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 /*

  * jdmainct.c

  *

  * This file was part of the Independent JPEG Group's software:

  * Copyright (C) 1994-1996, Thomas G. Lane.

  * libjpeg-turbo Modifications:

  * Copyright (C) 2010, D. R. Commander.

  * 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"

 #include "jpegcomp.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 * DCT_scaled_size / min_DCT_scaled_size)

  * sample rows of each component.  (We require DCT_scaled_size values to be

  * chosen such that these numbers are integers.  In practice DCT_scaled_size

  * values will likely be powers of two, so we actually have the stronger

  * condition that DCT_scaled_size / min_DCT_scaled_size 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 coefficient controller will deliver data to us one iMCU row at a time;

  * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or

  * exactly min_DCT_scaled_size 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 DCT_scaled_size 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_DCT_scaled_size 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_DCT_scaled_size 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_DCT_scaled_size 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 main_ptr = (my_main_ptr) cinfo->main;

   int ci, rgroup;

   int M = cinfo->_min_DCT_scaled_size;

   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.

    */

   main_ptr->xbuffer[0] = (JSAMPIMAGE)

     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));

   main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components;

   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

        ci++, compptr++) {

     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /

       cinfo->_min_DCT_scaled_size; /* 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 */

     main_ptr->xbuffer[0][ci] = xbuf;

     xbuf += rgroup * (M + 4);

     main_ptr->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 main_ptr->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 main_ptr = (my_main_ptr) cinfo->main;

   int ci, i, rgroup;

   int M = cinfo->_min_DCT_scaled_size;

   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->_DCT_scaled_size) /

       cinfo->_min_DCT_scaled_size; /* height of a row group of component */

     xbuf0 = main_ptr->xbuffer[0][ci];

     xbuf1 = main_ptr->xbuffer[1][ci];

     /* First copy the workspace pointers as-is */

     buf = main_ptr->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 main_ptr = (my_main_ptr) cinfo->main;

   int ci, i, rgroup;

   int M = cinfo->_min_DCT_scaled_size;

   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->_DCT_scaled_size) /

       cinfo->_min_DCT_scaled_size; /* height of a row group of component */

     xbuf0 = main_ptr->xbuffer[0][ci];

     xbuf1 = main_ptr->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 main_ptr = (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->_DCT_scaled_size;

     rgroup = iMCUheight / cinfo->_min_DCT_scaled_size;

     /* 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) {

       main_ptr->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 = main_ptr->xbuffer[main_ptr->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 main_ptr = (my_main_ptr) cinfo->main;

   switch (pass_mode) {

   case JBUF_PASS_THRU:

     if (cinfo->upsample->need_context_rows) {

       main_ptr->pub.process_data = process_data_context_main;

       make_funny_pointers(cinfo); /* Create the xbuffer[] lists */

       main_ptr->whichptr = 0;	/* Read first iMCU row into xbuffer[0] */

       main_ptr->context_state = CTX_PREPARE_FOR_IMCU;

       main_ptr->iMCU_row_ctr = 0;

     } else {

       /* Simple case with no context needed */

       main_ptr->pub.process_data = process_data_simple_main;

     }

     main_ptr->buffer_full = FALSE;	/* Mark buffer empty */

     main_ptr->rowgroup_ctr = 0;

     break;

 #ifdef QUANT_2PASS_SUPPORTED

   case JBUF_CRANK_DEST:

     /* For last pass of 2-pass quantization, just crank the postprocessor */

     main_ptr->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 main_ptr = (my_main_ptr) cinfo->main;

   JDIMENSION rowgroups_avail;

   /* Read input data if we haven't filled the main buffer yet */

   if (! main_ptr->buffer_full) {

     if (! (*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer))

       return;			/* suspension forced, can do nothing more */

     main_ptr->buffer_full = TRUE;	/* OK, we have an iMCU row to work with */

   }

   /* There are always min_DCT_scaled_size row groups in an iMCU row. */

   rowgroups_avail = (JDIMENSION) cinfo->_min_DCT_scaled_size;

   /* 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, main_ptr->buffer,

 				     &main_ptr->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 (main_ptr->rowgroup_ctr >= rowgroups_avail) {

     main_ptr->buffer_full = FALSE;

     main_ptr->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 main_ptr = (my_main_ptr) cinfo->main;

   /* Read input data if we haven't filled the main buffer yet */

   if (! main_ptr->buffer_full) {

     if (! (*cinfo->coef->decompress_data) (cinfo,

 					   main_ptr->xbuffer[main_ptr->whichptr]))

       return;			/* suspension forced, can do nothing more */

     main_ptr->buffer_full = TRUE;	/* OK, we have an iMCU row to work with */

     main_ptr->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 (main_ptr->context_state) {

   case CTX_POSTPONED_ROW:

     /* Call postprocessor using previously set pointers for postponed row */

     (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],

 			&main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,

 			output_buf, out_row_ctr, out_rows_avail);

     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)

       return;			/* Need to suspend */

     main_ptr->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 */

     main_ptr->rowgroup_ctr = 0;

     main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size - 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 (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows)

       set_bottom_pointers(cinfo);

     main_ptr->context_state = CTX_PROCESS_IMCU;

     /*FALLTHROUGH*/

   case CTX_PROCESS_IMCU:

     /* Call postprocessor using previously set pointers */

     (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],

 			&main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,

 			output_buf, out_row_ctr, out_rows_avail);

     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)

       return;			/* Need to suspend */

     /* After the first iMCU, change wraparound pointers to normal state */

     if (main_ptr->iMCU_row_ctr == 1)

       set_wraparound_pointers(cinfo);

     /* Prepare to load new iMCU row using other xbuffer list */

     main_ptr->whichptr ^= 1;	/* 0=>1 or 1=>0 */

     main_ptr->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 */

     main_ptr->rowgroup_ctr = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 1);

     main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 2);

     main_ptr->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 main_ptr;

   int ci, rgroup, ngroups;

   jpeg_component_info *compptr;

   main_ptr = (my_main_ptr)

     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				SIZEOF(my_main_controller));

   cinfo->main = (struct jpeg_d_main_controller *) main_ptr;

   main_ptr->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_DCT_scaled_size < 2) /* unsupported, see comments above */

       ERREXIT(cinfo, JERR_NOTIMPL);

     alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */

     ngroups = cinfo->_min_DCT_scaled_size + 2;

   } else {

     ngroups = cinfo->_min_DCT_scaled_size;

   }

   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;

        ci++, compptr++) {

     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /

       cinfo->_min_DCT_scaled_size; /* height of a row group of component */

     main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)

 			((j_common_ptr) cinfo, JPOOL_IMAGE,

 			 compptr->width_in_blocks * compptr->_DCT_scaled_size,

 			 (JDIMENSION) (rgroup * ngroups));

   }

 }