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tree.go
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tree.go
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package lzma
type treedecoder struct {
probs []prob
}
func newTree(numBits int) *treedecoder {
tree := new(treedecoder)
tree.probs = make([]prob, numBits)
return tree
}
func (t *treedecoder) decode(rd *rangedecoder) (uint, error) {
m := uint(1)
for _, prob := range t.probs {
bit, err := rd.decodeBit(&prob)
if err != nil {
return 0, err
}
m = (m << 1) + bit
}
return m - uint(1 << uint(len(t.probs))), nil
}
func (t *treedecoder) reverseDecode(rd *rangedecoder) (uint, error) {
return reverseDecode(t.probs, rd)
}
func reverseDecode(probs []prob, rd *rangedecoder) (uint, error) {
m := uint(1)
symbol := uint(0)
for pos, prob := range probs {
bit, err := rd.decodeBit(&prob)
if err != nil {
return 0, err
}
m <<= 1
m += bit
symbol |= bit << uint(pos)
}
return symbol, nil
}