bits.cpp

传输流分析

/* putbits.c, bit-level output                                              */

/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */

/*
 * Disclaimer of Warranty
 *
 * These software programs are available to the user without any license fee or
 * royalty on an "as is" basis.  The MPEG Software Simulation Group disclaims
 * any and all warranties, whether express, implied, or statuary, including any
 * implied warranties or merchantability or of fitness for a particular
 * purpose.  In no event shall the copyright-holder be liable for any
 * incidental, punitive, or consequential damages of any kind whatsoever
 * arising from the use of these programs.
 *
 * This disclaimer of warranty extends to the user of these programs and user's
 * customers, employees, agents, transferees, successors, and assigns.
 *
 * The MPEG Software Simulation Group does not represent or warrant that the
 * programs furnished hereunder are free of infringement of any third-party
 * patents.
 *
 * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
 * are subject to royalty fees to patent holders.  Many of these patents are
 * general enough such that they are unavoidable regardless of implementation
 * design.
 *
 */

#include "main.h"

/* initialize buffer, call once before first putbits or alignbits */
int init_putbits(bitstream *bs, char *bs_filename)
{
        char tmpStr[MAXPATH];

        if ((bs->bitfile = fopen(bs_filename, "wb")) == NULL) {
                sprintf(tmpStr, "Unable to open file %s for writing: %s.",
                        bs_filename, strerrno());
                DisplayError(tmpStr);
                return FALSE;
        }
        bs->bfr = (unsigned char*)malloc(BUFFER_SIZE);
        if (!bs->bfr) {
                fclose(bs->bitfile);
                sprintf(tmpStr, "Unable to allocate memory for bitstream file %s.", bs_filename);
                DisplayError(tmpStr);
                return FALSE;
        }
        bs->bitidx = 8;
        bs->byteidx = 0;
        bs->totbits = 0.0;
        bs->outbyte = 0;
        bs->fileOutError = FALSE;
        return TRUE;
}

void finish_putbits(bitstream *bs)
{
        if (bs->bitfile) {
                if ((bs->byteidx) && (!bs->fileOutError))
                        fwrite(bs->bfr, sizeof(unsigned char), bs->byteidx, bs->bitfile);
                fclose(bs->bitfile);
                bs->bitfile = NULL;
        }
        if (bs->bfr) {
                free(bs->bfr);
                bs->bfr = NULL;
        }
}

static void putbyte(bitstream *bs)
{
        if (!bs->fileOutError) {
                bs->bfr[bs->byteidx++] = bs->outbyte;
                if (bs->byteidx == BUFFER_SIZE) {
                        if (fwrite(bs->bfr, sizeof(unsigned char), BUFFER_SIZE, bs->bitfile) != BUFFER_SIZE)
                                bs->fileOutError = TRUE;
                        bs->byteidx = 0;
                }
        }
        bs->bitidx = 8;
}

/* write rightmost n (0<=n<=32) bits of val to outfile */
void putbits(bitstream *bs, int val, int n)
{
        int i;
        unsigned int mask;

        mask = 1 << (n - 1); /* selects first (leftmost) bit */
        for (i = 0; i < n; i++) {
                bs->totbits += 1;
                bs->outbyte <<= 1;
                if (val & mask)
                        bs->outbyte |= 1;
                mask >>= 1; /* select next bit */
                bs->bitidx--;
                if (bs->bitidx == 0) /* 8 bit buffer full */
                        putbyte(bs);
        }
}

/* write rightmost bit of val to outfile */
void put1bit(bitstream *bs, int val)
{
        bs->totbits += 1;
        bs->outbyte <<= 1;
        if (val & 0x1)
                bs->outbyte |= 1;
        bs->bitidx--;
        if (bs->bitidx == 0) /* 8 bit buffer full */
                putbyte(bs);
}

/* Prepare a upcoming undo at the beginning of a GOP */
void prepareundo(bitstream *bs, bitstream *undo)
{
        memcpy(ubuffer, bs->bfr, BUFFER_SIZE);
        fgetpos(bs->bitfile, &bs->actpos);
        *undo = *bs;
}

/* Reset old status, undo all changes made up to a point */
void undochanges(bitstream *bs, bitstream *old)
{
        memcpy(bs->bfr, ubuffer, BUFFER_SIZE);
        fsetpos(bs->bitfile, &bs->actpos);
        *bs = *old;
}

/* zero bit stuffing to next byte boundary (5.2.3, 6.2.1) */
void alignbits(bitstream *bs)
{
        if (bs->bitidx != 8)
                putbits(bs, 0, bs->bitidx);
}

/* return total number of generated bits */
double bitcount(bitstream *bs)
{
        return bs->totbits;
}

static int refill_buffer(bitstream *bs)
{
        int i;

        i = fread(bs->bfr, sizeof(unsigned char), BUFFER_SIZE, bs->bitfile);
        if (!i) {
                bs->eobs = TRUE;
                return FALSE;
        }
        bs->bufcount = i;
        return TRUE;
}

/* open the device to read the bit stream from it */
int init_getbits(bitstream *bs, char *bs_filename)
{
        char tmpStr[MAXPATH];

        if ((bs->bitfile = fopen(bs_filename, "rb")) == NULL) {
                sprintf(tmpStr, "Unable to open file %s for reading: %s.",
                        bs_filename, strerrno());
                DisplayError(tmpStr);
                return FALSE;
        }
        bs->bfr = (unsigned char*)malloc(BUFFER_SIZE);
        if (!bs->bfr) {
                fclose(bs->bitfile);
                sprintf(tmpStr, "Unable to allocate memory for bitstream file %s.", bs_filename);
                DisplayError(tmpStr);
                return FALSE;
        }
        bs->byteidx = 0;
        bs->bitidx = 8;
        bs->totbits = 0.0;
        bs->bufcount = 0;
        bs->eobs = FALSE;
        if (!refill_buffer(bs)) {
                if (bs->eobs) {
                        sprintf(tmpStr, "Unable to read from file %s.", bs_filename);
                        DisplayError(tmpStr);
                        return FALSE;
                }
        }
        return TRUE;
}

/*close the device containing the bit stream after a read process*/
void finish_getbits(bitstream *bs)
{
        if (bs->bitfile)
                fclose(bs->bitfile);
        bs->bitfile = NULL;
}

int masks[8]={0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80};

/*read 1 bit from the bit stream */
int get1bit(bitstream *bs, unsigned int *retval)
{
        unsigned int bit;

        if (bs->eobs)
                return FALSE;

        bit = (bs->bfr[bs->byteidx] & masks[bs->bitidx - 1]) >> (bs->bitidx - 1);
        bs->totbits++;
        bs->bitidx--;
        if (!bs->bitidx) {
                bs->bitidx = 8;
                bs->byteidx++;
                if (bs->byteidx == bs->bufcount) {
                        if (bs->bufcount == BUFFER_SIZE)
                                refill_buffer(bs);
                        else
                                bs->eobs = TRUE;
                        bs->byteidx = 0;
                }
        }
        *retval = bit;
        return TRUE;
}

/*read N bits from the bit stream */
int getbits(bitstream *bs, unsigned int *retval, int N)
{
        unsigned int val = 0;
        int i = N;
        unsigned int j;

        // Optimize: we are on byte boundary and want to read multiple of bytes!
        if ((bs->bitidx == 8) && ((N & 7) == 0)) {
                i = N >> 3;
                while (i > 0) {
                        if (bs->eobs)
                                return FALSE;
                        val = (val << 8) | bs->bfr[bs->byteidx];
                        bs->byteidx++;
                        bs->totbits += 8;
                        if (bs->byteidx == bs->bufcount) {
                                if (bs->bufcount == BUFFER_SIZE)
                                        refill_buffer(bs);
                                else
                                        bs->eobs = TRUE;
                                bs->byteidx = 0;
                        }
                        i--;
                }
        } else {
                while (i > 0) {
                        if (bs->eobs)
                                return FALSE;

                        j = (bs->bfr[bs->byteidx] & masks[bs->bitidx - 1]) >> (bs->bitidx - 1);
                        bs->totbits++;
                        bs->bitidx--;
                        if (!bs->bitidx) {
                                bs->bitidx = 8;
                                bs->byteidx++;
                                if (bs->byteidx == bs->bufcount) {
                                        if (bs->bufcount == BUFFER_SIZE)
                                                refill_buffer(bs);
                                        else
                                                bs->eobs = TRUE;
                                        bs->byteidx = 0;
                                }
                        }
                        val = (val << 1) | j;
                        i--;
                }
        }
        *retval = val;
        return TRUE;
}

/*return the status of the bit stream*/
/* returns 1 if end of bit stream was reached */
/* returns 0 if end of bit stream was not reached */

int end_bs(bitstream *bs)
{
        return bs->eobs;
}

/*this function seeks for a byte aligned sync word (max 32 bits) in the bit stream and
  places the bit stream pointer right after the sync.
  This function returns 1 if the sync was found otherwise it returns 0  */

int seek_sync(bitstream *bs, unsigned int sync, int N)
{
        unsigned int val, val1;
        unsigned int maxi = (int)pow(2.0, (double)N) - 1;

        while (bs->bitidx != 8)
                if (!get1bit(bs, &val))
                        return FALSE;
        if (!getbits(bs, &val, N))
                return FALSE;

        while ((val & maxi) != sync) {
                val <<= 8;
                if (!getbits(bs, &val1, 8))
                        return FALSE;
                val |= val1;
        }
        return TRUE;
}