text: /*
   * jdmainct.c
   *
   * Copyright (C) 1994-1998, Thomas G. Lane.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This file contains the main buffer controller for decompression.
   * The main buffer lies between the JPEG decompressor proper and the
   * post-processor; it holds downsampled data in the JPEG colorspace.
   *
   * Note that this code is bypassed in raw-data mode, since the application
   * supplies the equivalent of the main buffer in that case.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  
  
  /*
   * In the current system design, the main buffer need never be a full-image
   * buffer; any full-height buffers will be found inside the coefficient or
   * postprocessing controllers.  Nonetheless, the main controller is not
   * trivial.  Its responsibility is to provide context rows for upsampling/
   * rescaling, and doing this in an efficient fashion is a bit tricky.
   *
   * Postprocessor input data is counted in "row groups".  A row group
   * is defined to be (v_samp_factor * codec_data_unit / min_codec_data_unit)
   * sample rows of each component.  (We require codec_data_unit values to be
   * chosen such that these numbers are integers.  In practice codec_data_unit
   * values will likely be powers of two, so we actually have the stronger
   * condition that codec_data_unit / min_codec_data_unit is an integer.)
   * Upsampling will typically produce max_v_samp_factor pixel rows from each
   * row group (times any additional scale factor that the upsampler is
   * applying).
   *
   * The decompression codec will deliver data to us one iMCU row at a time;
   * each iMCU row contains v_samp_factor * codec_data_unit sample rows, or
   * exactly min_codec_data_unit row groups.  (This amount of data corresponds
   * to one row of MCUs when the image is fully interleaved.)  Note that the
   * number of sample rows varies across components, but the number of row
   * groups does not.  Some garbage sample rows may be included in the last iMCU
   * row at the bottom of the image.
   *
   * Depending on the vertical scaling algorithm used, the upsampler may need
   * access to the sample row(s) above and below its current input row group.
   * The upsampler is required to set need_context_rows TRUE at global selection
   * time if so.  When need_context_rows is FALSE, this controller can simply
   * obtain one iMCU row at a time from the coefficient controller and dole it
   * out as row groups to the postprocessor.
   *
   * When need_context_rows is TRUE, this controller guarantees that the buffer
   * passed to postprocessing contains at least one row group's worth of samples
   * above and below the row group(s) being processed.  Note that the context
   * rows "above" the first passed row group appear at negative row offsets in
   * the passed buffer.  At the top and bottom of the image, the required
   * context rows are manufactured by duplicating the first or last real sample
   * row; this avoids having special cases in the upsampling inner loops.
   *
   * The amount of context is fixed at one row group just because that's a
   * convenient number for this controller to work with.  The existing
   * upsamplers really only need one sample row of context.  An upsampler
   * supporting arbitrary output rescaling might wish for more than one row
   * group of context when shrinking the image; tough, we don't handle that.
   * (This is justified by the assumption that downsizing will be handled mostly
   * by adjusting the codec_data_unit values, so that the actual scale factor at
   * the upsample step needn't be much less than one.)
   *
   * To provide the desired context, we have to retain the last two row groups
   * of one iMCU row while reading in the next iMCU row.  (The last row group
   * can't be processed until we have another row group for its below-context,
   * and so we have to save the next-to-last group too for its above-context.)
   * We could do this most simply by copying data around in our buffer, but
   * that'd be very slow.  We can avoid copying any data by creating a rather
   * strange pointer structure.  Here's how it works.  We allocate a workspace
   * consisting of M+2 row groups (where M = min_codec_data_unit is the number
   * of row groups per iMCU row).  We create two sets of redundant pointers to
   * the workspace.  Labeling the physical row groups 0 to M+1, the synthesized
   * pointer lists look like this:
   *                   M+1                          M-1
   * master pointer --> 0         master pointer --> 0
   *                    1                            1
   *                   ...                          ...
   *                   M-3                          M-3
   *                   M-2                           M
   *                   M-1                          M+1
   *                    M                           M-2
   *                   M+1                          M-1
   *                    0                            0
   * We read alternate iMCU rows using each master pointer; thus the last two
   * row groups of the previous iMCU row remain un-overwritten in the workspace.
   * The pointer lists are set up so that the required context rows appear to
   * be adjacent to the proper places when we pass the pointer lists to the
   * upsampler.
   *
   * The above pictures describe the normal state of the pointer lists.
   * At top and bottom of the image, we diddle the pointer lists to duplicate
   * the first or last sample row as necessary (this is cheaper than copying
   * sample rows around).
   *
   * This scheme breaks down if M < 2, ie, min_codec_data_unit is 1.  In that
   * situation each iMCU row provides only one row group so the buffering logic
   * must be different (eg, we must read two iMCU rows before we can emit the
   * first row group).  For now, we simply do not support providing context
   * rows when min_codec_data_unit is 1.  That combination seems unlikely to
   * be worth providing --- if someone wants a 1/8th-size preview, they probably
   * want it quick and dirty, so a context-free upsampler is sufficient.
   */
  
  
  /* Private buffer controller object */
  
  typedef struct {
    struct jpeg_d_main_controller pub; /* public fields */
  
    /* Pointer to allocated workspace (M or M+2 row groups). */
    JSAMPARRAY buffer[MAX_COMPONENTS];
  
    boolean buffer_full;		/* Have we gotten an iMCU row from decoder? */
    JDIMENSION rowgroup_ctr;	/* counts row groups output to postprocessor */
  
    /* Remaining fields are only used in the context case. */
  
    /* These are the master pointers to the funny-order pointer lists. */
    JSAMPIMAGE xbuffer[2];	/* pointers to weird pointer lists */
  
    int whichptr;			/* indicates which pointer set is now in use */
    int context_state;		/* process_data state machine status */
    JDIMENSION rowgroups_avail;	/* row groups available to postprocessor */
    JDIMENSION iMCU_row_ctr;	/* counts iMCU rows to detect image top/bot */
  } my_main_controller;
  
  typedef my_main_controller * my_main_ptr;
  
  /* context_state values: */
  #define CTX_PREPARE_FOR_IMCU	0	/* need to prepare for MCU row */
  #define CTX_PROCESS_IMCU	1	/* feeding iMCU to postprocessor */
  #define CTX_POSTPONED_ROW	2	/* feeding postponed row group */
  
  
  /* Forward declarations */
  METHODDEF(void) process_data_simple_main
  	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
  METHODDEF(void) process_data_context_main
  	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
  #ifdef QUANT_2PASS_SUPPORTED
  METHODDEF(void) process_data_crank_post
  	JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
  	     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
  #endif
  
  
  LOCAL(void)
  alloc_funny_pointers (j_decompress_ptr cinfo)
  /* Allocate space for the funny pointer lists.
   * This is done only once, not once per pass.
   */
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
    int ci, rgroup;
    int M = cinfo->min_codec_data_unit;
    jpeg_component_info *compptr;
    JSAMPARRAY xbuf;
  
    /* Get top-level space for component array pointers.
     * We alloc both arrays with one call to save a few cycles.
     */
    mainPtr->xbuffer[0] = (JSAMPIMAGE)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
    mainPtr->xbuffer[1] = mainPtr->xbuffer[0] + cinfo->num_components;
  
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
         ci++, compptr++) {
      rgroup = (compptr->v_samp_factor * compptr->codec_data_unit) /
        cinfo->min_codec_data_unit; /* height of a row group of component */
      /* Get space for pointer lists --- M+4 row groups in each list.
       * We alloc both pointer lists with one call to save a few cycles.
       */
      xbuf = (JSAMPARRAY)
        (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				  2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
      xbuf += rgroup;		/* want one row group at negative offsets */
      mainPtr->xbuffer[0][ci] = xbuf;
      xbuf += rgroup * (M + 4);
      mainPtr->xbuffer[1][ci] = xbuf;
    }
  }
  
  
  LOCAL(void)
  make_funny_pointers (j_decompress_ptr cinfo)
  /* Create the funny pointer lists discussed in the comments above.
   * The actual workspace is already allocated (in mainPtr->buffer),
   * and the space for the pointer lists is allocated too.
   * This routine just fills in the curiously ordered lists.
   * This will be repeated at the beginning of each pass.
   */
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
    int ci, i, rgroup;
    int M = cinfo->min_codec_data_unit;
    jpeg_component_info *compptr;
    JSAMPARRAY buf, xbuf0, xbuf1;
  
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
         ci++, compptr++) {
      rgroup = (compptr->v_samp_factor * compptr->codec_data_unit) /
        cinfo->min_codec_data_unit; /* height of a row group of component */
      xbuf0 = mainPtr->xbuffer[0][ci];
      xbuf1 = mainPtr->xbuffer[1][ci];
      /* First copy the workspace pointers as-is */
      buf = mainPtr->buffer[ci];
      for (i = 0; i < rgroup * (M + 2); i++) {
        xbuf0[i] = xbuf1[i] = buf[i];
      }
      /* In the second list, put the last four row groups in swapped order */
      for (i = 0; i < rgroup * 2; i++) {
        xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
        xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
      }
      /* The wraparound pointers at top and bottom will be filled later
       * (see set_wraparound_pointers, below).  Initially we want the "above"
       * pointers to duplicate the first actual data line.  This only needs
       * to happen in xbuffer[0].
       */
      for (i = 0; i < rgroup; i++) {
        xbuf0[i - rgroup] = xbuf0[0];
      }
    }
  }
  
  
  LOCAL(void)
  set_wraparound_pointers (j_decompress_ptr cinfo)
  /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
   * This changes the pointer list state from top-of-image to the normal state.
   */
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
    int ci, i, rgroup;
    int M = cinfo->min_codec_data_unit;
    jpeg_component_info *compptr;
    JSAMPARRAY xbuf0, xbuf1;
  
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
         ci++, compptr++) {
      rgroup = (compptr->v_samp_factor * compptr->codec_data_unit) /
        cinfo->min_codec_data_unit; /* height of a row group of component */
      xbuf0 = mainPtr->xbuffer[0][ci];
      xbuf1 = mainPtr->xbuffer[1][ci];
      for (i = 0; i < rgroup; i++) {
        xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
        xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
        xbuf0[rgroup*(M+2) + i] = xbuf0[i];
        xbuf1[rgroup*(M+2) + i] = xbuf1[i];
      }
    }
  }
  
  
  LOCAL(void)
  set_bottom_pointers (j_decompress_ptr cinfo)
  /* Change the pointer lists to duplicate the last sample row at the bottom
   * of the image.  whichptr indicates which xbuffer holds the final iMCU row.
   * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
   */
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
    int ci, i, rgroup, iMCUheight, rows_left;
    jpeg_component_info *compptr;
    JSAMPARRAY xbuf;
  
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
         ci++, compptr++) {
      /* Count sample rows in one iMCU row and in one row group */
      iMCUheight = compptr->v_samp_factor * compptr->codec_data_unit;
      rgroup = iMCUheight / cinfo->min_codec_data_unit;
      /* Count nondummy sample rows remaining for this component */
      rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
      if (rows_left == 0) rows_left = iMCUheight;
      /* Count nondummy row groups.  Should get same answer for each component,
       * so we need only do it once.
       */
      if (ci == 0) {
        mainPtr->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
      }
      /* Duplicate the last real sample row rgroup*2 times; this pads out the
       * last partial rowgroup and ensures at least one full rowgroup of context.
       */
      xbuf = mainPtr->xbuffer[mainPtr->whichptr][ci];
      for (i = 0; i < rgroup * 2; i++) {
        xbuf[rows_left + i] = xbuf[rows_left-1];
      }
    }
  }
  
  
  /*
   * Initialize for a processing pass.
   */
  
  METHODDEF(void)
  start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
  
    switch (pass_mode) {
    case JBUF_PASS_THRU:
      if (cinfo->upsample->need_context_rows) {
        mainPtr->pub.process_data = process_data_context_main;
        make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
        mainPtr->whichptr = 0;  /* Read first iMCU row into xbuffer[0] */
        mainPtr->context_state = CTX_PREPARE_FOR_IMCU;
        mainPtr->iMCU_row_ctr = 0;
      } else {
        /* Simple case with no context needed */
        mainPtr->pub.process_data = process_data_simple_main;
      }
      mainPtr->buffer_full = FALSE;  /* Mark buffer empty */
      mainPtr->rowgroup_ctr = 0;
      break;
  #ifdef QUANT_2PASS_SUPPORTED
    case JBUF_CRANK_DEST:
      /* For last pass of 2-pass quantization, just crank the postprocessor */
      mainPtr->pub.process_data = process_data_crank_post;
      break;
  #endif
    default:
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
      break;
    }
  }
  
  
  /*
   * Process some data.
   * This handles the simple case where no context is required.
   */
  
  METHODDEF(void)
  process_data_simple_main (j_decompress_ptr cinfo,
  			  JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
  			  JDIMENSION out_rows_avail)
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
    JDIMENSION rowgroups_avail;
  
    /* Read input data if we haven't filled the main buffer yet */
    if (! mainPtr->buffer_full) {
      if (! (*cinfo->codec->decompress_data) (cinfo, mainPtr->buffer))
        return;			/* suspension forced, can do nothing more */
      mainPtr->buffer_full = TRUE;  /* OK, we have an iMCU row to work with */
    }
  
    /* There are always min_codec_data_unit row groups in an iMCU row. */
    rowgroups_avail = (JDIMENSION) cinfo->min_codec_data_unit;
    /* Note: at the bottom of the image, we may pass extra garbage row groups
     * to the postprocessor.  The postprocessor has to check for bottom
     * of image anyway (at row resolution), so no point in us doing it too.
     */
  
    /* Feed the postprocessor */
    (*cinfo->post->post_process_data) (cinfo, mainPtr->buffer,
               &mainPtr->rowgroup_ctr, rowgroups_avail,
  				     output_buf, out_row_ctr, out_rows_avail);
  
    /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
    if (mainPtr->rowgroup_ctr >= rowgroups_avail) {
      mainPtr->buffer_full = FALSE;
      mainPtr->rowgroup_ctr = 0;
    }
  }
  
  
  /*
   * Process some data.
   * This handles the case where context rows must be provided.
   */
  
  METHODDEF(void)
  process_data_context_main (j_decompress_ptr cinfo,
  			   JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
  			   JDIMENSION out_rows_avail)
  {
    my_main_ptr mainPtr = (my_main_ptr) cinfo->main;
  
    /* Read input data if we haven't filled the main buffer yet */
    if (! mainPtr->buffer_full) {
      if (! (*cinfo->codec->decompress_data) (cinfo,
               mainPtr->xbuffer[mainPtr->whichptr]))
        return;			/* suspension forced, can do nothing more */
      mainPtr->buffer_full = TRUE;  /* OK, we have an iMCU row to work with */
      mainPtr->iMCU_row_ctr++;  /* count rows received */
    }
  
    /* Postprocessor typically will not swallow all the input data it is handed
     * in one call (due to filling the output buffer first).  Must be prepared
     * to exit and restart.  This switch lets us keep track of how far we got.
     * Note that each case falls through to the next on successful completion.
     */
    switch (mainPtr->context_state) {
    case CTX_POSTPONED_ROW:
      /* Call postprocessor using previously set pointers for postponed row */
      (*cinfo->post->post_process_data) (cinfo, mainPtr->xbuffer[mainPtr->whichptr],
        &mainPtr->rowgroup_ctr, mainPtr->rowgroups_avail,
  			output_buf, out_row_ctr, out_rows_avail);
      if (mainPtr->rowgroup_ctr < mainPtr->rowgroups_avail)
        return;			/* Need to suspend */
      mainPtr->context_state = CTX_PREPARE_FOR_IMCU;
      if (*out_row_ctr >= out_rows_avail)
        return;			/* Postprocessor exactly filled output buf */
      /*FALLTHROUGH*/
    case CTX_PREPARE_FOR_IMCU:
      /* Prepare to process first M-1 row groups of this iMCU row */
      mainPtr->rowgroup_ctr = 0;
      mainPtr->rowgroups_avail = (JDIMENSION) (cinfo->min_codec_data_unit - 1);
      /* Check for bottom of image: if so, tweak pointers to "duplicate"
       * the last sample row, and adjust rowgroups_avail to ignore padding rows.
       */
      if (mainPtr->iMCU_row_ctr == cinfo->total_iMCU_rows)
        set_bottom_pointers(cinfo);
      mainPtr->context_state = CTX_PROCESS_IMCU;
      /*FALLTHROUGH*/
    case CTX_PROCESS_IMCU:
      /* Call postprocessor using previously set pointers */
      (*cinfo->post->post_process_data) (cinfo, mainPtr->xbuffer[mainPtr->whichptr],
        &mainPtr->rowgroup_ctr, mainPtr->rowgroups_avail,
  			output_buf, out_row_ctr, out_rows_avail);
      if (mainPtr->rowgroup_ctr < mainPtr->rowgroups_avail)
        return;			/* Need to suspend */
      /* After the first iMCU, change wraparound pointers to normal state */
      if (mainPtr->iMCU_row_ctr == 1)
        set_wraparound_pointers(cinfo);
      /* Prepare to load new iMCU row using other xbuffer list */
      mainPtr->whichptr ^= 1;  /* 0=>1 or 1=>0 */
      mainPtr->buffer_full = FALSE;
      /* Still need to process last row group of this iMCU row, */
      /* which is saved at index M+1 of the other xbuffer */
      mainPtr->rowgroup_ctr = (JDIMENSION) (cinfo->min_codec_data_unit + 1);
      mainPtr->rowgroups_avail = (JDIMENSION) (cinfo->min_codec_data_unit + 2);
      mainPtr->context_state = CTX_POSTPONED_ROW;
    }
  }
  
  
  /*
   * Process some data.
   * Final pass of two-pass quantization: just call the postprocessor.
   * Source data will be the postprocessor controller's internal buffer.
   */
  
  #ifdef QUANT_2PASS_SUPPORTED
  
  METHODDEF(void)
  process_data_crank_post (j_decompress_ptr cinfo,
  			 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
  			 JDIMENSION out_rows_avail)
  {
    (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
  				     (JDIMENSION *) NULL, (JDIMENSION) 0,
  				     output_buf, out_row_ctr, out_rows_avail);
  }
  
  #endif /* QUANT_2PASS_SUPPORTED */
  
  
  /*
   * Initialize main buffer controller.
   */
  
  GLOBAL(void)
  jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
  {
    my_main_ptr mainPtr;
    int ci, rgroup, ngroups;
    jpeg_component_info *compptr;
  
    mainPtr = (my_main_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				SIZEOF(my_main_controller));
    cinfo->main = (struct jpeg_d_main_controller *) mainPtr;
    mainPtr->pub.start_pass = start_pass_main;
  
    if (need_full_buffer)		/* shouldn't happen */
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
  
    /* Allocate the workspace.
     * ngroups is the number of row groups we need.
     */
    if (cinfo->upsample->need_context_rows) {
      if (cinfo->min_codec_data_unit < 2) /* unsupported, see comments above */
        ERREXIT(cinfo, JERR_NOTIMPL);
      alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
      ngroups = cinfo->min_codec_data_unit + 2;
    } else {
      ngroups = cinfo->min_codec_data_unit;
    }
  
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
         ci++, compptr++) {
      rgroup = (compptr->v_samp_factor * compptr->codec_data_unit) /
        cinfo->min_codec_data_unit; /* height of a row group of component */
      mainPtr->buffer[ci] = (*cinfo->mem->alloc_sarray)
  			((j_common_ptr) cinfo, JPOOL_IMAGE,
  			 compptr->width_in_data_units * compptr->codec_data_unit,
  			 (JDIMENSION) (rgroup * ngroups));
    }
  }
  