The Tor Browser: comparison media/libjpeg/jdmainct.c

--1:000000000000
+:044bd26f044c
+/*
+* 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));
+}
+}

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media/libjpeg/jdmainct.c