { - goto emitRemainder - } - candidates := e.table[nextHash&tableMask] - now := load3232(src, nextS) - e.table[nextHash&tableMask] = tableEntryPrev{Prev: candidates.Cur, Cur: tableEntry{offset: s + e.cur, val: cv}} - nextHash = hash(now) - - // Check both candidates - candidate = candidates.Cur - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - break - } - } else { - // We only check if value mismatches. - // Offset will always be invalid in other cases. - candidate = candidates.Prev - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - break - } - } - } - cv = now - } - - // A 4-byte match has been found. We'll later see if more than 4 bytes - // match. But, prior to the match, src[nextEmit:s] are unmatched. Emit - // them as literal bytes. - emitLiteral(dst, src[nextEmit:s]) - - // Call emitCopy, and then see if another emitCopy could be our next - // move. Repeat until we find no match for the input immediately after - // what was consumed by the last emitCopy call. - // - // If we exit this loop normally then we need to call emitLiteral next, - // though we don't yet know how big the literal will be. We handle that - // by proceeding to the next iteration of the main loop. We also can - // exit this loop via goto if we get close to exhausting the input. - for { - // Invariant: we have a 4-byte match at s, and no need to emit any - // literal bytes prior to s. - - // Extend the 4-byte match as long as possible. - // - s += 4 - t := candidate.offset - e.cur + 4 - l := e.matchlen(s, t, src) - - // matchToken is flate's equivalent of Snappy's emitCopy. (length,offset) - dst.tokens[dst.n] = matchToken(uint32(l+4-baseMatchLength), uint32(s-t-baseMatchOffset)) - dst.n++ - s += l - nextEmit = s - if s >= sLimit { - t += l - // Index first pair after match end. - if int(t+4) < len(src) && t > 0 { - cv := load3232(src, t) - nextHash = hash(cv) - e.table[nextHash&tableMask] = tableEntryPrev{ - Prev: e.table[nextHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + t, val: cv}, - } - } - goto emitRemainder - } - - // We could immediately start working at s now, but to improve - // compression we first update the hash table at s-3 to s. If - // another emitCopy is not our next move, also calculate nextHash - // at s+1. At least on GOARCH=amd64, these three hash calculations - // are faster as one load64 call (with some shifts) instead of - // three load32 calls. - x := load6432(src, s-3) - prevHash := hash(uint32(x)) - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 3, val: uint32(x)}, - } - x >>= 8 - prevHash = hash(uint32(x)) - - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 2, val: uint32(x)}, - } - x >>= 8 - prevHash = hash(uint32(x)) - - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 1, val: uint32(x)}, - } - x >>= 8 - currHash := hash(uint32(x)) - candidates := e.table[currHash&tableMask] - cv = uint32(x) - e.table[currHash&tableMask] = tableEntryPrev{ - Prev: candidates.Cur, - Cur: tableEntry{offset: s + e.cur, val: cv}, - } - - // Check both candidates - candidate = candidates.Cur - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - continue - } - } else { - // We only check if value mismatches. - // Offset will always be invalid in other cases. - candidate = candidates.Prev - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - continue - } - } - } - cv = uint32(x >> 8) - nextHash = hash(cv) - s++ - break - } - } - -emitRemainder: - if int(nextEmit) < len(src) { - emitLiteral(dst, src[nextEmit:]) - } - e.cur += int32(len(src)) - e.prev = e.prev[:len(src)] - copy(e.prev, src) -} - -// snappyL4 -type snappyL4 struct { - snappyL3 -} - -// Encode uses a similar algorithm to level 3, -// but will check up to two candidates if first isn't long enough. -func (e *snappyL4) Encode(dst *tokens, src []byte) { - const ( - inputMargin = 8 - 3 - minNonLiteralBlockSize = 1 + 1 + inputMargin - matchLenGood = 12 - ) - - // Protect against e.cur wraparound. - if e.cur > 1<<30 { - for i := range e.table[:] { - e.table[i] = tableEntryPrev{} - } - e.snappyGen = snappyGen{cur: maxStoreBlockSize, prev: e.prev[:0]} - } - - // This check isn't in the Snappy implementation, but there, the caller - // instead of the callee handles this case. - if len(src) < minNonLiteralBlockSize { - // We do not fill the token table. - // This will be picked up by caller. - dst.n = uint16(len(src)) - e.cur += maxStoreBlockSize - e.prev = e.prev[:0] - return - } - - // sLimit is when to stop looking for offset/length copies. The inputMargin - // lets us use a fast path for emitLiteral in the main loop, while we are - // looking for copies. - sLimit := int32(len(src) - inputMargin) - - // nextEmit is where in src the next emitLiteral should start from. - nextEmit := int32(0) - s := int32(0) - cv := load3232(src, s) - nextHash := hash(cv) - - for { - // Copied from the C++ snappy implementation: - // - // Heuristic match skipping: If 32 bytes are scanned with no matches - // found, start looking only at every other byte. If 32 more bytes are - // scanned (or skipped), look at every third byte, etc.. When a match - // is found, immediately go back to looking at every byte. This is a - // small loss (~5% performance, ~0.1% density) for compressible data - // due to more bookkeeping, but for non-compressible data (such as - // JPEG) it's a huge win since the compressor quickly "realizes" the - // data is incompressible and doesn't bother looking for matches - // everywhere. - // - // The "skip" variable keeps track of how many bytes there are since - // the last match; dividing it by 32 (ie. right-shifting by five) gives - // the number of bytes to move ahead for each iteration. - skip := int32(32) - - nextS := s - var candidate tableEntry - var candidateAlt tableEntry - for { - s = nextS - bytesBetweenHashLookups := skip >> 5 - nextS = s + bytesBetweenHashLookups - skip += bytesBetweenHashLookups - if nextS > sLimit { - goto emitRemainder - } - candidates := e.table[nextHash&tableMask] - now := load3232(src, nextS) - e.table[nextHash&tableMask] = tableEntryPrev{Prev: candidates.Cur, Cur: tableEntry{offset: s + e.cur, val: cv}} - nextHash = hash(now) - - // Check both candidates - candidate = candidates.Cur - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset < maxMatchOffset { - offset = s - (candidates.Prev.offset - e.cur) - if cv == candidates.Prev.val && offset < maxMatchOffset { - candidateAlt = candidates.Prev - } - break - } - } else { - // We only check if value mismatches. - // Offset will always be invalid in other cases. - candidate = candidates.Prev - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset < maxMatchOffset { - break - } - } - } - cv = now - } - - // A 4-byte match has been found. We'll later see if more than 4 bytes - // match. But, prior to the match, src[nextEmit:s] are unmatched. Emit - // them as literal bytes. - emitLiteral(dst, src[nextEmit:s]) - - // Call emitCopy, and then see if another emitCopy could be our next - // move. Repeat until we find no match for the input immediately after - // what was consumed by the last emitCopy call. - // - // If we exit this loop normally then we need to call emitLiteral next, - // though we don't yet know how big the literal will be. We handle that - // by proceeding to the next iteration of the main loop. We also can - // exit this loop via goto if we get close to exhausting the input. - for { - // Invariant: we have a 4-byte match at s, and no need to emit any - // literal bytes prior to s. - - // Extend the 4-byte match as long as possible. - // - s += 4 - t := candidate.offset - e.cur + 4 - l := e.matchlen(s, t, src) - // Try alternative candidate if match length < matchLenGood. - if l < matchLenGood-4 && candidateAlt.offset != 0 { - t2 := candidateAlt.offset - e.cur + 4 - l2 := e.matchlen(s, t2, src) - if l2 > l { - l = l2 - t = t2 - } - } - // matchToken is flate's equivalent of Snappy's emitCopy. (length,offset) - dst.tokens[dst.n] = matchToken(uint32(l+4-baseMatchLength), uint32(s-t-baseMatchOffset)) - dst.n++ - s += l - nextEmit = s - if s >= sLimit { - t += l - // Index first pair after match end. - if int(t+4) < len(src) && t > 0 { - cv := load3232(src, t) - nextHash = hash(cv) - e.table[nextHash&tableMask] = tableEntryPrev{ - Prev: e.table[nextHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + t, val: cv}, - } - } - goto emitRemainder - } - - // We could immediately start working at s now, but to improve - // compression we first update the hash table at s-3 to s. If - // another emitCopy is not our next move, also calculate nextHash - // at s+1. At least on GOARCH=amd64, these three hash calculations - // are faster as one load64 call (with some shifts) instead of - // three load32 calls. - x := load6432(src, s-3) - prevHash := hash(uint32(x)) - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 3, val: uint32(x)}, - } - x >>= 8 - prevHash = hash(uint32(x)) - - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 2, val: uint32(x)}, - } - x >>= 8 - prevHash = hash(uint32(x)) - - e.table[prevHash&tableMask] = tableEntryPrev{ - Prev: e.table[prevHash&tableMask].Cur, - Cur: tableEntry{offset: e.cur + s - 1, val: uint32(x)}, - } - x >>= 8 - currHash := hash(uint32(x)) - candidates := e.table[currHash&tableMask] - cv = uint32(x) - e.table[currHash&tableMask] = tableEntryPrev{ - Prev: candidates.Cur, - Cur: tableEntry{offset: s + e.cur, val: cv}, - } - - // Check both candidates - candidate = candidates.Cur - candidateAlt = tableEntry{} - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - offset = s - (candidates.Prev.offset - e.cur) - if cv == candidates.Prev.val && offset <= maxMatchOffset { - candidateAlt = candidates.Prev - } - continue - } - } else { - // We only check if value mismatches. - // Offset will always be invalid in other cases. - candidate = candidates.Prev - if cv == candidate.val { - offset := s - (candidate.offset - e.cur) - if offset <= maxMatchOffset { - continue - } - } - } - cv = uint32(x >> 8) - nextHash = hash(cv) - s++ - break - } - } - -emitRemainder: - if int(nextEmit) < len(src) { - emitLiteral(dst, src[nextEmit:]) - } - e.cur += int32(len(src)) - e.prev = e.prev[:len(src)] - copy(e.prev, src) -} - -func (e *snappyGen) matchlen(s, t int32, src []byte) int32 { - s1 := int(s) + maxMatchLength - 4 - if s1 > len(src) { - s1 = len(src) - } - - // If we are inside the current block - if t >= 0 { - b := src[t:] - a := src[s:s1] - b = b[:len(a)] - // Extend the match to be as long as possible. - for i := range a { - if a[i] != b[i] { - return int32(i) - } - } - return int32(len(a)) - } - - // We found a match in the previous block. - tp := int32(len(e.prev)) + t - if tp < 0 { - return 0 - } - - // Extend the match to be as long as possible. - a := src[s:s1] - b := e.prev[tp:] - if len(b) > len(a) { - b = b[:len(a)] - } - a = a[:len(b)] - for i := range b { - if a[i] != b[i] { - return int32(i) - } - } - - // If we reached our limit, we matched everything we are - // allowed to in the previous block and we return. - n := int32(len(b)) - if int(s+n) == s1 { - return n - } - - // Continue looking for more matches in the current block. - a = src[s+n : s1] - b = src[:len(a)] - for i := range a { - if a[i] != b[i] { - return int32(i) + n - } - } - return int32(len(a)) + n -} - -// Reset the encoding table. -func (e *snappyGen) Reset() { - e.prev = e.prev[:0] - e.cur += maxMatchOffset -} |