30802fac73
zstd is a compression algorithm that has a very fast decoder, while providing also good compression ratios. The fast decoder makes it suitable for container images, as decompressing the tarballs is a very expensive operation. https://github.com/opencontainers/image-spec/pull/788 added support for zstd to the OCI image specs. Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
90 lines
2.3 KiB
Go
90 lines
2.3 KiB
Go
// Copyright 2019+ Klaus Post. All rights reserved.
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// License information can be found in the LICENSE file.
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// Based on work by Yann Collet, released under BSD License.
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package zstd
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import (
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"github.com/klauspost/compress/huff0"
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)
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// history contains the information transferred between blocks.
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type history struct {
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b []byte
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huffTree *huff0.Scratch
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recentOffsets [3]int
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decoders sequenceDecs
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windowSize int
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maxSize int
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error bool
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dict *dict
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}
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// reset will reset the history to initial state of a frame.
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// The history must already have been initialized to the desired size.
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func (h *history) reset() {
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h.b = h.b[:0]
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h.error = false
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h.recentOffsets = [3]int{1, 4, 8}
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if f := h.decoders.litLengths.fse; f != nil && !f.preDefined {
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fseDecoderPool.Put(f)
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}
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if f := h.decoders.offsets.fse; f != nil && !f.preDefined {
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fseDecoderPool.Put(f)
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}
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if f := h.decoders.matchLengths.fse; f != nil && !f.preDefined {
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fseDecoderPool.Put(f)
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}
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h.decoders = sequenceDecs{}
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if h.huffTree != nil {
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if h.dict == nil || h.dict.litEnc != h.huffTree {
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huffDecoderPool.Put(h.huffTree)
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}
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}
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h.huffTree = nil
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h.dict = nil
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//printf("history created: %+v (l: %d, c: %d)", *h, len(h.b), cap(h.b))
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}
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func (h *history) setDict(dict *dict) {
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if dict == nil {
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return
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}
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h.dict = dict
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h.decoders.litLengths = dict.llDec
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h.decoders.offsets = dict.ofDec
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h.decoders.matchLengths = dict.mlDec
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h.recentOffsets = dict.offsets
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h.huffTree = dict.litEnc
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}
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// append bytes to history.
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// This function will make sure there is space for it,
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// if the buffer has been allocated with enough extra space.
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func (h *history) append(b []byte) {
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if len(b) >= h.windowSize {
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// Discard all history by simply overwriting
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h.b = h.b[:h.windowSize]
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copy(h.b, b[len(b)-h.windowSize:])
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return
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}
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// If there is space, append it.
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if len(b) < cap(h.b)-len(h.b) {
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h.b = append(h.b, b...)
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return
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}
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// Move data down so we only have window size left.
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// We know we have less than window size in b at this point.
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discard := len(b) + len(h.b) - h.windowSize
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copy(h.b, h.b[discard:])
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h.b = h.b[:h.windowSize]
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copy(h.b[h.windowSize-len(b):], b)
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}
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// append bytes to history without ever discarding anything.
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func (h *history) appendKeep(b []byte) {
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h.b = append(h.b, b...)
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}
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