Algorithm 6 Variable bit-length ADPCM decoder.

Require:p // ADPCM value. Require: M // bits of the current ADPCM value. Require: $InitW$ // if the predicted offset is initialized or not. Require: $W_{init}$ // a predicted offset to be initialized. Require: $InitP$ // if the $P_{prev}$ is initialized or not. Require: $P_{init}$ // an original data to be set to $P_{prev}$. Ensure: P // N bit Pixel element.  if $M=N$ then    $P\leftarrow p$   return  end if  if $M\ne M_{prev}$ then   if $M>M_{prev}$ then     $w\leftarrow w\ll (M-M_{prev})$   else     $w\leftarrow w\gg (M_{prev}-M)$   end if  end if  if $InitW=true$ then    $w\leftarrow W_{init}$  end if  if $InitP=true$ then    $P_{prev}\leftarrow P_{init}$  end if   $step\leftarrow (w\times 2)/2^{M-1}$  if $p<2^{M-1}$ then    $d\leftarrow step\times (p\times 2+1)/2$  else    $d\leftarrow -step\times ((p-2^{M-1})\times 2+1)/2$  end if   $P\leftarrow P_{prev}+d$   $f_{prev}\leftarrow f_{prev}\times C[p\&((1\ll M)-1)]/64$   $w\leftarrow f_{prev}$