buildDtable will build the decoding table.
()
| 9 | |
| 10 | // buildDtable will build the decoding table. |
| 11 | func (s *fseDecoder) buildDtable() error { |
| 12 | tableSize := uint32(1 << s.actualTableLog) |
| 13 | highThreshold := tableSize - 1 |
| 14 | symbolNext := s.stateTable[:256] |
| 15 | |
| 16 | // Init, lay down lowprob symbols |
| 17 | { |
| 18 | for i, v := range s.norm[:s.symbolLen] { |
| 19 | if v == -1 { |
| 20 | s.dt[highThreshold].setAddBits(uint8(i)) |
| 21 | highThreshold-- |
| 22 | v = 1 |
| 23 | } |
| 24 | symbolNext[i] = uint16(v) |
| 25 | } |
| 26 | } |
| 27 | |
| 28 | // Spread symbols |
| 29 | { |
| 30 | tableMask := tableSize - 1 |
| 31 | step := tableStep(tableSize) |
| 32 | position := uint32(0) |
| 33 | for ss, v := range s.norm[:s.symbolLen] { |
| 34 | for i := 0; i < int(v); i++ { |
| 35 | s.dt[position].setAddBits(uint8(ss)) |
| 36 | for { |
| 37 | // lowprob area |
| 38 | position = (position + step) & tableMask |
| 39 | if position <= highThreshold { |
| 40 | break |
| 41 | } |
| 42 | } |
| 43 | } |
| 44 | } |
| 45 | if position != 0 { |
| 46 | // position must reach all cells once, otherwise normalizedCounter is incorrect |
| 47 | return errors.New("corrupted input (position != 0)") |
| 48 | } |
| 49 | } |
| 50 | |
| 51 | // Build Decoding table |
| 52 | { |
| 53 | tableSize := uint16(1 << s.actualTableLog) |
| 54 | for u, v := range s.dt[:tableSize] { |
| 55 | symbol := v.addBits() |
| 56 | nextState := symbolNext[symbol] |
| 57 | symbolNext[symbol] = nextState + 1 |
| 58 | nBits := s.actualTableLog - byte(highBits(uint32(nextState))) |
| 59 | s.dt[u&maxTableMask].setNBits(nBits) |
| 60 | newState := (nextState << nBits) - tableSize |
| 61 | if newState > tableSize { |
| 62 | return fmt.Errorf("newState (%d) outside table size (%d)", newState, tableSize) |
| 63 | } |
| 64 | if newState == uint16(u) && nBits == 0 { |
| 65 | // Seems weird that this is possible with nbits > 0. |
| 66 | return fmt.Errorf("newState (%d) == oldState (%d) and no bits", newState, u) |
| 67 | } |
| 68 | s.dt[u&maxTableMask].setNewState(newState) |
nothing calls this directly
no test coverage detected