The Tor Browser: media/libjpeg/jdmainct.c@b8a032363ba2 (annotated)

media/libjpeg/jdmainct.c@b8a032363ba2 (annotated)

media/libjpeg/jdmainct.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /*
  * 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,
 * (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));
   }
 }

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media/libjpeg/jdmainct.c@b8a032363ba2 (annotated)

media/libjpeg/jdmainct.c