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apv_decode: Multisymbol entropy decode

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This commit is contained in:
Mark Thompson
2025-05-05 21:04:54 +01:00
parent 9980a0b9b1
commit a3c8fba5da
3 changed files with 536 additions and 130 deletions
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59
libavcodec/apv_decode.h
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@ -33,14 +33,39 @@
#define APV_VLC_LUT_BITS 9
#define APV_VLC_LUT_SIZE (1 << APV_VLC_LUT_BITS)
typedef struct APVVLCLUTEntry {
typedef struct APVSingleVLCLUTEntry {
uint16_t result; // Return value if not reading more.
uint8_t consume; // Number of bits to consume.
uint8_t more; // Whether to read additional bits.
} APVVLCLUTEntry;
} APVSingleVLCLUTEntry;
typedef struct APVMultiVLCLUTEntry {
// Number of symbols this bit stream resolves to.
uint8_t count;
// k_run after decoding all symbols.
uint8_t k_run : 2;
// k_level after decoding the first level symbol.
uint8_t k_level_0 : 3;
// k_level after decoding all symbols.
uint8_t k_level_1 : 3;
// Run output values.
uint8_t run[2];
// Level output values.
int16_t level[2];
// Bit index of the end of each code.
uint8_t offset[4];
} APVMultiVLCLUTEntry;
typedef struct APVVLCLUT {
APVVLCLUTEntry lut[6][APV_VLC_LUT_SIZE];
// Single-symbol LUT for VLCs.
// Applies to all coefficients, but used only for DC coefficients
// in the decoder.
APVSingleVLCLUTEntry single_lut[6][APV_VLC_LUT_SIZE];
// Multi-symbol LUT for run/level combinations, decoding up to four
// symbols per step. Comes in two versions, which to use depends on
// whether the next symbol is a run or a level.
APVMultiVLCLUTEntry run_first_lut[3][5][APV_VLC_LUT_SIZE];
APVMultiVLCLUTEntry level_first_lut[3][5][APV_VLC_LUT_SIZE];
} APVVLCLUT;
typedef struct APVEntropyState {
@ -48,33 +73,29 @@ typedef struct APVEntropyState {
const APVVLCLUT *decode_lut;
// Previous DC level value.
int16_t prev_dc;
int16_t prev_dc_diff;
int16_t prev_1st_ac_level;
// k parameter implied by the previous DC level value.
uint8_t prev_k_dc;
// k parameter implied by the previous first AC level value.
uint8_t prev_k_level;
} APVEntropyState;
/**
* Build the decoder VLC look-up table.
* Build the decoder VLC look-up tables.
*/
void ff_apv_entropy_build_decode_lut(APVVLCLUT *decode_lut);
/**
* Entropy decode a single 8x8 block to coefficients.
*
* Outputs in block order (dezigzag already applied).
* Outputs nonzero coefficients only to the block row-major order
* (dezigzag is applied within the function). The output block
* must have been filled with zeroes before calling this function.
*/
int ff_apv_entropy_decode_block(int16_t *coeff,
GetBitContext *gbc,
APVEntropyState *state);
/**
* Read a single APV VLC code.
*
* This entrypoint is exposed for testing.
*/
unsigned int ff_apv_read_vlc(GetBitContext *gbc, int k_param,
const APVVLCLUT *lut);
int ff_apv_entropy_decode_block(int16_t *restrict coeff,
GetBitContext *restrict gbc,
APVEntropyState *restrict state);
#endif /* AVCODEC_APV_DECODE_H */