Entropy coding primary and secondary coefficients of video data

An apparatus for determining numbers of bits to use to encode quantized transform coefficients of a transform block, the apparatus comprising:

• a processor configured to execute instructions stored in a non-transitory storage medium to:
• store, within a hardware register, sets of context data corresponding to categories of a probability model available for encoding the quantized transform coefficients;
• identify one of the quantized transform coefficients as a primary coefficient;
• identify at least one valid secondary coefficient associated with the primary coefficient, the at least one valid secondary coefficient located before a last non-zero coefficient within the transform block;
• identify one of the categories of the probability model as a category used to encode one or more neighbor coefficients of the primary coefficient and one or more neighbor coefficients of the at least one valid secondary coefficient;
• access, in a single clock cycle, the hardware register to retrieve one of the sets of context data associated with the identified category;
• determine a number of bits to use to encode each of the primary coefficient and the at least one valid secondary coefficient based on the retrieved set of context data accessed in the single clock cycle;
• and
• encode, to a bitstream, the primary coefficient and the at least one valid secondary coefficient using the number of bits.

A method for determining numbers of bits to use to encode quantized transform coefficients of a transform block, the method comprising:

• storing, within a hardware register, sets of context data corresponding to categories of a probability model available for encoding the quantized transform coefficients;
• identifying one of the quantized transform coefficients as a primary coefficient;
• identifying a quantized transform coefficient immediately following the primary coefficient within the transform block as a secondary coefficient;
• determining that the secondary coefficient is valid based on a value of the primary coefficient, a value of the secondary coefficient, and a location of a last non-zero quantized coefficient within the transform block;
• identifying one of the categories of the probability model as a category used to encode one or more neighbor coefficients of one or more of the primary coefficient or the valid secondary coefficient;
• determining a context to use to encode the primary coefficient and the valid secondary coefficient based on the identified category;
• accessing, in a single clock cycle, the hardware register to retrieve one of the sets of context data associated with the context to use to encode the primary coefficient and the valid secondary coefficient;
• determining a number of bits to use to encode the primary coefficient and the valid secondary coefficient based on the retrieved set of context data accessed in the single clock cycle;
• and
• encoding, to a bitstream, the primary coefficient and the valid secondary coefficient using the number of bits.