1097 lines
22 KiB
Go
1097 lines
22 KiB
Go
package rardecode
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import (
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"errors"
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"io"
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)
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const (
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rangeBottom = 1 << 15
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rangeTop = 1 << 24
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maxFreq = 124
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intBits = 7
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periodBits = 7
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binScale = 1 << (intBits + periodBits)
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n0 = 1
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n1 = 4
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n2 = 4
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n3 = 4
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n4 = (128 + 3 - 1*n1 - 2*n2 - 3*n3) / 4
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nIndexes = n0 + n1 + n2 + n3 + n4
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// memory is allocated in units. A unit contains unitSize number of bytes.
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// A unit can store one context or two states.
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unitSize = 12
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maxUint16 = 1<<16 - 1
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freeMark = -1
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)
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var (
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errCorruptPPM = errors.New("rardecode: corrupt ppm data")
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expEscape = []byte{25, 14, 9, 7, 5, 5, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2}
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initBinEsc = []uint16{0x3CDD, 0x1F3F, 0x59BF, 0x48F3, 0x64A1, 0x5ABC, 0x6632, 0x6051}
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ns2Index [256]byte
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ns2BSIndex [256]byte
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// units2Index maps the number of units in a block to a freelist index
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units2Index [128 + 1]byte
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// index2Units maps a freelist index to the size of the block in units
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index2Units [nIndexes]int32
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)
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func init() {
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ns2BSIndex[0] = 2 * 0
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ns2BSIndex[1] = 2 * 1
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for i := 2; i < 11; i++ {
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ns2BSIndex[i] = 2 * 2
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}
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for i := 11; i < 256; i++ {
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ns2BSIndex[i] = 2 * 3
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}
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var j, n byte
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for i := range ns2Index {
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ns2Index[i] = n
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if j <= 3 {
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n++
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j = n
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} else {
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j--
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}
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}
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var ii byte
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var iu, units int32
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for i, n := range []int{n0, n1, n2, n3, n4} {
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for j := 0; j < n; j++ {
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units += int32(i)
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index2Units[ii] = units
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for iu <= units {
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units2Index[iu] = ii
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iu++
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}
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ii++
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}
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}
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}
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type rangeCoder struct {
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br io.ByteReader
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code uint32
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low uint32
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rnge uint32
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}
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func (r *rangeCoder) init(br io.ByteReader) error {
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r.br = br
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r.low = 0
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r.rnge = ^uint32(0)
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for i := 0; i < 4; i++ {
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c, err := r.br.ReadByte()
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if err != nil {
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return err
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}
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r.code = r.code<<8 | uint32(c)
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}
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return nil
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}
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func (r *rangeCoder) currentCount(scale uint32) uint32 {
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r.rnge /= scale
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return (r.code - r.low) / r.rnge
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}
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func (r *rangeCoder) normalize() error {
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for {
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if r.low^(r.low+r.rnge) >= rangeTop {
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if r.rnge >= rangeBottom {
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return nil
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}
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r.rnge = -r.low & (rangeBottom - 1)
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}
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c, err := r.br.ReadByte()
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if err != nil {
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return err
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}
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r.code = r.code<<8 | uint32(c)
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r.rnge <<= 8
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r.low <<= 8
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}
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}
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func (r *rangeCoder) decode(lowCount, highCount uint32) error {
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r.low += r.rnge * lowCount
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r.rnge *= highCount - lowCount
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return r.normalize()
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}
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type see2Context struct {
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summ uint16
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shift byte
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count byte
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}
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func newSee2Context(i uint16) see2Context {
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return see2Context{i << (periodBits - 4), (periodBits - 4), 4}
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}
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func (s *see2Context) mean() uint32 {
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if s == nil {
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return 1
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}
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n := s.summ >> s.shift
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if n == 0 {
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return 1
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}
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s.summ -= n
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return uint32(n)
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}
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func (s *see2Context) update() {
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if s == nil || s.shift >= periodBits {
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return
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}
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s.count--
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if s.count == 0 {
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s.summ += s.summ
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s.count = 3 << s.shift
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s.shift++
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}
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}
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type state struct {
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sym byte
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freq byte
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// succ can point to a context or byte in memory.
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// A context pointer is a positive integer. It is an index into the states
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// array that points to the first of two states which the context is
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// marshalled into.
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// A byte pointer is a negative integer. The magnitude represents the position
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// in bytes from the bottom of the memory. As memory is modelled as an array of
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// states, this is used to calculate which state, and where in the state the
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// byte is stored.
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// A zero value represents a nil pointer.
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succ int32
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}
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// uint16 return a uint16 stored in the sym and freq fields of a state
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func (s state) uint16() uint16 { return uint16(s.sym) | uint16(s.freq)<<8 }
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// setUint16 stores a uint16 in the sym and freq fields of a state
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func (s *state) setUint16(n uint16) { s.sym = byte(n); s.freq = byte(n >> 8) }
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// A context is marshalled into a slice of two states.
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// The first state contains the number of states, and the suffix pointer.
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// If there is only one state, the second state contains that state.
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// If there is more than one state, the second state contains the summFreq
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// and the index to the slice of states.
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type context struct {
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i int32 // index into the states array for context
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s []state // slice of two states representing context
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a *subAllocator
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}
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// succPtr returns a pointer value for the context to be stored in a state.succ
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func (c *context) succPtr() int32 { return c.i }
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func (c *context) numStates() int { return int(c.s[0].uint16()) }
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func (c *context) setNumStates(n int) { c.s[0].setUint16(uint16(n)) }
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func (c *context) statesIndex() int32 { return c.s[1].succ }
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func (c *context) setStatesIndex(n int32) { c.s[1].succ = n }
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func (c *context) suffix() *context { return c.a.succContext(c.s[0].succ) }
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func (c *context) setSuffix(sc *context) { c.s[0].succ = sc.i }
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func (c *context) summFreq() uint16 { return c.s[1].uint16() }
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func (c *context) setSummFreq(f uint16) { c.s[1].setUint16(f) }
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func (c *context) notEq(ctx *context) bool { return c.i != ctx.i }
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func (c *context) states() []state {
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if ns := int32(c.s[0].uint16()); ns != 1 {
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i := c.s[1].succ
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return c.a.states[i : i+ns]
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}
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return c.s[1:]
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}
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// shrinkStates shrinks the state list down to size states
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func (c *context) shrinkStates(states []state, size int) []state {
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i1 := units2Index[(len(states)+1)>>1]
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i2 := units2Index[(size+1)>>1]
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if size == 1 {
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// store state in context, and free states block
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n := c.statesIndex()
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c.s[1] = states[0]
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states = c.s[1:]
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c.a.addFreeBlock(n, i1)
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} else if i1 != i2 {
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if n := c.a.removeFreeBlock(i2); n > 0 {
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// allocate new block and copy
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copy(c.a.states[n:], states[:size])
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states = c.a.states[n:]
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// free old block
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c.a.addFreeBlock(c.statesIndex(), i1)
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c.setStatesIndex(n)
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} else {
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// split current block, and free units not needed
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n = c.statesIndex() + index2Units[i2]<<1
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u := index2Units[i1] - index2Units[i2]
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c.a.freeUnits(n, u)
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}
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}
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c.setNumStates(size)
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return states[:size]
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}
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// expandStates expands the states list by one
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func (c *context) expandStates() []state {
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states := c.states()
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ns := len(states)
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if ns == 1 {
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s := states[0]
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n := c.a.allocUnits(1)
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if n == 0 {
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return nil
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}
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c.setStatesIndex(n)
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states = c.a.states[n:]
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states[0] = s
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} else if ns&0x1 == 0 {
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u := ns >> 1
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i1 := units2Index[u]
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i2 := units2Index[u+1]
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if i1 != i2 {
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n := c.a.allocUnits(i2)
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if n == 0 {
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return nil
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}
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copy(c.a.states[n:], states)
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c.a.addFreeBlock(c.statesIndex(), i1)
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c.setStatesIndex(n)
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states = c.a.states[n:]
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}
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}
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c.setNumStates(ns + 1)
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return states[:ns+1]
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}
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type subAllocator struct {
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// memory for allocation is split into two heaps
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heap1MaxBytes int32 // maximum bytes available in heap1
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heap1Lo int32 // heap1 bottom in number of bytes
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heap1Hi int32 // heap1 top in number of bytes
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heap2Lo int32 // heap2 bottom index in states
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heap2Hi int32 // heap2 top index in states
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glueCount int
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// Each freeList entry contains an index into states for the beginning
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// of a free block. The first state in that block may contain an index
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// to another free block and so on. The size of the free block in units
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// (2 states) for that freeList index can be determined from the
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// index2Units array.
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freeList [nIndexes]int32
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// Instead of bytes, memory is represented by a slice of states.
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// context's are marshalled to and from a pair of states.
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// multiple bytes are stored in a state.
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states []state
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}
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func (a *subAllocator) init(maxMB int) {
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bytes := int32(maxMB) << 20
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heap2Units := bytes / 8 / unitSize * 7
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a.heap1MaxBytes = bytes - heap2Units*unitSize
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// Add one for the case when bytes are not a multiple of unitSize
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heap1Units := a.heap1MaxBytes/unitSize + 1
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// Calculate total size in state's. Add 1 unit so we can reserve the first unit.
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// This will allow us to use the zero index as a nil pointer.
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n := int(1+heap1Units+heap2Units) * 2
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if cap(a.states) > n {
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a.states = a.states[:n]
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} else {
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a.states = make([]state, n)
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}
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}
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func (a *subAllocator) restart() {
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// Pad heap1 start by 1 unit and enough bytes so that there is no
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// gap between heap1 end and heap2 start.
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a.heap1Lo = unitSize + (unitSize - a.heap1MaxBytes%unitSize)
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a.heap1Hi = unitSize + (a.heap1MaxBytes/unitSize+1)*unitSize
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a.heap2Lo = a.heap1Hi / unitSize * 2
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a.heap2Hi = int32(len(a.states))
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a.glueCount = 0
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for i := range a.freeList {
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a.freeList[i] = 0
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}
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for i := range a.states {
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a.states[i] = state{}
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}
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}
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// pushByte puts a byte on the heap and returns a state.succ index that
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// can be used to retrieve it.
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func (a *subAllocator) pushByte(c byte) int32 {
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si := a.heap1Lo / 6 // state index
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oi := a.heap1Lo % 6 // byte position in state
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switch oi {
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case 0:
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a.states[si].sym = c
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case 1:
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a.states[si].freq = c
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default:
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n := (uint(oi) - 2) * 8
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mask := ^(uint32(0xFF) << n)
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succ := uint32(a.states[si].succ) & mask
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succ |= uint32(c) << n
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a.states[si].succ = int32(succ)
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}
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a.heap1Lo++
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if a.heap1Lo >= a.heap1Hi {
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return 0
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}
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return -a.heap1Lo
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}
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// popByte reverses the previous pushByte
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func (a *subAllocator) popByte() { a.heap1Lo-- }
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// succByte returns a byte from the heap given a state.succ index
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func (a *subAllocator) succByte(i int32) byte {
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i = -i
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si := i / 6
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oi := i % 6
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switch oi {
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case 0:
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return a.states[si].sym
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case 1:
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return a.states[si].freq
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default:
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n := (uint(oi) - 2) * 8
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succ := uint32(a.states[si].succ) >> n
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return byte(succ & 0xff)
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}
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}
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// succContext returns a context given a state.succ index
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func (a *subAllocator) succContext(i int32) *context {
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if i <= 0 {
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return nil
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}
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return &context{i: i, s: a.states[i : i+2 : i+2], a: a}
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}
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// succIsNil returns whether a state.succ points to nothing
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func (a *subAllocator) succIsNil(i int32) bool { return i == 0 }
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|
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// nextByteAddr takes a state.succ value representing a pointer
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// to a byte, and returns the next bytes address
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func (a *subAllocator) nextByteAddr(n int32) int32 { return n - 1 }
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func (a *subAllocator) removeFreeBlock(i byte) int32 {
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n := a.freeList[i]
|
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if n != 0 {
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a.freeList[i] = a.states[n].succ
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a.states[n] = state{}
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}
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return n
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}
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func (a *subAllocator) addFreeBlock(n int32, i byte) {
|
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a.states[n].succ = a.freeList[i]
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a.freeList[i] = n
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}
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|
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func (a *subAllocator) freeUnits(n, u int32) {
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i := units2Index[u]
|
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if u != index2Units[i] {
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i--
|
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a.addFreeBlock(n, i)
|
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u -= index2Units[i]
|
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n += index2Units[i] << 1
|
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i = units2Index[u]
|
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}
|
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a.addFreeBlock(n, i)
|
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}
|
|
|
|
func (a *subAllocator) glueFreeBlocks() {
|
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var freeIndex int32
|
|
|
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for i, n := range a.freeList {
|
|
s := state{succ: freeMark}
|
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s.setUint16(uint16(index2Units[i]))
|
|
for n != 0 {
|
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states := a.states[n:]
|
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states[1].succ = freeIndex
|
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freeIndex = n
|
|
n = states[0].succ
|
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states[0] = s
|
|
}
|
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a.freeList[i] = 0
|
|
}
|
|
|
|
for i := freeIndex; i != 0; i = a.states[i+1].succ {
|
|
if a.states[i].succ != freeMark {
|
|
continue
|
|
}
|
|
u := int32(a.states[i].uint16())
|
|
states := a.states[i+u<<1:]
|
|
for len(states) > 0 && states[0].succ == freeMark {
|
|
u += int32(states[0].uint16())
|
|
if u > maxUint16 {
|
|
break
|
|
}
|
|
states[0].succ = 0
|
|
a.states[i].setUint16(uint16(u))
|
|
states = a.states[i+u<<1:]
|
|
}
|
|
}
|
|
|
|
for n := freeIndex; n != 0; n = a.states[n+1].succ {
|
|
if a.states[n].succ != freeMark {
|
|
continue
|
|
}
|
|
a.states[n].succ = 0
|
|
u := int32(a.states[n].uint16())
|
|
m := n
|
|
for u > 128 {
|
|
a.addFreeBlock(m, nIndexes-1)
|
|
u -= 128
|
|
m += 256
|
|
}
|
|
a.freeUnits(m, u)
|
|
}
|
|
}
|
|
|
|
func (a *subAllocator) allocUnitsRare(index byte) int32 {
|
|
if a.glueCount == 0 {
|
|
a.glueCount = 255
|
|
a.glueFreeBlocks()
|
|
if n := a.removeFreeBlock(index); n > 0 {
|
|
return n
|
|
}
|
|
}
|
|
// try to find a larger free block and split it
|
|
for i := index + 1; i < nIndexes; i++ {
|
|
if n := a.removeFreeBlock(i); n > 0 {
|
|
u := index2Units[i] - index2Units[index]
|
|
a.freeUnits(n+index2Units[index]<<1, u)
|
|
return n
|
|
}
|
|
}
|
|
a.glueCount--
|
|
|
|
// try to allocate units from the top of heap1
|
|
n := a.heap1Hi - index2Units[index]*unitSize
|
|
if n > a.heap1Lo {
|
|
a.heap1Hi = n
|
|
return a.heap1Hi / unitSize * 2
|
|
}
|
|
return 0
|
|
}
|
|
|
|
func (a *subAllocator) allocUnits(i byte) int32 {
|
|
// try to allocate a free block
|
|
if n := a.removeFreeBlock(i); n > 0 {
|
|
return n
|
|
}
|
|
// try to allocate from the bottom of heap2
|
|
n := index2Units[i] << 1
|
|
if a.heap2Lo+n <= a.heap2Hi {
|
|
lo := a.heap2Lo
|
|
a.heap2Lo += n
|
|
return lo
|
|
}
|
|
return a.allocUnitsRare(i)
|
|
}
|
|
|
|
func (a *subAllocator) newContext(s state, suffix *context) *context {
|
|
var n int32
|
|
if a.heap2Lo < a.heap2Hi {
|
|
// allocate from top of heap2
|
|
a.heap2Hi -= 2
|
|
n = a.heap2Hi
|
|
} else if n = a.removeFreeBlock(1); n == 0 {
|
|
if n = a.allocUnitsRare(1); n == 0 {
|
|
return nil
|
|
}
|
|
}
|
|
c := &context{i: n, s: a.states[n : n+2 : n+2], a: a}
|
|
c.s[0] = state{}
|
|
c.setNumStates(1)
|
|
c.s[1] = s
|
|
if suffix != nil {
|
|
c.setSuffix(suffix)
|
|
}
|
|
return c
|
|
}
|
|
|
|
func (a *subAllocator) newContextSize(ns int) *context {
|
|
c := a.newContext(state{}, nil)
|
|
c.setNumStates(ns)
|
|
i := units2Index[(ns+1)>>1]
|
|
n := a.allocUnits(i)
|
|
c.setStatesIndex(n)
|
|
return c
|
|
}
|
|
|
|
type model struct {
|
|
maxOrder int
|
|
orderFall int
|
|
initRL int
|
|
runLength int
|
|
prevSuccess byte
|
|
escCount byte
|
|
prevSym byte
|
|
initEsc byte
|
|
minC *context
|
|
maxC *context
|
|
rc rangeCoder
|
|
a subAllocator
|
|
charMask [256]byte
|
|
binSumm [128][64]uint16
|
|
see2Cont [25][16]see2Context
|
|
}
|
|
|
|
func (m *model) restart() {
|
|
for i := range m.charMask {
|
|
m.charMask[i] = 0
|
|
}
|
|
m.escCount = 1
|
|
|
|
if m.maxOrder < 12 {
|
|
m.initRL = -m.maxOrder - 1
|
|
} else {
|
|
m.initRL = -12 - 1
|
|
}
|
|
m.orderFall = m.maxOrder
|
|
m.runLength = m.initRL
|
|
m.prevSuccess = 0
|
|
|
|
m.a.restart()
|
|
|
|
c := m.a.newContextSize(256)
|
|
c.setSummFreq(257)
|
|
states := c.states()
|
|
for i := range states {
|
|
states[i] = state{sym: byte(i), freq: 1}
|
|
}
|
|
m.minC = c
|
|
m.maxC = c
|
|
m.prevSym = 0
|
|
|
|
for i := range m.binSumm {
|
|
for j, esc := range initBinEsc {
|
|
n := binScale - esc/(uint16(i)+2)
|
|
for k := j; k < len(m.binSumm[i]); k += len(initBinEsc) {
|
|
m.binSumm[i][k] = n
|
|
}
|
|
}
|
|
}
|
|
|
|
for i := range m.see2Cont {
|
|
see := newSee2Context(5*uint16(i) + 10)
|
|
for j := range m.see2Cont[i] {
|
|
m.see2Cont[i][j] = see
|
|
}
|
|
}
|
|
}
|
|
|
|
func (m *model) init(br io.ByteReader, reset bool, maxOrder, maxMB int) error {
|
|
err := m.rc.init(br)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if !reset {
|
|
if m.minC == nil {
|
|
return errCorruptPPM
|
|
}
|
|
return nil
|
|
}
|
|
|
|
m.a.init(maxMB)
|
|
|
|
if maxOrder == 1 {
|
|
return errCorruptPPM
|
|
}
|
|
m.maxOrder = maxOrder
|
|
m.restart()
|
|
return nil
|
|
}
|
|
|
|
func (m *model) rescale(s *state) *state {
|
|
if s.freq <= maxFreq {
|
|
return s
|
|
}
|
|
c := m.minC
|
|
|
|
var summFreq uint16
|
|
|
|
s.freq += 4
|
|
states := c.states()
|
|
escFreq := c.summFreq() + 4
|
|
|
|
for i := range states {
|
|
f := states[i].freq
|
|
escFreq -= uint16(f)
|
|
if m.orderFall != 0 {
|
|
f++
|
|
}
|
|
f >>= 1
|
|
summFreq += uint16(f)
|
|
states[i].freq = f
|
|
|
|
if i == 0 || f <= states[i-1].freq {
|
|
continue
|
|
}
|
|
j := i - 1
|
|
for j > 0 && f > states[j-1].freq {
|
|
j--
|
|
}
|
|
t := states[i]
|
|
copy(states[j+1:i+1], states[j:i])
|
|
states[j] = t
|
|
}
|
|
|
|
i := len(states) - 1
|
|
for states[i].freq == 0 {
|
|
i--
|
|
escFreq++
|
|
}
|
|
if i != len(states)-1 {
|
|
states = c.shrinkStates(states, i+1)
|
|
}
|
|
s = &states[0]
|
|
if i == 0 {
|
|
for {
|
|
s.freq -= s.freq >> 1
|
|
escFreq >>= 1
|
|
if escFreq <= 1 {
|
|
return s
|
|
}
|
|
}
|
|
}
|
|
summFreq += escFreq - (escFreq >> 1)
|
|
c.setSummFreq(summFreq)
|
|
return s
|
|
}
|
|
|
|
func (m *model) decodeBinSymbol() (*state, error) {
|
|
c := m.minC
|
|
s := &c.states()[0]
|
|
|
|
ns := c.suffix().numStates()
|
|
i := m.prevSuccess + ns2BSIndex[ns-1] + byte(m.runLength>>26)&0x20
|
|
if m.prevSym >= 64 {
|
|
i += 8
|
|
}
|
|
if s.sym >= 64 {
|
|
i += 2 * 8
|
|
}
|
|
bs := &m.binSumm[s.freq-1][i]
|
|
mean := (*bs + 1<<(periodBits-2)) >> periodBits
|
|
|
|
if m.rc.currentCount(binScale) < uint32(*bs) {
|
|
err := m.rc.decode(0, uint32(*bs))
|
|
if s.freq < 128 {
|
|
s.freq++
|
|
}
|
|
*bs += 1<<intBits - mean
|
|
m.prevSuccess = 1
|
|
m.runLength++
|
|
return s, err
|
|
}
|
|
err := m.rc.decode(uint32(*bs), binScale)
|
|
*bs -= mean
|
|
m.initEsc = expEscape[*bs>>10]
|
|
m.charMask[s.sym] = m.escCount
|
|
m.prevSuccess = 0
|
|
return nil, err
|
|
}
|
|
|
|
func (m *model) decodeSymbol1() (*state, error) {
|
|
c := m.minC
|
|
states := c.states()
|
|
scale := uint32(c.summFreq())
|
|
// protect against divide by zero
|
|
// TODO: look at why this happens, may be problem elsewhere
|
|
if scale == 0 {
|
|
return nil, errCorruptPPM
|
|
}
|
|
count := m.rc.currentCount(scale)
|
|
m.prevSuccess = 0
|
|
|
|
var n uint32
|
|
for i := range states {
|
|
s := &states[i]
|
|
n += uint32(s.freq)
|
|
if n <= count {
|
|
continue
|
|
}
|
|
err := m.rc.decode(n-uint32(s.freq), n)
|
|
s.freq += 4
|
|
c.setSummFreq(uint16(scale + 4))
|
|
if i == 0 {
|
|
if 2*n > scale {
|
|
m.prevSuccess = 1
|
|
m.runLength++
|
|
}
|
|
} else {
|
|
if s.freq <= states[i-1].freq {
|
|
return s, err
|
|
}
|
|
states[i-1], states[i] = states[i], states[i-1]
|
|
s = &states[i-1]
|
|
}
|
|
return m.rescale(s), err
|
|
}
|
|
|
|
for _, s := range states {
|
|
m.charMask[s.sym] = m.escCount
|
|
}
|
|
return nil, m.rc.decode(n, scale)
|
|
}
|
|
|
|
func (m *model) makeEscFreq(c *context, numMasked int) *see2Context {
|
|
ns := c.numStates()
|
|
if ns == 256 {
|
|
return nil
|
|
}
|
|
diff := ns - numMasked
|
|
|
|
var i int
|
|
if m.prevSym >= 64 {
|
|
i = 8
|
|
}
|
|
if diff < c.suffix().numStates()-ns {
|
|
i++
|
|
}
|
|
if int(c.summFreq()) < 11*ns {
|
|
i += 2
|
|
}
|
|
if numMasked > diff {
|
|
i += 4
|
|
}
|
|
return &m.see2Cont[ns2Index[diff-1]][i]
|
|
}
|
|
|
|
func (m *model) decodeSymbol2(numMasked int) (*state, error) {
|
|
c := m.minC
|
|
|
|
see := m.makeEscFreq(c, numMasked)
|
|
scale := see.mean()
|
|
|
|
var i int
|
|
var hi uint32
|
|
states := c.states()
|
|
sl := make([]*state, len(states)-numMasked)
|
|
for j := range sl {
|
|
for m.charMask[states[i].sym] == m.escCount {
|
|
i++
|
|
}
|
|
hi += uint32(states[i].freq)
|
|
sl[j] = &states[i]
|
|
i++
|
|
}
|
|
|
|
scale += hi
|
|
count := m.rc.currentCount(scale)
|
|
|
|
if count >= scale {
|
|
return nil, errCorruptPPM
|
|
}
|
|
if count >= hi {
|
|
err := m.rc.decode(hi, scale)
|
|
if see != nil {
|
|
see.summ += uint16(scale)
|
|
}
|
|
for _, s := range sl {
|
|
m.charMask[s.sym] = m.escCount
|
|
}
|
|
return nil, err
|
|
}
|
|
|
|
hi = uint32(sl[0].freq)
|
|
for hi <= count {
|
|
sl = sl[1:]
|
|
hi += uint32(sl[0].freq)
|
|
}
|
|
s := sl[0]
|
|
|
|
err := m.rc.decode(hi-uint32(s.freq), hi)
|
|
|
|
see.update()
|
|
|
|
m.escCount++
|
|
m.runLength = m.initRL
|
|
|
|
s.freq += 4
|
|
c.setSummFreq(c.summFreq() + 4)
|
|
return m.rescale(s), err
|
|
}
|
|
|
|
func (c *context) findState(sym byte) *state {
|
|
var i int
|
|
states := c.states()
|
|
for i = range states {
|
|
if states[i].sym == sym {
|
|
break
|
|
}
|
|
}
|
|
return &states[i]
|
|
}
|
|
|
|
func (m *model) createSuccessors(s, ss *state) *context {
|
|
var sl []*state
|
|
|
|
if m.orderFall != 0 {
|
|
sl = append(sl, s)
|
|
}
|
|
|
|
c := m.minC
|
|
for suff := c.suffix(); suff != nil; suff = c.suffix() {
|
|
c = suff
|
|
|
|
if ss == nil {
|
|
ss = c.findState(s.sym)
|
|
}
|
|
if ss.succ != s.succ {
|
|
c = m.a.succContext(ss.succ)
|
|
break
|
|
}
|
|
sl = append(sl, ss)
|
|
ss = nil
|
|
}
|
|
|
|
if len(sl) == 0 {
|
|
return c
|
|
}
|
|
|
|
var up state
|
|
up.sym = m.a.succByte(s.succ)
|
|
up.succ = m.a.nextByteAddr(s.succ)
|
|
|
|
states := c.states()
|
|
if len(states) > 1 {
|
|
s = c.findState(up.sym)
|
|
|
|
cf := uint16(s.freq) - 1
|
|
s0 := c.summFreq() - uint16(len(states)) - cf
|
|
|
|
if 2*cf <= s0 {
|
|
if 5*cf > s0 {
|
|
up.freq = 2
|
|
} else {
|
|
up.freq = 1
|
|
}
|
|
} else {
|
|
up.freq = byte(1 + (2*cf+3*s0-1)/(2*s0))
|
|
}
|
|
} else {
|
|
up.freq = states[0].freq
|
|
}
|
|
|
|
for i := len(sl) - 1; i >= 0; i-- {
|
|
c = m.a.newContext(up, c)
|
|
if c == nil {
|
|
return nil
|
|
}
|
|
sl[i].succ = c.succPtr()
|
|
}
|
|
return c
|
|
}
|
|
|
|
func (m *model) update(s *state) {
|
|
if m.orderFall == 0 {
|
|
if c := m.a.succContext(s.succ); c != nil {
|
|
m.minC = c
|
|
m.maxC = c
|
|
return
|
|
}
|
|
}
|
|
|
|
if m.escCount == 0 {
|
|
m.escCount = 1
|
|
for i := range m.charMask {
|
|
m.charMask[i] = 0
|
|
}
|
|
}
|
|
|
|
var ss *state // matching minC.suffix state
|
|
|
|
if s.freq < maxFreq/4 && m.minC.suffix() != nil {
|
|
c := m.minC.suffix()
|
|
states := c.states()
|
|
|
|
var i int
|
|
if len(states) > 1 {
|
|
for states[i].sym != s.sym {
|
|
i++
|
|
}
|
|
if i > 0 && states[i].freq >= states[i-1].freq {
|
|
states[i-1], states[i] = states[i], states[i-1]
|
|
i--
|
|
}
|
|
if states[i].freq < maxFreq-9 {
|
|
states[i].freq += 2
|
|
c.setSummFreq(c.summFreq() + 2)
|
|
}
|
|
} else if states[0].freq < 32 {
|
|
states[0].freq++
|
|
}
|
|
ss = &states[i] // save later for createSuccessors
|
|
}
|
|
|
|
if m.orderFall == 0 {
|
|
c := m.createSuccessors(s, ss)
|
|
if c == nil {
|
|
m.restart()
|
|
} else {
|
|
m.minC = c
|
|
m.maxC = c
|
|
s.succ = c.succPtr()
|
|
}
|
|
return
|
|
}
|
|
|
|
succ := m.a.pushByte(s.sym)
|
|
if m.a.succIsNil(succ) {
|
|
m.restart()
|
|
return
|
|
}
|
|
|
|
var minC *context
|
|
if m.a.succIsNil(s.succ) {
|
|
s.succ = succ
|
|
minC = m.minC
|
|
} else {
|
|
minC = m.a.succContext(s.succ)
|
|
if minC == nil {
|
|
minC = m.createSuccessors(s, ss)
|
|
if minC == nil {
|
|
m.restart()
|
|
return
|
|
}
|
|
}
|
|
m.orderFall--
|
|
if m.orderFall == 0 {
|
|
succ = minC.succPtr()
|
|
if m.maxC.notEq(m.minC) {
|
|
m.a.popByte()
|
|
}
|
|
}
|
|
}
|
|
|
|
n := m.minC.numStates()
|
|
s0 := int(m.minC.summFreq()) - n - int(s.freq-1)
|
|
for c := m.maxC; c.notEq(m.minC); c = c.suffix() {
|
|
var summFreq uint16
|
|
|
|
states := c.expandStates()
|
|
if states == nil {
|
|
m.restart()
|
|
return
|
|
}
|
|
if ns := len(states) - 1; ns != 1 {
|
|
summFreq = c.summFreq()
|
|
if 4*ns <= n && int(summFreq) <= 8*ns {
|
|
summFreq += 2
|
|
}
|
|
if 2*ns < n {
|
|
summFreq++
|
|
}
|
|
} else {
|
|
p := &states[0]
|
|
if p.freq < maxFreq/4-1 {
|
|
p.freq += p.freq
|
|
} else {
|
|
p.freq = maxFreq - 4
|
|
}
|
|
summFreq = uint16(p.freq) + uint16(m.initEsc)
|
|
if n > 3 {
|
|
summFreq++
|
|
}
|
|
}
|
|
|
|
cf := 2 * int(s.freq) * int(summFreq+6)
|
|
sf := s0 + int(summFreq)
|
|
var freq byte
|
|
if cf >= 6*sf {
|
|
switch {
|
|
case cf >= 15*sf:
|
|
freq = 7
|
|
case cf >= 12*sf:
|
|
freq = 6
|
|
case cf >= 9*sf:
|
|
freq = 5
|
|
default:
|
|
freq = 4
|
|
}
|
|
summFreq += uint16(freq)
|
|
} else {
|
|
switch {
|
|
case cf >= 4*sf:
|
|
freq = 3
|
|
case cf > sf:
|
|
freq = 2
|
|
default:
|
|
freq = 1
|
|
}
|
|
summFreq += 3
|
|
}
|
|
states[len(states)-1] = state{sym: s.sym, freq: freq, succ: succ}
|
|
c.setSummFreq(summFreq)
|
|
}
|
|
m.minC = minC
|
|
m.maxC = minC
|
|
}
|
|
|
|
func (m *model) ReadByte() (byte, error) {
|
|
if m.minC == nil {
|
|
return 0, errCorruptPPM
|
|
}
|
|
var s *state
|
|
var err error
|
|
if m.minC.numStates() == 1 {
|
|
s, err = m.decodeBinSymbol()
|
|
} else {
|
|
s, err = m.decodeSymbol1()
|
|
}
|
|
for s == nil && err == nil {
|
|
n := m.minC.numStates()
|
|
for m.minC.numStates() == n {
|
|
m.orderFall++
|
|
m.minC = m.minC.suffix()
|
|
if m.minC == nil {
|
|
return 0, errCorruptPPM
|
|
}
|
|
}
|
|
s, err = m.decodeSymbol2(n)
|
|
}
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
|
|
// save sym so it doesn't get overwritten by a possible restart()
|
|
sym := s.sym
|
|
m.update(s)
|
|
m.prevSym = sym
|
|
return sym, nil
|
|
}
|