/*
 * 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, 2016, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * 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.
 */

#include "jinclude.h"
#include "jdmainct.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.
 */


/* Forward declarations */
METHODDEF(void) process_data_simple_main
		(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
		 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail);

METHODDEF(void) process_data_context_main
		(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
		(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_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));
	}
}
