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Code Issues Releases Activity

switch ac3enc to av_crc

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Originally committed as revision 5116 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2006-03-06 14:53:13 +00:00
parent 43a80ccee5
commit e027d0a81e
3 changed files with 5 additions and 34 deletions
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35
libavcodec/ac3enc.c
View File

@ -25,6 +25,7 @@
//#define DEBUG_BITALLOC
#include "avcodec.h"
#include "bitstream.h"
#include "crc.h"
#include "ac3.h"
typedef struct AC3EncodeContext {
@ -66,7 +67,6 @@ typedef struct AC3EncodeContext {
#define EXP_DIFF_THRESHOLD 1000
static void fft_init(int ln);
static void ac3_crc_init(void);
static inline int16_t fix15(float a)
{
@ -886,8 +886,6 @@ static int AC3_encode_init(AVCodecContext *avctx)
xsin1[i] = fix15(-sin(alpha));
}
ac3_crc_init();
avctx->coded_frame= avcodec_alloc_frame();
avctx->coded_frame->key_frame= 1;
@ -1236,35 +1234,8 @@ static void output_audio_block(AC3EncodeContext *s,
}
}
/* compute the ac3 crc */
#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
static void ac3_crc_init(void)
{
unsigned int c, n, k;
for(n=0;n<256;n++) {
c = n << 8;
for (k = 0; k < 8; k++) {
if (c & (1 << 15))
c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);
else
c = c << 1;
}
crc_table[n] = c;
}
}
static unsigned int ac3_crc(uint8_t *data, int n, unsigned int crc)
{
int i;
for(i=0;i<n;i++) {
crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;
}
return crc;
}
static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
{
unsigned int c;
@ -1342,14 +1313,14 @@ static int output_frame_end(AC3EncodeContext *s)
/* Now we must compute both crcs : this is not so easy for crc1
because it is at the beginning of the data... */
frame_size_58 = (frame_size >> 1) + (frame_size >> 3);
crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);
crc1 = bswap_16(av_crc(av_crc8005, 0, frame + 4, 2 * frame_size_58 - 4));
/* XXX: could precompute crc_inv */
crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);
crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
frame[2] = crc1 >> 8;
frame[3] = crc1;
crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);
crc2 = bswap_16(av_crc(av_crc8005, 0, frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2));
frame[2*frame_size - 2] = crc2 >> 8;
frame[2*frame_size - 1] = crc2;

2
libavcodec/ac3tab.h
View File

@ -182,5 +182,3 @@ static int16_t sintab[64];
static int16_t fft_rev[512];
static int16_t xcos1[128];
static int16_t xsin1[128];
static uint16_t crc_table[256];

2
libavcodec/utils.c
View File

@ -1221,7 +1221,9 @@ unsigned avcodec_build( void )
static void init_crcs(void){
av_crc04C11DB7= av_mallocz_static(sizeof(AVCRC) * 257);
av_crc8005 = av_mallocz_static(sizeof(AVCRC) * 257);
av_crc_init(av_crc04C11DB7, 0, 32, 0x04c11db7, sizeof(AVCRC)*257);
av_crc_init(av_crc8005 , 0, 16, 0x8005 , sizeof(AVCRC)*257);
}
/* must be called before any other functions */