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// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.
package zstd
import (
"github.com/klauspost/compress/huff0"
)
// history contains the information transferred between blocks.
type history struct {
// Literal decompression
huffTree *huff0.Scratch
// Sequence decompression
decoders sequenceDecs
recentOffsets [3]int
// History buffer...
b []byte
// ignoreBuffer is meant to ignore a number of bytes
// when checking for matches in history
ignoreBuffer int
windowSize int
allocFrameBuffer int // needed?
error bool
dict *dict
}
// reset will reset the history to initial state of a frame.
// The history must already have been initialized to the desired size.
func (h *history) reset() {
h.b = h.b[:0]
h.ignoreBuffer = 0
h.error = false
h.recentOffsets = [3]int{1, 4, 8}
h.decoders.freeDecoders()
h.decoders = sequenceDecs{br: h.decoders.br}
h.freeHuffDecoder()
h.huffTree = nil
h.dict = nil
//printf("history created: %+v (l: %d, c: %d)", *h, len(h.b), cap(h.b))
}
func (h *history) freeHuffDecoder() {
if h.huffTree != nil {
if h.dict == nil || h.dict.litEnc != h.huffTree {
huffDecoderPool.Put(h.huffTree)
h.huffTree = nil
}
}
}
func (h *history) setDict(dict *dict) {
if dict == nil {
return
}
h.dict = dict
h.decoders.litLengths = dict.llDec
h.decoders.offsets = dict.ofDec
h.decoders.matchLengths = dict.mlDec
h.decoders.dict = dict.content
h.recentOffsets = dict.offsets
h.huffTree = dict.litEnc
}
// append bytes to history.
// This function will make sure there is space for it,
// if the buffer has been allocated with enough extra space.
func (h *history) append(b []byte) {
if len(b) >= h.windowSize {
// Discard all history by simply overwriting
h.b = h.b[:h.windowSize]
copy(h.b, b[len(b)-h.windowSize:])
return
}
// If there is space, append it.
if len(b) < cap(h.b)-len(h.b) {
h.b = append(h.b, b...)
return
}
// Move data down so we only have window size left.
// We know we have less than window size in b at this point.
discard := len(b) + len(h.b) - h.windowSize
copy(h.b, h.b[discard:])
h.b = h.b[:h.windowSize]
copy(h.b[h.windowSize-len(b):], b)
}
// ensureBlock will ensure there is space for at least one block...
func (h *history) ensureBlock() {
if cap(h.b) < h.allocFrameBuffer {
h.b = make([]byte, 0, h.allocFrameBuffer)
return
}
avail := cap(h.b) - len(h.b)
if avail >= h.windowSize || avail > maxCompressedBlockSize {
return
}
// Move data down so we only have window size left.
// We know we have less than window size in b at this point.
discard := len(h.b) - h.windowSize
copy(h.b, h.b[discard:])
h.b = h.b[:h.windowSize]
}
// append bytes to history without ever discarding anything.
func (h *history) appendKeep(b []byte) {
h.b = append(h.b, b...)
}
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