299 lines
7.4 KiB
Go
299 lines
7.4 KiB
Go
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//go:build !amd64 || appengine || !gc || noasm
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// +build !amd64 appengine !gc noasm
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package s2
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import (
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"math/bits"
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)
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// encodeBlock encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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// len(dst) >= MaxEncodedLen(len(src))
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func encodeBlock(dst, src []byte) (d int) {
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if len(src) < minNonLiteralBlockSize {
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return 0
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}
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return encodeBlockGo(dst, src)
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}
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// encodeBlockBetter encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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// len(dst) >= MaxEncodedLen(len(src))
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func encodeBlockBetter(dst, src []byte) (d int) {
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return encodeBlockBetterGo(dst, src)
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}
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// encodeBlockBetter encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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// len(dst) >= MaxEncodedLen(len(src))
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func encodeBlockBetterSnappy(dst, src []byte) (d int) {
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return encodeBlockBetterSnappyGo(dst, src)
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}
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// encodeBlock encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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// len(dst) >= MaxEncodedLen(len(src))
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func encodeBlockSnappy(dst, src []byte) (d int) {
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if len(src) < minNonLiteralBlockSize {
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return 0
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}
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return encodeBlockSnappyGo(dst, src)
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}
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// emitLiteral writes a literal chunk and returns the number of bytes written.
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//
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// It assumes that:
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// dst is long enough to hold the encoded bytes
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// 0 <= len(lit) && len(lit) <= math.MaxUint32
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func emitLiteral(dst, lit []byte) int {
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if len(lit) == 0 {
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return 0
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}
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const num = 63<<2 | tagLiteral
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i, n := 0, uint(len(lit)-1)
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switch {
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case n < 60:
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dst[0] = uint8(n)<<2 | tagLiteral
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i = 1
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case n < 1<<8:
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dst[1] = uint8(n)
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dst[0] = 60<<2 | tagLiteral
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i = 2
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case n < 1<<16:
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dst[2] = uint8(n >> 8)
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dst[1] = uint8(n)
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dst[0] = 61<<2 | tagLiteral
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i = 3
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case n < 1<<24:
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dst[3] = uint8(n >> 16)
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dst[2] = uint8(n >> 8)
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dst[1] = uint8(n)
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dst[0] = 62<<2 | tagLiteral
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i = 4
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default:
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dst[4] = uint8(n >> 24)
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dst[3] = uint8(n >> 16)
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dst[2] = uint8(n >> 8)
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dst[1] = uint8(n)
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dst[0] = 63<<2 | tagLiteral
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i = 5
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}
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return i + copy(dst[i:], lit)
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}
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// emitRepeat writes a repeat chunk and returns the number of bytes written.
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// Length must be at least 4 and < 1<<24
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func emitRepeat(dst []byte, offset, length int) int {
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// Repeat offset, make length cheaper
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length -= 4
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if length <= 4 {
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dst[0] = uint8(length)<<2 | tagCopy1
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dst[1] = 0
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return 2
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}
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if length < 8 && offset < 2048 {
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// Encode WITH offset
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dst[1] = uint8(offset)
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dst[0] = uint8(offset>>8)<<5 | uint8(length)<<2 | tagCopy1
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return 2
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}
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if length < (1<<8)+4 {
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length -= 4
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dst[2] = uint8(length)
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dst[1] = 0
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dst[0] = 5<<2 | tagCopy1
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return 3
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}
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if length < (1<<16)+(1<<8) {
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length -= 1 << 8
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dst[3] = uint8(length >> 8)
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dst[2] = uint8(length >> 0)
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dst[1] = 0
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dst[0] = 6<<2 | tagCopy1
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return 4
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}
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const maxRepeat = (1 << 24) - 1
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length -= 1 << 16
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left := 0
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if length > maxRepeat {
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left = length - maxRepeat + 4
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length = maxRepeat - 4
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}
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dst[4] = uint8(length >> 16)
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dst[3] = uint8(length >> 8)
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dst[2] = uint8(length >> 0)
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dst[1] = 0
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dst[0] = 7<<2 | tagCopy1
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if left > 0 {
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return 5 + emitRepeat(dst[5:], offset, left)
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}
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return 5
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}
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// emitCopy writes a copy chunk and returns the number of bytes written.
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//
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// It assumes that:
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// dst is long enough to hold the encoded bytes
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// 1 <= offset && offset <= math.MaxUint32
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// 4 <= length && length <= 1 << 24
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func emitCopy(dst []byte, offset, length int) int {
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if offset >= 65536 {
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i := 0
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if length > 64 {
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// Emit a length 64 copy, encoded as 5 bytes.
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dst[4] = uint8(offset >> 24)
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dst[3] = uint8(offset >> 16)
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = 63<<2 | tagCopy4
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length -= 64
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if length >= 4 {
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// Emit remaining as repeats
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return 5 + emitRepeat(dst[5:], offset, length)
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}
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i = 5
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}
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if length == 0 {
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return i
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}
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// Emit a copy, offset encoded as 4 bytes.
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dst[i+0] = uint8(length-1)<<2 | tagCopy4
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dst[i+1] = uint8(offset)
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dst[i+2] = uint8(offset >> 8)
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dst[i+3] = uint8(offset >> 16)
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dst[i+4] = uint8(offset >> 24)
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return i + 5
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}
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// Offset no more than 2 bytes.
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if length > 64 {
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// Emit a length 60 copy, encoded as 3 bytes.
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// Emit remaining as repeat value (minimum 4 bytes).
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = 59<<2 | tagCopy2
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length -= 60
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// Emit remaining as repeats, at least 4 bytes remain.
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return 3 + emitRepeat(dst[3:], offset, length)
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}
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if length >= 12 || offset >= 2048 {
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// Emit the remaining copy, encoded as 3 bytes.
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = uint8(length-1)<<2 | tagCopy2
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return 3
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}
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// Emit the remaining copy, encoded as 2 bytes.
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dst[1] = uint8(offset)
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dst[0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1
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return 2
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}
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// emitCopyNoRepeat writes a copy chunk and returns the number of bytes written.
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//
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// It assumes that:
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// dst is long enough to hold the encoded bytes
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// 1 <= offset && offset <= math.MaxUint32
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// 4 <= length && length <= 1 << 24
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func emitCopyNoRepeat(dst []byte, offset, length int) int {
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if offset >= 65536 {
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i := 0
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if length > 64 {
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// Emit a length 64 copy, encoded as 5 bytes.
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dst[4] = uint8(offset >> 24)
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dst[3] = uint8(offset >> 16)
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = 63<<2 | tagCopy4
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length -= 64
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if length >= 4 {
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// Emit remaining as repeats
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return 5 + emitCopyNoRepeat(dst[5:], offset, length)
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}
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i = 5
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}
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if length == 0 {
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return i
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}
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// Emit a copy, offset encoded as 4 bytes.
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dst[i+0] = uint8(length-1)<<2 | tagCopy4
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dst[i+1] = uint8(offset)
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dst[i+2] = uint8(offset >> 8)
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dst[i+3] = uint8(offset >> 16)
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dst[i+4] = uint8(offset >> 24)
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return i + 5
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}
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// Offset no more than 2 bytes.
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if length > 64 {
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// Emit a length 60 copy, encoded as 3 bytes.
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// Emit remaining as repeat value (minimum 4 bytes).
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = 59<<2 | tagCopy2
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length -= 60
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// Emit remaining as repeats, at least 4 bytes remain.
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return 3 + emitCopyNoRepeat(dst[3:], offset, length)
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}
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if length >= 12 || offset >= 2048 {
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// Emit the remaining copy, encoded as 3 bytes.
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dst[2] = uint8(offset >> 8)
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dst[1] = uint8(offset)
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dst[0] = uint8(length-1)<<2 | tagCopy2
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return 3
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}
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// Emit the remaining copy, encoded as 2 bytes.
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dst[1] = uint8(offset)
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dst[0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1
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return 2
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}
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// matchLen returns how many bytes match in a and b
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//
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// It assumes that:
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// len(a) <= len(b)
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//
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func matchLen(a []byte, b []byte) int {
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b = b[:len(a)]
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var checked int
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if len(a) > 4 {
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// Try 4 bytes first
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if diff := load32(a, 0) ^ load32(b, 0); diff != 0 {
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return bits.TrailingZeros32(diff) >> 3
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}
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// Switch to 8 byte matching.
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checked = 4
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a = a[4:]
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b = b[4:]
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for len(a) >= 8 {
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b = b[:len(a)]
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if diff := load64(a, 0) ^ load64(b, 0); diff != 0 {
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return checked + (bits.TrailingZeros64(diff) >> 3)
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}
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checked += 8
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a = a[8:]
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b = b[8:]
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}
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}
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b = b[:len(a)]
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for i := range a {
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if a[i] != b[i] {
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return int(i) + checked
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}
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}
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return len(a) + checked
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}
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