95 lines
2.5 KiB
Go
95 lines
2.5 KiB
Go
// Copyright 2014 The zappy Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Copyright 2011 The Snappy-Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the SNAPPY-GO-LICENSE file.
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// +build !cgo purego
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package zappy
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import (
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"encoding/binary"
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"fmt"
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"math"
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"github.com/cznic/internal/buffer"
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)
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func puregoEncode() bool { return true }
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// Encode returns the encoded form of src. The returned slice may be a sub-
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// slice of buf if buf was large enough to hold the entire encoded block.
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// Otherwise, a newly allocated slice will be returned.
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// It is valid to pass a nil buf.
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func Encode(buf, src []byte) ([]byte, error) {
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if n := MaxEncodedLen(len(src)); len(buf) < n {
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buf = *buffer.Get(n)
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}
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if len(src) > math.MaxInt32 {
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return nil, fmt.Errorf("zappy.Encode: too long data: %d bytes", len(src))
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}
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// The block starts with the varint-encoded length of the decompressed bytes.
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d := binary.PutUvarint(buf, uint64(len(src)))
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// Return early if src is short.
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if len(src) <= 4 {
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if len(src) != 0 {
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d += emitLiteral(buf[d:], src)
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}
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return buf[:d], nil
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}
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// Iterate over the source bytes.
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var (
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table [1 << 12]int // Hash table
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s int // The iterator position.
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t int // The last position with the same hash as s.
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lit int // The start position of any pending literal bytes.
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)
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for lim := len(src) - 3; s < lim; {
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// Update the hash table.
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b0, b1, b2, b3 := src[s], src[s+1], src[s+2], src[s+3]
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h := uint32(b0) | uint32(b1)<<8 | uint32(b2)<<16 | uint32(b3)<<24
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more:
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p := &table[(h*0x1e35a7bd)>>20]
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t, *p = *p, s
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// If t is invalid or src[s:s+4] differs from src[t:t+4], accumulate a literal byte.
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if t == 0 || s-t >= maxOffset || b0 != src[t] || b1 != src[t+1] || b2 != src[t+2] || b3 != src[t+3] {
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s++
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if s >= lim {
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break
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}
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b0, b1, b2, b3 = b1, b2, b3, src[s+3]
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h = h>>8 | uint32(b3)<<24
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goto more
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}
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// Otherwise, we have a match. First, emit any pending literal bytes.
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if lit != s {
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d += emitLiteral(buf[d:], src[lit:s])
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}
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// Extend the match to be as long as possible.
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s0 := s
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s, t = s+4, t+4
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for s < len(src) && src[s] == src[t] {
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s++
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t++
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}
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// Emit the copied bytes.
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d += emitCopy(buf[d:], s-t, s-s0)
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lit = s
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}
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// Emit any final pending literal bytes and return.
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if lit != len(src) {
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d += emitLiteral(buf[d:], src[lit:])
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}
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return buf[:d], nil
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}
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