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alac: clean up and update comments leftover from reverse-engineering

This commit is contained in:
Justin Ruggles 2012-07-09 10:10:02 -04:00
parent 3bab7cd128
commit 2ac1737583
1 changed files with 18 additions and 31 deletions
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45
libavcodec/alac.c
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@ -70,19 +70,16 @@ typedef struct {
int32_t *extra_bits_buffer[MAX_CHANNELS]; int32_t *extra_bits_buffer[MAX_CHANNELS];
/* stuff from setinfo */ uint32_t setinfo_max_samples_per_frame;
uint32_t setinfo_max_samples_per_frame; /* 0x1000 = 4096 */ /* max samples per frame? */ uint8_t setinfo_sample_size;
uint8_t setinfo_sample_size; /* 0x10 */ uint8_t setinfo_rice_historymult;
uint8_t setinfo_rice_historymult; /* 0x28 */ uint8_t setinfo_rice_initialhistory;
uint8_t setinfo_rice_initialhistory; /* 0x0a */ uint8_t setinfo_rice_kmodifier;
uint8_t setinfo_rice_kmodifier; /* 0x0e */
/* end setinfo stuff */
int extra_bits; /**< number of extra bits beyond 16-bit */ int extra_bits; /**< number of extra bits beyond 16-bit */
} ALACContext; } ALACContext;
static inline int decode_scalar(GetBitContext *gb, int k, int limit, int readsamplesize){ static inline int decode_scalar(GetBitContext *gb, int k, int limit, int readsamplesize){
/* read x - number of 1s before 0 represent the rice */
int x = get_unary_0_9(gb); int x = get_unary_0_9(gb);
if (x > 8) { /* RICE THRESHOLD */ if (x > 8) { /* RICE THRESHOLD */
@ -111,12 +108,11 @@ static inline int decode_scalar(GetBitContext *gb, int k, int limit, int readsam
static void bastardized_rice_decompress(ALACContext *alac, static void bastardized_rice_decompress(ALACContext *alac,
int32_t *output_buffer, int32_t *output_buffer,
int output_size, int output_size,
int readsamplesize, /* arg_10 */ int readsamplesize,
int rice_initialhistory, /* arg424->b */ int rice_initialhistory,
int rice_kmodifier, /* arg424->d */ int rice_kmodifier,
int rice_historymult, /* arg424->c */ int rice_historymult,
int rice_kmodifier_mask /* arg424->e */ int rice_kmodifier_mask)
)
{ {
int output_count; int output_count;
unsigned int history = rice_initialhistory; unsigned int history = rice_initialhistory;
@ -203,10 +199,8 @@ static void predictor_decompress_fir_adapt(int32_t *error_buffer,
return; return;
} }
if (predictor_coef_num == 0x1f) { /* 11111 - max value of predictor_coef_num */ if (predictor_coef_num == 31) {
/* second-best case scenario for fir decompression, /* simple 1st-order prediction */
* error describes a small difference from the previous sample only
*/
if (output_size <= 1) if (output_size <= 1)
return; return;
for (i = 0; i < output_size - 1; i++) { for (i = 0; i < output_size - 1; i++) {
@ -231,9 +225,7 @@ static void predictor_decompress_fir_adapt(int32_t *error_buffer,
buffer_out[i+1] = val; buffer_out[i+1] = val;
} }
/* 4 and 8 are very common cases (the only ones i've seen). these /* NOTE: 4 and 8 are very common cases that could be optimized. */
* should be unrolled and optimized
*/
/* general case */ /* general case */
if (predictor_coef_num > 0) { if (predictor_coef_num > 0) {
@ -371,14 +363,10 @@ static int alac_decode_frame(AVCodecContext *avctx, void *data,
return AVERROR_INVALIDDATA; return AVERROR_INVALIDDATA;
} }
/* 2^result = something to do with output waiting. skip_bits(&alac->gb, 4); /* element instance tag */
* perhaps matters if we read > 1 frame in a pass? skip_bits(&alac->gb, 12); /* unused header bits */
*/
skip_bits(&alac->gb, 4);
skip_bits(&alac->gb, 12); /* unknown, skip 12 bits */ /* the number of output samples is stored in the frame */
/* the output sample size is stored soon */
hassize = get_bits1(&alac->gb); hassize = get_bits1(&alac->gb);
alac->extra_bits = get_bits(&alac->gb, 2) << 3; alac->extra_bits = get_bits(&alac->gb, 2) << 3;
@ -578,7 +566,6 @@ static int alac_set_info(ALACContext *alac)
bytestream2_skipu(&gb, 12); // size:4, alac:4, version:4 bytestream2_skipu(&gb, 12); // size:4, alac:4, version:4
/* buffer size / 2 ? */
alac->setinfo_max_samples_per_frame = bytestream2_get_be32u(&gb); alac->setinfo_max_samples_per_frame = bytestream2_get_be32u(&gb);
if (alac->setinfo_max_samples_per_frame >= UINT_MAX/4){ if (alac->setinfo_max_samples_per_frame >= UINT_MAX/4){
av_log(alac->avctx, AV_LOG_ERROR, av_log(alac->avctx, AV_LOG_ERROR,