mirror of
https://github.com/VictoriaMetrics/VictoriaMetrics.git
synced 2024-12-15 08:23:34 +01:00
458 lines
11 KiB
Go
458 lines
11 KiB
Go
// Copyright 2016 The Snappy-Go Authors. All rights reserved.
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// Copyright (c) 2019 Klaus Post. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package s2
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import (
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"bytes"
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"encoding/binary"
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"math/bits"
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)
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func load32(b []byte, i int) uint32 {
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return binary.LittleEndian.Uint32(b[i:])
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}
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func load64(b []byte, i int) uint64 {
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return binary.LittleEndian.Uint64(b[i:])
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}
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// hash6 returns the hash of the lowest 6 bytes of u to fit in a hash table with h bits.
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// Preferably h should be a constant and should always be <64.
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func hash6(u uint64, h uint8) uint32 {
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const prime6bytes = 227718039650203
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return uint32(((u << (64 - 48)) * prime6bytes) >> ((64 - h) & 63))
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}
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func encodeGo(dst, src []byte) []byte {
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if n := MaxEncodedLen(len(src)); n < 0 {
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panic(ErrTooLarge)
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} else if len(dst) < n {
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dst = make([]byte, n)
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}
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// The block starts with the varint-encoded length of the decompressed bytes.
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d := binary.PutUvarint(dst, uint64(len(src)))
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if len(src) == 0 {
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return dst[:d]
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}
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if len(src) < minNonLiteralBlockSize {
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d += emitLiteral(dst[d:], src)
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return dst[:d]
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}
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n := encodeBlockGo(dst[d:], src)
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if n > 0 {
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d += n
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return dst[:d]
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}
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// Not compressible
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d += emitLiteral(dst[d:], src)
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return dst[:d]
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}
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// encodeBlockGo 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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//
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// len(dst) >= MaxEncodedLen(len(src)) &&
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// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
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func encodeBlockGo(dst, src []byte) (d int) {
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// Initialize the hash table.
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const (
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tableBits = 14
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maxTableSize = 1 << tableBits
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debug = false
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)
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var table [maxTableSize]uint32
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// sLimit is when to stop looking for offset/length copies. The inputMargin
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// lets us use a fast path for emitLiteral in the main loop, while we are
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// looking for copies.
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sLimit := len(src) - inputMargin
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// Bail if we can't compress to at least this.
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dstLimit := len(src) - len(src)>>5 - 5
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// nextEmit is where in src the next emitLiteral should start from.
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nextEmit := 0
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// The encoded form must start with a literal, as there are no previous
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// bytes to copy, so we start looking for hash matches at s == 1.
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s := 1
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cv := load64(src, s)
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// We search for a repeat at -1, but don't output repeats when nextEmit == 0
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repeat := 1
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for {
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candidate := 0
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for {
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// Next src position to check
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nextS := s + (s-nextEmit)>>6 + 4
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if nextS > sLimit {
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goto emitRemainder
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}
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hash0 := hash6(cv, tableBits)
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hash1 := hash6(cv>>8, tableBits)
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candidate = int(table[hash0])
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candidate2 := int(table[hash1])
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table[hash0] = uint32(s)
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table[hash1] = uint32(s + 1)
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hash2 := hash6(cv>>16, tableBits)
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// Check repeat at offset checkRep.
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const checkRep = 1
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if uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
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base := s + checkRep
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// Extend back
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for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
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i--
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base--
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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// Extend forward
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candidate := s - repeat + 4 + checkRep
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s += 4 + checkRep
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for s <= sLimit {
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if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidate += 8
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}
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if debug {
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// Validate match.
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if s <= candidate {
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panic("s <= candidate")
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}
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a := src[base:s]
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b := src[base-repeat : base-repeat+(s-base)]
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if !bytes.Equal(a, b) {
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panic("mismatch")
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}
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}
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if nextEmit > 0 {
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// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
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d += emitRepeat(dst[d:], repeat, s-base)
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} else {
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// First match, cannot be repeat.
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d += emitCopy(dst[d:], repeat, s-base)
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}
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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cv = load64(src, s)
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continue
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}
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if uint32(cv) == load32(src, candidate) {
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break
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}
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candidate = int(table[hash2])
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if uint32(cv>>8) == load32(src, candidate2) {
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table[hash2] = uint32(s + 2)
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candidate = candidate2
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s++
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break
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}
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table[hash2] = uint32(s + 2)
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if uint32(cv>>16) == load32(src, candidate) {
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s += 2
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break
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}
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cv = load64(src, nextS)
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s = nextS
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}
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// Extend backwards.
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// The top bytes will be rechecked to get the full match.
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for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
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candidate--
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s--
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}
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// Bail if we exceed the maximum size.
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if d+(s-nextEmit) > dstLimit {
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return 0
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}
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// A 4-byte match has been found. We'll later see if more than 4 bytes
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// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
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// them as literal bytes.
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d += emitLiteral(dst[d:], src[nextEmit:s])
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// Call emitCopy, and then see if another emitCopy could be our next
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// move. Repeat until we find no match for the input immediately after
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// what was consumed by the last emitCopy call.
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//
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// If we exit this loop normally then we need to call emitLiteral next,
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// though we don't yet know how big the literal will be. We handle that
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// by proceeding to the next iteration of the main loop. We also can
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// exit this loop via goto if we get close to exhausting the input.
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for {
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// Invariant: we have a 4-byte match at s, and no need to emit any
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// literal bytes prior to s.
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base := s
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repeat = base - candidate
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// Extend the 4-byte match as long as possible.
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s += 4
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candidate += 4
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for s <= len(src)-8 {
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if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidate += 8
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}
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d += emitCopy(dst[d:], repeat, s-base)
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if debug {
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// Validate match.
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if s <= candidate {
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panic("s <= candidate")
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}
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a := src[base:s]
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b := src[base-repeat : base-repeat+(s-base)]
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if !bytes.Equal(a, b) {
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panic("mismatch")
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}
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}
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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if d > dstLimit {
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// Do we have space for more, if not bail.
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return 0
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}
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// Check for an immediate match, otherwise start search at s+1
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x := load64(src, s-2)
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m2Hash := hash6(x, tableBits)
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currHash := hash6(x>>16, tableBits)
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candidate = int(table[currHash])
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table[m2Hash] = uint32(s - 2)
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table[currHash] = uint32(s)
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if debug && s == candidate {
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panic("s == candidate")
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}
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if uint32(x>>16) != load32(src, candidate) {
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cv = load64(src, s+1)
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s++
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break
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}
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}
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}
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emitRemainder:
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if nextEmit < len(src) {
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// Bail if we exceed the maximum size.
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if d+len(src)-nextEmit > dstLimit {
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return 0
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}
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d += emitLiteral(dst[d:], src[nextEmit:])
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}
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return d
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}
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func encodeBlockSnappyGo(dst, src []byte) (d int) {
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// Initialize the hash table.
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const (
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tableBits = 14
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maxTableSize = 1 << tableBits
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)
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var table [maxTableSize]uint32
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// sLimit is when to stop looking for offset/length copies. The inputMargin
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// lets us use a fast path for emitLiteral in the main loop, while we are
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// looking for copies.
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sLimit := len(src) - inputMargin
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// Bail if we can't compress to at least this.
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dstLimit := len(src) - len(src)>>5 - 5
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// nextEmit is where in src the next emitLiteral should start from.
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nextEmit := 0
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// The encoded form must start with a literal, as there are no previous
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// bytes to copy, so we start looking for hash matches at s == 1.
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s := 1
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cv := load64(src, s)
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// We search for a repeat at -1, but don't output repeats when nextEmit == 0
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repeat := 1
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for {
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candidate := 0
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for {
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// Next src position to check
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nextS := s + (s-nextEmit)>>6 + 4
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if nextS > sLimit {
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goto emitRemainder
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}
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hash0 := hash6(cv, tableBits)
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hash1 := hash6(cv>>8, tableBits)
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candidate = int(table[hash0])
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candidate2 := int(table[hash1])
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table[hash0] = uint32(s)
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table[hash1] = uint32(s + 1)
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hash2 := hash6(cv>>16, tableBits)
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// Check repeat at offset checkRep.
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const checkRep = 1
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if uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
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base := s + checkRep
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// Extend back
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for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
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i--
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base--
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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// Extend forward
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candidate := s - repeat + 4 + checkRep
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s += 4 + checkRep
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for s <= sLimit {
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if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidate += 8
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}
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d += emitCopyNoRepeat(dst[d:], repeat, s-base)
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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cv = load64(src, s)
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continue
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}
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if uint32(cv) == load32(src, candidate) {
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break
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}
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candidate = int(table[hash2])
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if uint32(cv>>8) == load32(src, candidate2) {
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table[hash2] = uint32(s + 2)
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candidate = candidate2
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s++
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break
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}
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table[hash2] = uint32(s + 2)
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if uint32(cv>>16) == load32(src, candidate) {
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s += 2
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break
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}
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cv = load64(src, nextS)
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s = nextS
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}
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// Extend backwards
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for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
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candidate--
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s--
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}
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// Bail if we exceed the maximum size.
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if d+(s-nextEmit) > dstLimit {
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return 0
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}
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// A 4-byte match has been found. We'll later see if more than 4 bytes
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// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
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// them as literal bytes.
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d += emitLiteral(dst[d:], src[nextEmit:s])
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// Call emitCopy, and then see if another emitCopy could be our next
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// move. Repeat until we find no match for the input immediately after
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// what was consumed by the last emitCopy call.
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//
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// If we exit this loop normally then we need to call emitLiteral next,
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// though we don't yet know how big the literal will be. We handle that
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// by proceeding to the next iteration of the main loop. We also can
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// exit this loop via goto if we get close to exhausting the input.
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for {
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// Invariant: we have a 4-byte match at s, and no need to emit any
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// literal bytes prior to s.
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base := s
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repeat = base - candidate
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// Extend the 4-byte match as long as possible.
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s += 4
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candidate += 4
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for s <= len(src)-8 {
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if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidate += 8
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}
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d += emitCopyNoRepeat(dst[d:], repeat, s-base)
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if false {
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// Validate match.
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a := src[base:s]
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b := src[base-repeat : base-repeat+(s-base)]
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if !bytes.Equal(a, b) {
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panic("mismatch")
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}
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}
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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if d > dstLimit {
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// Do we have space for more, if not bail.
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return 0
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}
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// Check for an immediate match, otherwise start search at s+1
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x := load64(src, s-2)
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m2Hash := hash6(x, tableBits)
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currHash := hash6(x>>16, tableBits)
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candidate = int(table[currHash])
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table[m2Hash] = uint32(s - 2)
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table[currHash] = uint32(s)
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if uint32(x>>16) != load32(src, candidate) {
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cv = load64(src, s+1)
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s++
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break
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}
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}
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}
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emitRemainder:
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if nextEmit < len(src) {
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// Bail if we exceed the maximum size.
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if d+len(src)-nextEmit > dstLimit {
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return 0
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}
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d += emitLiteral(dst[d:], src[nextEmit:])
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}
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return d
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}
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