Class RANSDecodingSymbol

java.lang.Object
htsjdk.samtools.cram.compression.rans.RANSDecodingSymbol
public final class RANSDecodingSymbol extends Object
Holds the start and frequency for a single symbol in the rANS decoding table. The reverse-lookup table mapping cumulative frequency to symbol is held separately in the decoder's reverseLookup arrays.

Decoding a symbol is a two-step process:

  1. advanceSymbolStep(long, int) — updates the rANS state using the symbol's range
  2. Utils.RANSDecodeRenormalizeNx16(long, byte[], int[]) or Utils.RANSDecodeRenormalize4x8(long, byte[], int[]) — renormalizes by reading bytes from the compressed stream

  • Constructor Details

    • RANSDecodingSymbol

      public RANSDecodingSymbol()

  • Method Details

    • set

      public void set(int start, int freq)
      Set the decoding parameters for this symbol.
      Parameters:
      start - the cumulative frequency of all preceding symbols
      freq - the frequency of this symbol

    • advanceSymbolStep

      public long advanceSymbolStep(long r, int scaleBits)
      Advance the rANS state by one decoded symbol. Does not renormalize — the caller must call the appropriate Utils.RANSDecodeRenormalize* method after this.
      Parameters:
      r - the current rANS state
      scaleBits - the frequency scale (log2 of total frequency sum)
      Returns:
      the updated rANS state (before renormalization)