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115 lines
2.9 KiB
115 lines
2.9 KiB
// 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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"fmt"
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"io"
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"math"
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"math/bits"
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)
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type frameHeader struct {
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ContentSize uint64
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WindowSize uint32
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SingleSegment bool
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Checksum bool
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DictID uint32 // Not stored.
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}
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const maxHeaderSize = 14
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func (f frameHeader) appendTo(dst []byte) ([]byte, error) {
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dst = append(dst, frameMagic...)
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var fhd uint8
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if f.Checksum {
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fhd |= 1 << 2
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}
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if f.SingleSegment {
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fhd |= 1 << 5
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}
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var fcs uint8
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if f.ContentSize >= 256 {
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fcs++
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}
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if f.ContentSize >= 65536+256 {
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fcs++
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}
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if f.ContentSize >= 0xffffffff {
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fcs++
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}
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fhd |= fcs << 6
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dst = append(dst, fhd)
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if !f.SingleSegment {
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const winLogMin = 10
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windowLog := (bits.Len32(f.WindowSize-1) - winLogMin) << 3
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dst = append(dst, uint8(windowLog))
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}
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switch fcs {
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case 0:
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if f.SingleSegment {
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dst = append(dst, uint8(f.ContentSize))
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}
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// Unless SingleSegment is set, framessizes < 256 are nto stored.
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case 1:
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f.ContentSize -= 256
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dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8))
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case 2:
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dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8), uint8(f.ContentSize>>16), uint8(f.ContentSize>>24))
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case 3:
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dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8), uint8(f.ContentSize>>16), uint8(f.ContentSize>>24),
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uint8(f.ContentSize>>32), uint8(f.ContentSize>>40), uint8(f.ContentSize>>48), uint8(f.ContentSize>>56))
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default:
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panic("invalid fcs")
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}
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return dst, nil
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}
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const skippableFrameHeader = 4 + 4
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// calcSkippableFrame will return a total size to be added for written
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// to be divisible by multiple.
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// The value will always be > skippableFrameHeader.
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// The function will panic if written < 0 or wantMultiple <= 0.
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func calcSkippableFrame(written, wantMultiple int64) int {
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if wantMultiple <= 0 {
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panic("wantMultiple <= 0")
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}
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if written < 0 {
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panic("written < 0")
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}
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leftOver := written % wantMultiple
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if leftOver == 0 {
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return 0
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}
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toAdd := wantMultiple - leftOver
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for toAdd < skippableFrameHeader {
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toAdd += wantMultiple
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}
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return int(toAdd)
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}
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// skippableFrame will add a skippable frame with a total size of bytes.
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// total should be >= skippableFrameHeader and < math.MaxUint32.
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func skippableFrame(dst []byte, total int, r io.Reader) ([]byte, error) {
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if total == 0 {
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return dst, nil
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}
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if total < skippableFrameHeader {
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return dst, fmt.Errorf("requested skippable frame (%d) < 8", total)
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}
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if int64(total) > math.MaxUint32 {
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return dst, fmt.Errorf("requested skippable frame (%d) > max uint32", total)
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}
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dst = append(dst, 0x50, 0x2a, 0x4d, 0x18)
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f := uint32(total - skippableFrameHeader)
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dst = append(dst, uint8(f), uint8(f>>8), uint8(f>>16), uint8(f>>24))
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start := len(dst)
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dst = append(dst, make([]byte, f)...)
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_, err := io.ReadFull(r, dst[start:])
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return dst, err
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}
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