diff options
Diffstat (limited to 'vendor/github.com/klauspost/compress/flate/level3.go')
| -rw-r--r-- | vendor/github.com/klauspost/compress/flate/level3.go | 225 |
1 files changed, 225 insertions, 0 deletions
diff --git a/vendor/github.com/klauspost/compress/flate/level3.go b/vendor/github.com/klauspost/compress/flate/level3.go new file mode 100644 index 000000000..4153d24c9 --- /dev/null +++ b/vendor/github.com/klauspost/compress/flate/level3.go @@ -0,0 +1,225 @@ +package flate + +// fastEncL3 +type fastEncL3 struct { + fastGen + table [tableSize]tableEntryPrev +} + +// Encode uses a similar algorithm to level 2, will check up to two candidates. +func (e *fastEncL3) Encode(dst *tokens, src []byte) { + const ( + inputMargin = 8 - 1 + minNonLiteralBlockSize = 1 + 1 + inputMargin + ) + + // Protect against e.cur wraparound. + for e.cur >= bufferReset { + if len(e.hist) == 0 { + for i := range e.table[:] { + e.table[i] = tableEntryPrev{} + } + e.cur = maxMatchOffset + break + } + // Shift down everything in the table that isn't already too far away. + minOff := e.cur + int32(len(e.hist)) - maxMatchOffset + for i := range e.table[:] { + v := e.table[i] + if v.Cur.offset <= minOff { + v.Cur.offset = 0 + } else { + v.Cur.offset = v.Cur.offset - e.cur + maxMatchOffset + } + if v.Prev.offset <= minOff { + v.Prev.offset = 0 + } else { + v.Prev.offset = v.Prev.offset - e.cur + maxMatchOffset + } + e.table[i] = v + } + e.cur = maxMatchOffset + } + + s := e.addBlock(src) + + // Skip if too small. + if len(src) < minNonLiteralBlockSize { + // We do not fill the token table. + // This will be picked up by caller. + dst.n = uint16(len(src)) + return + } + + // Override src + src = e.hist + nextEmit := s + + // 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. + cv := load3232(src, s) + for { + const skipLog = 6 + nextS := s + var candidate tableEntry + for { + nextHash := hash(cv) + s = nextS + nextS = s + 1 + (s-nextEmit)>>skipLog + if nextS > sLimit { + goto emitRemainder + } + candidates := e.table[nextHash] + now := load3232(src, nextS) + e.table[nextHash] = tableEntryPrev{Prev: candidates.Cur, Cur: tableEntry{offset: s + e.cur, val: cv}} + + // Check both candidates + candidate = candidates.Cur + offset := s - (candidate.offset - e.cur) + if cv == candidate.val { + if offset > maxMatchOffset { + cv = now + // Previous will also be invalid, we have nothing. + continue + } + o2 := s - (candidates.Prev.offset - e.cur) + if cv != candidates.Prev.val || o2 > maxMatchOffset { + break + } + // Both match and are valid, pick longest. + l1, l2 := matchLen(src[s+4:], src[s-offset+4:]), matchLen(src[s+4:], src[s-o2+4:]) + if l2 > l1 { + candidate = 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 + } + + // 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. + // + t := candidate.offset - e.cur + l := e.matchlenLong(s+4, t+4, src) + 4 + + // Extend backwards + for t > 0 && s > nextEmit && src[t-1] == src[s-1] { + s-- + t-- + l++ + } + if nextEmit < s { + emitLiteral(dst, src[nextEmit:s]) + } + + dst.AddMatchLong(l, uint32(s-t-baseMatchOffset)) + s += l + nextEmit = s + if nextS >= s { + s = nextS + 1 + } + + 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] = tableEntryPrev{ + Prev: e.table[nextHash].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. + x := load6432(src, s-3) + prevHash := hash(uint32(x)) + e.table[prevHash] = tableEntryPrev{ + Prev: e.table[prevHash].Cur, + Cur: tableEntry{offset: e.cur + s - 3, val: uint32(x)}, + } + x >>= 8 + prevHash = hash(uint32(x)) + + e.table[prevHash] = tableEntryPrev{ + Prev: e.table[prevHash].Cur, + Cur: tableEntry{offset: e.cur + s - 2, val: uint32(x)}, + } + x >>= 8 + prevHash = hash(uint32(x)) + + e.table[prevHash] = tableEntryPrev{ + Prev: e.table[prevHash].Cur, + Cur: tableEntry{offset: e.cur + s - 1, val: uint32(x)}, + } + x >>= 8 + currHash := hash(uint32(x)) + candidates := e.table[currHash] + cv = uint32(x) + e.table[currHash] = 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) + s++ + break + } + } + +emitRemainder: + if int(nextEmit) < len(src) { + // If nothing was added, don't encode literals. + if dst.n == 0 { + return + } + + emitLiteral(dst, src[nextEmit:]) + } +} |