1// Copyright 2019+ Klaus Post. All rights reserved.
2// License information can be found in the LICENSE file.
3// Based on work by Yann Collet, released under BSD License.
4
5package zstd
6
7import (
8	"github.com/klauspost/compress/huff0"
9)
10
11// history contains the information transferred between blocks.
12type history struct {
13	b             []byte
14	huffTree      *huff0.Scratch
15	recentOffsets [3]int
16	decoders      sequenceDecs
17	windowSize    int
18	maxSize       int
19	error         bool
20	dict          *dict
21}
22
23// reset will reset the history to initial state of a frame.
24// The history must already have been initialized to the desired size.
25func (h *history) reset() {
26	h.b = h.b[:0]
27	h.error = false
28	h.recentOffsets = [3]int{1, 4, 8}
29	if f := h.decoders.litLengths.fse; f != nil && !f.preDefined {
30		fseDecoderPool.Put(f)
31	}
32	if f := h.decoders.offsets.fse; f != nil && !f.preDefined {
33		fseDecoderPool.Put(f)
34	}
35	if f := h.decoders.matchLengths.fse; f != nil && !f.preDefined {
36		fseDecoderPool.Put(f)
37	}
38	h.decoders = sequenceDecs{}
39	if h.huffTree != nil {
40		if h.dict == nil || h.dict.litEnc != h.huffTree {
41			huffDecoderPool.Put(h.huffTree)
42		}
43	}
44	h.huffTree = nil
45	h.dict = nil
46	//printf("history created: %+v (l: %d, c: %d)", *h, len(h.b), cap(h.b))
47}
48
49func (h *history) setDict(dict *dict) {
50	if dict == nil {
51		return
52	}
53	h.dict = dict
54	h.decoders.litLengths = dict.llDec
55	h.decoders.offsets = dict.ofDec
56	h.decoders.matchLengths = dict.mlDec
57	h.recentOffsets = dict.offsets
58	h.huffTree = dict.litEnc
59}
60
61// append bytes to history.
62// This function will make sure there is space for it,
63// if the buffer has been allocated with enough extra space.
64func (h *history) append(b []byte) {
65	if len(b) >= h.windowSize {
66		// Discard all history by simply overwriting
67		h.b = h.b[:h.windowSize]
68		copy(h.b, b[len(b)-h.windowSize:])
69		return
70	}
71
72	// If there is space, append it.
73	if len(b) < cap(h.b)-len(h.b) {
74		h.b = append(h.b, b...)
75		return
76	}
77
78	// Move data down so we only have window size left.
79	// We know we have less than window size in b at this point.
80	discard := len(b) + len(h.b) - h.windowSize
81	copy(h.b, h.b[discard:])
82	h.b = h.b[:h.windowSize]
83	copy(h.b[h.windowSize-len(b):], b)
84}
85
86// append bytes to history without ever discarding anything.
87func (h *history) appendKeep(b []byte) {
88	h.b = append(h.b, b...)
89}
90