mpeg2_vld_intra_n.h

h263,jpeg,mpeg2编解码核心程序(TI DSP C64xx)

/*      2. bptr: bptr is the bit pointer which points to the current        */
/*      bit WITHIN the word pointed to by next_wptr.                        */
/*                                                                          */
/*          bptr = bsptr & 31;                                              */
/*          bptr_cmpl = 32 - bptr;                                          */
/*                                                                          */
/*      3. word1 and word2: read next 3 words from the bitstream buffer     */
/*      (word0 is a temporary variable). bsbuf_words is the size of the     */
/*      bitstream buffer in words.                                          */
/*                                                                          */
/*          word0 = bsbuf[next_wptr];                                       */
/*          next_wptr = (next_wptr + 1) & (bsbuf_words-1);                  */
/*                                                                          */
/*          word1 = bsbuf[next_wptr];                                       */
/*          next_wptr = (next_wptr + 1) & (bsbuf_words-1);                  */
/*                                                                          */
/*          word2 = bsbuf[next_wptr];                                       */
/*          next_wptr = (next_wptr + 1) & (bsbuf_words-1);                  */
/*                                                                          */
/*      4. top0 and top1: Shift words word0, word1, word2 by bptr to the    */
/*      left so that the current bit becomes the MSB in word0. word0 can    */
/*      simply be shifted by bptr; the then empty LSBs of word0 have to be  */
/*      filled with the MSBs of word1. To do that the required MSBs are     */
/*      brought into the position of empty LSBs of word0 by shifting word1  */
/*      to the right by (32-bptr). The result is then copied into word0 by  */
/*      an addition. Rather than overwriting word0, top0 is used to hold    */
/*      the new bit aligned word. The same procedure is used to obtain      */
/*      top1. top0 and top1 contain the next 64 bits of the bitstream.      */
/*                                                                          */
/*          s1 = word0 << bptr;                                             */
/*          s2 = word1 >> bptr_cmpl;  // unsigned right-shift //            */
/*          top0 = s1 + s2;                                                 */
/*                                                                          */
/*          s3 = word1 << bptr;                                             */
/*          s4 = word2 >> bptr_cmpl;  // unsigned right-shift //            */
/*          top1 = s3 + s4;                                                 */
/*                                                                          */
/*      Note that the routine returns the updated state of the bitstream    */
/*      buffer variables, top0, top1, word1, word2, bptr and next_wptr. If  */
/*      all other functions which access the bitstream in a decoder system  */
/*      maintain the buffer variables in the same way, then the above       */
/*      initialization procedure has to be performed only once at the       */
/*      beginning.                                                          */
/*                                                                          */
/*  TECHNIQUES                                                              */
/*      The instruction NORM is used to detect the number of leading zeros  */
/*      or ones in a code word. This value together with additional bits    */
/*      extracted from the codeword is then used as an index into look-up   */
/*      tables to determine the length, run, level and sign. Escape code    */
/*      sequences are directly extracted from the code word.                */
/*                                                                          */
/*      DC coefficients are decoded without lookup tables by exploiting     */
/*      the relatively simple relationship between the number of leading    */
/*      zeros and dc_size and the length of the code word.                  */
/*                                                                          */
/*  ASSUMPTIONS                                                             */
/*      The bitstream must be stored in memory in 32-bit words which are    */
/*      in little endian byte order.                                        */
/*                                                                          */
/*      Wptr is allowed to overrun once (to detect total run overrun), so   */
/*      maximum overrun that can occur is 66 (Error mark). Therefore,       */
/*      in memory 66+1 halfwords behind the weighting matrix should be      */
/*      valid (e.g. peripherals). No memory is overwritten,                 */
/*      only loads occurr.                                                  */
/*                                                                          */
/*      Note that the AMR register is set to zero on exit.                  */
/*                                                                          */
/*  DATA SIZE                                                               */
/*      3584 bytes for the lookup tables                                    */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2002 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */
#ifndef MPEG2_VLD_INTRA_N_H_
#define MPEG2_VLD_INTRA_N_H_ 1

#ifndef IMG_MPEG2_VLD_STRUCT_
#define IMG_MPEG2_VLD_STRUCT_ 1

typedef struct {
    unsigned int  *bsbuf;      // pointer to bitstream buffer
    unsigned int  next_wptr;   // next word to read from buffer
    unsigned int  bptr;        // bit position within word
    unsigned int  word1;       // word aligned buffer
    unsigned int  word2;       // word aligned buffer
    unsigned int  top0;        // top 32 bits of bitstream
    unsigned int  top1;        // next 32 bits of bitstream
    const unsigned char *scan; // inverse zigzag scan matrix
    unsigned int  intravlc;    // intra_vlc_format
    unsigned int  quant_scale; // quant_scale
    unsigned int  dc_prec;     // intra_dc_precision
    unsigned int  cbp;         // coded_block_pattern
    unsigned int  fault;       // fault condition (returned)
    unsigned int  reserved;    // reserved
} IMG_mpeg2_vld;

#endif

void mpeg2_vld_intra_nsa
(
    const short    *restrict Wptr,
    short          *restrict outi,
    IMG_mpeg2_vld  *restrict Mpeg2v,
    int            dc_pred[3],
    int            mode_12Q4,
    int            num_blocks,
    int            bsbuf_words
);

#endif
/* ======================================================================== */
/*  End of file:  mpeg2_vld_intra_n.h                                       */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2002 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */