Function buildDtableRef

zstd/fse_decoder_arm64_test.go:16–71

buildDtableRef is a copy of the pure-Go reference algorithm (fse_decoder_generic.go), kept here so the arm64 asm implementation can be differentially tested against it even though the generic file is not compiled on arm64.

(s *fseDecoder)

// differentially tested against it even though the generic file is not
// compiled on arm64.
func buildDtableRef(s *fseDecoder) error {
	tableSize := uint32(1 << s.actualTableLog)
	highThreshold := tableSize - 1
	symbolNext := s.stateTable[:256]

	{
		for i, v := range s.norm[:s.symbolLen] {
			if v == -1 {
				s.dt[highThreshold].setAddBits(uint8(i))
				highThreshold--
				v = 1
			}
			symbolNext[i] = uint16(v)
		}
	}

	{
		tableMask := tableSize - 1
		step := tableStep(tableSize)
		position := uint32(0)
		for ss, v := range s.norm[:s.symbolLen] {
			for i := 0; i < int(v); i++ {
				s.dt[position].setAddBits(uint8(ss))
				for {
					position = (position + step) & tableMask
					if position <= highThreshold {
						break
					}
				}
			}
		}
		if position != 0 {
			return errors.New("corrupted input (position != 0)")
		}
	}

	{
		tableSize := uint16(1 << s.actualTableLog)
		for u, v := range s.dt[:tableSize] {
			symbol := v.addBits()
			nextState := symbolNext[symbol]
			symbolNext[symbol] = nextState + 1
			nBits := s.actualTableLog - byte(highBits(uint32(nextState)))
			s.dt[u&maxTableMask].setNBits(nBits)
			newState := (nextState << nBits) - tableSize
			if newState > tableSize {
				return fmt.Errorf("newState (%d) outside table size (%d)", newState, tableSize)
			}
			if newState == uint16(u) && nBits == 0 {
				return fmt.Errorf("newState (%d) == oldState (%d) and no bits", newState, u)
			}
			s.dt[u&maxTableMask].setNewState(newState)
		}
	}
	return nil
}

func TestBuildDtableARM64MatchesReference(t *testing.T) {