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// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.
package zstd
import "math/bits"
type seqCoders struct {
llEnc, ofEnc, mlEnc *fseEncoder
llPrev, ofPrev, mlPrev *fseEncoder
}
// swap coders with another (block).
func (s *seqCoders) swap(other *seqCoders) {
*s, *other = *other, *s
}
// setPrev will update the previous encoders to the actually used ones
// and make sure a fresh one is in the main slot.
func (s *seqCoders) setPrev(ll, ml, of *fseEncoder) {
compareSwap := func(used *fseEncoder, current, prev **fseEncoder) {
// We used the new one, more current to history and reuse the previous history
if *current == used {
*prev, *current = *current, *prev
c := *current
p := *prev
c.reUsed = false
p.reUsed = true
return
}
if used == *prev {
return
}
// Ensure we cannot reuse by accident
prevEnc := *prev
prevEnc.symbolLen = 0
return
}
compareSwap(ll, &s.llEnc, &s.llPrev)
compareSwap(ml, &s.mlEnc, &s.mlPrev)
compareSwap(of, &s.ofEnc, &s.ofPrev)
}
func highBit(val uint32) (n uint32) {
return uint32(bits.Len32(val) - 1)
}
var llCodeTable = [64]byte{0, 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12, 13, 14, 15,
16, 16, 17, 17, 18, 18, 19, 19,
20, 20, 20, 20, 21, 21, 21, 21,
22, 22, 22, 22, 22, 22, 22, 22,
23, 23, 23, 23, 23, 23, 23, 23,
24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24}
// Up to 6 bits
const maxLLCode = 35
// llBitsTable translates from ll code to number of bits.
var llBitsTable = [maxLLCode + 1]byte{
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 2, 2, 3, 3,
4, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16}
// llCode returns the code that represents the literal length requested.
func llCode(litLength uint32) uint8 {
const llDeltaCode = 19
if litLength <= 63 {
// Compiler insists on bounds check (Go 1.12)
return llCodeTable[litLength&63]
}
return uint8(highBit(litLength)) + llDeltaCode
}
var mlCodeTable = [128]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 36, 36, 37, 37, 37, 37,
38, 38, 38, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 39, 39, 39,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42}
// Up to 6 bits
const maxMLCode = 52
// mlBitsTable translates from ml code to number of bits.
var mlBitsTable = [maxMLCode + 1]byte{
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 2, 2, 3, 3,
4, 4, 5, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16}
// note : mlBase = matchLength - MINMATCH;
// because it's the format it's stored in seqStore->sequences
func mlCode(mlBase uint32) uint8 {
const mlDeltaCode = 36
if mlBase <= 127 {
// Compiler insists on bounds check (Go 1.12)
return mlCodeTable[mlBase&127]
}
return uint8(highBit(mlBase)) + mlDeltaCode
}
func ofCode(offset uint32) uint8 {
// A valid offset will always be > 0.
return uint8(bits.Len32(offset) - 1)
}
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