/src/gdal/build/frmts/jpeg/libjpeg12/jcprepct12.c

Source (jump to first uncovered line)
/*
 * jcprepct.c
 *
 * Copyright (C) 1994-1996, 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 compression preprocessing controller.
 * This controller manages the color conversion, downsampling,
 * and edge expansion steps.
 *
 * Most of the complexity here is associated with buffering input rows
 * as required by the downsampler.  See the comments at the head of
 * jcsample.c for the downsampler's needs.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* At present, jcsample.c can request context rows only for smoothing.
 * In the future, we might also need context rows for CCIR601 sampling
 * or other more-complex downsampling procedures.  The code to support
 * context rows should be compiled only if needed.
 */
#ifdef INPUT_SMOOTHING_SUPPORTED
#define CONTEXT_ROWS_SUPPORTED
#endif


/*
 * For the simple (no-context-row) case, we just need to buffer one
 * row group's worth of pixels for the downsampling step.  At the bottom of
 * the image, we pad to a full row group by replicating the last pixel row.
 * The downsampler's last output row is then replicated if needed to pad
 * out to a full iMCU row.
 *
 * When providing context rows, we must buffer three row groups' worth of
 * pixels.  Three row groups are physically allocated, but the row pointer
 * arrays are made five row groups high, with the extra pointers above and
 * below "wrapping around" to point to the last and first real row groups.
 * This allows the downsampler to access the proper context rows.
 * At the top and bottom of the image, we create dummy context rows by
 * copying the first or last real pixel row.  This copying could be avoided
 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
 * trouble on the compression side.
 */


/* Private buffer controller object */

typedef struct {
  struct jpeg_c_prep_controller pub; /* public fields */

  /* Downsampling input buffer.  This buffer holds color-converted data
   * until we have enough to do a downsample step.
   */
  JSAMPARRAY color_buf[MAX_COMPONENTS];

  JDIMENSION rows_to_go;  /* counts rows remaining in source image */
  int next_buf_row;   /* index of next row to store in color_buf */

#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
  int this_row_group;   /* starting row index of group to process */
  int next_buf_stop;    /* downsample when we reach this index */
#endif
} my_prep_controller;

typedef my_prep_controller * my_prep_ptr;


/*
 * Initialize for a processing pass.
 */

METHODDEF(void)
start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;

  if (pass_mode != JBUF_PASS_THRU)
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

  /* Initialize total-height counter for detecting bottom of image */
  prep->rows_to_go = cinfo->image_height;
  /* Mark the conversion buffer empty */
  prep->next_buf_row = 0;
#ifdef CONTEXT_ROWS_SUPPORTED
  /* Preset additional state variables for context mode.
   * These aren't used in non-context mode, so we needn't test which mode.
   */
  prep->this_row_group = 0;
  /* Set next_buf_stop to stop after two row groups have been read in. */
  prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
#endif
}


/*
 * Expand an image vertically from height input_rows to height output_rows,
 * by duplicating the bottom row.
 */

LOCAL(void)
expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
        int input_rows, int output_rows)
{
  register int row;

  for (row = input_rows; row < output_rows; row++) {
    jcopy_sample_rows(image_data, input_rows-1, image_data, row,
          1, num_cols);
  }
}


/*
 * Process some data in the simple no-context case.
 *
 * Preprocessor output data is counted in "row groups".  A row group
 * is defined to be v_samp_factor sample rows of each component.
 * Downsampling will produce this much data from each max_v_samp_factor
 * input rows.
 */

METHODDEF(void)
pre_process_data (j_compress_ptr cinfo,
      JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
      JDIMENSION in_rows_avail,
      JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
      JDIMENSION out_row_groups_avail)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int numrows, ci;
  JDIMENSION inrows;
  jpeg_component_info * compptr;

  while (*in_row_ctr < in_rows_avail &&
   *out_row_group_ctr < out_row_groups_avail) {
    /* Do color conversion to fill the conversion buffer. */
    inrows = in_rows_avail - *in_row_ctr;
    numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
    numrows = (int) MIN((JDIMENSION) numrows, inrows);
    (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
               prep->color_buf,
               (JDIMENSION) prep->next_buf_row,
               numrows);
    *in_row_ctr += numrows;
    prep->next_buf_row += numrows;
    prep->rows_to_go -= numrows;
    /* If at bottom of image, pad to fill the conversion buffer. */
    if (prep->rows_to_go == 0 &&
  prep->next_buf_row < cinfo->max_v_samp_factor) {
      for (ci = 0; ci < cinfo->num_components; ci++) {
  expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
         prep->next_buf_row, cinfo->max_v_samp_factor);
      }
      prep->next_buf_row = cinfo->max_v_samp_factor;
    }
    /* If we've filled the conversion buffer, empty it. */
    if (prep->next_buf_row == cinfo->max_v_samp_factor) {
      (*cinfo->downsample->downsample) (cinfo,
          prep->color_buf, (JDIMENSION) 0,
          output_buf, *out_row_group_ctr);
      prep->next_buf_row = 0;
      (*out_row_group_ctr)++;
    }
    /* If at bottom of image, pad the output to a full iMCU height.
     * Note we assume the caller is providing a one-iMCU-height output buffer!
     */
    if (prep->rows_to_go == 0 &&
  *out_row_group_ctr < out_row_groups_avail) {
      for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
     ci++, compptr++) {
  expand_bottom_edge(output_buf[ci],
         compptr->width_in_blocks * DCTSIZE,
         (int) (*out_row_group_ctr * compptr->v_samp_factor),
         (int) (out_row_groups_avail * compptr->v_samp_factor));
      }
      *out_row_group_ctr = out_row_groups_avail;
      break;      /* can exit outer loop without test */
    }
  }
}


#ifdef CONTEXT_ROWS_SUPPORTED

/*
 * Process some data in the context case.
 */

METHODDEF(void)
pre_process_context (j_compress_ptr cinfo,
         JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
         JDIMENSION in_rows_avail,
         JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
         JDIMENSION out_row_groups_avail)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int numrows, ci;
  int buf_height = cinfo->max_v_samp_factor * 3;
  JDIMENSION inrows;

  while (*out_row_group_ctr < out_row_groups_avail) {
    if (*in_row_ctr < in_rows_avail) {
      /* Do color conversion to fill the conversion buffer. */
      inrows = in_rows_avail - *in_row_ctr;
      numrows = prep->next_buf_stop - prep->next_buf_row;
      numrows = (int) MIN((JDIMENSION) numrows, inrows);
      (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
           prep->color_buf,
           (JDIMENSION) prep->next_buf_row,
           numrows);
      /* Pad at top of image, if first time through */
      if (prep->rows_to_go == cinfo->image_height) {
  for (ci = 0; ci < cinfo->num_components; ci++) {
    int row;
    for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
      jcopy_sample_rows(prep->color_buf[ci], 0,
            prep->color_buf[ci], -row,
            1, cinfo->image_width);
    }
  }
      }
      *in_row_ctr += numrows;
      prep->next_buf_row += numrows;
      prep->rows_to_go -= numrows;
    } else {
      /* Return for more data, unless we are at the bottom of the image. */
      if (prep->rows_to_go != 0)
  break;
      /* When at bottom of image, pad to fill the conversion buffer. */
      if (prep->next_buf_row < prep->next_buf_stop) {
  for (ci = 0; ci < cinfo->num_components; ci++) {
    expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
           prep->next_buf_row, prep->next_buf_stop);
  }
  prep->next_buf_row = prep->next_buf_stop;
      }
    }
    /* If we've gotten enough data, downsample a row group. */
    if (prep->next_buf_row == prep->next_buf_stop) {
      (*cinfo->downsample->downsample) (cinfo,
          prep->color_buf,
          (JDIMENSION) prep->this_row_group,
          output_buf, *out_row_group_ctr);
      (*out_row_group_ctr)++;
      /* Advance pointers with wraparound as necessary. */
      prep->this_row_group += cinfo->max_v_samp_factor;
      if (prep->this_row_group >= buf_height)
  prep->this_row_group = 0;
      if (prep->next_buf_row >= buf_height)
  prep->next_buf_row = 0;
      prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
    }
  }
}


/*
 * Create the wrapped-around downsampling input buffer needed for context mode.
 */

LOCAL(void)
create_context_buffer (j_compress_ptr cinfo)
{
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  int rgroup_height = cinfo->max_v_samp_factor;
  int ci, i;
  jpeg_component_info * compptr;
  JSAMPARRAY true_buffer, fake_buffer;

  /* Grab enough space for fake row pointers for all the components;
   * we need five row groups' worth of pointers for each component.
   */
  fake_buffer = (JSAMPARRAY)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
        (cinfo->num_components * 5 * rgroup_height) *
        SIZEOF(JSAMPROW));

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    /* Allocate the actual buffer space (3 row groups) for this component.
     * We make the buffer wide enough to allow the downsampler to edge-expand
     * horizontally within the buffer, if it so chooses.
     */
    true_buffer = (*cinfo->mem->alloc_sarray)
      ((j_common_ptr) cinfo, JPOOL_IMAGE,
       (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
          cinfo->max_h_samp_factor) / compptr->h_samp_factor),
       (JDIMENSION) (3 * rgroup_height));
    /* Copy true buffer row pointers into the middle of the fake row array */
    MEMCOPY(fake_buffer + rgroup_height, true_buffer,
      3 * rgroup_height * SIZEOF(JSAMPROW));
    /* Fill in the above and below wraparound pointers */
    for (i = 0; i < rgroup_height; i++) {
      fake_buffer[i] = true_buffer[2 * rgroup_height + i];
      fake_buffer[4 * rgroup_height + i] = true_buffer[i];
    }
    prep->color_buf[ci] = fake_buffer + rgroup_height;
    fake_buffer += 5 * rgroup_height; /* point to space for next component */
  }
}

#endif /* CONTEXT_ROWS_SUPPORTED */


/*
 * Initialize preprocessing controller.
 */

GLOBAL(void)
jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
{
  my_prep_ptr prep;
  int ci;
  jpeg_component_info * compptr;

  if (need_full_buffer)   /* safety check */
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);

  prep = (my_prep_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
        SIZEOF(my_prep_controller));
  cinfo->prep = (struct jpeg_c_prep_controller *) prep;
  prep->pub.start_pass = start_pass_prep;

  /* Allocate the color conversion buffer.
   * We make the buffer wide enough to allow the downsampler to edge-expand
   * horizontally within the buffer, if it so chooses.
   */
  if (cinfo->downsample->need_context_rows) {
    /* Set up to provide context rows */
#ifdef CONTEXT_ROWS_SUPPORTED
    prep->pub.pre_process_data = pre_process_context;
    create_context_buffer(cinfo);
#else
    ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
  } else {
    /* No context, just make it tall enough for one row group */
    prep->pub.pre_process_data = pre_process_data;
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
   ci++, compptr++) {
      prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
  ((j_common_ptr) cinfo, JPOOL_IMAGE,
   (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
   (JDIMENSION) cinfo->max_v_samp_factor);
    }
  }
}

Coverage Report

Created: 2025-06-22 06:59

Line	Count	Source (jump to first uncovered line)
1		/*
2		* jcprepct.c
3		*
4		* Copyright (C) 1994-1996, Thomas G. Lane.
5		* This file is part of the Independent JPEG Group's software.
6		* For conditions of distribution and use, see the accompanying README file.
7		*
8		* This file contains the compression preprocessing controller.
9		* This controller manages the color conversion, downsampling,
10		* and edge expansion steps.
11		*
12		* Most of the complexity here is associated with buffering input rows
13		* as required by the downsampler. See the comments at the head of
14		* jcsample.c for the downsampler's needs.
15		*/
16
17		#define JPEG_INTERNALS
18		#include "jinclude.h"
19		#include "jpeglib.h"
20
21
22		/* At present, jcsample.c can request context rows only for smoothing.
23		* In the future, we might also need context rows for CCIR601 sampling
24		* or other more-complex downsampling procedures. The code to support
25		* context rows should be compiled only if needed.
26		*/
27		#ifdef INPUT_SMOOTHING_SUPPORTED
28		#define CONTEXT_ROWS_SUPPORTED
29		#endif
30
31
32		/*
33		* For the simple (no-context-row) case, we just need to buffer one
34		* row group's worth of pixels for the downsampling step. At the bottom of
35		* the image, we pad to a full row group by replicating the last pixel row.
36		* The downsampler's last output row is then replicated if needed to pad
37		* out to a full iMCU row.
38		*
39		* When providing context rows, we must buffer three row groups' worth of
40		* pixels. Three row groups are physically allocated, but the row pointer
41		* arrays are made five row groups high, with the extra pointers above and
42		* below "wrapping around" to point to the last and first real row groups.
43		* This allows the downsampler to access the proper context rows.
44		* At the top and bottom of the image, we create dummy context rows by
45		* copying the first or last real pixel row. This copying could be avoided
46		* by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
47		* trouble on the compression side.
48		*/
49
50
51		/* Private buffer controller object */
52
53		typedef struct {
54		struct jpeg_c_prep_controller pub; /* public fields */
55
56		/* Downsampling input buffer. This buffer holds color-converted data
57		* until we have enough to do a downsample step.
58		*/
59		JSAMPARRAY color_buf[MAX_COMPONENTS];
60
61		JDIMENSION rows_to_go; /* counts rows remaining in source image */
62		int next_buf_row; /* index of next row to store in color_buf */
63
64		#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
65		int this_row_group; /* starting row index of group to process */
66		int next_buf_stop; /* downsample when we reach this index */
67		#endif
68		} my_prep_controller;
69
70		typedef my_prep_controller * my_prep_ptr;
71
72
73		/*
74		* Initialize for a processing pass.
75		*/
76
77		METHODDEF(void)
78		start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
79	0	{
80	0	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
81
82	0	if (pass_mode != JBUF_PASS_THRU)
83	0	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
84
85		/* Initialize total-height counter for detecting bottom of image */
86	0	prep->rows_to_go = cinfo->image_height;
87		/* Mark the conversion buffer empty */
88	0	prep->next_buf_row = 0;
89	0	#ifdef CONTEXT_ROWS_SUPPORTED
90		/* Preset additional state variables for context mode.
91		* These aren't used in non-context mode, so we needn't test which mode.
92		*/
93	0	prep->this_row_group = 0;
94		/* Set next_buf_stop to stop after two row groups have been read in. */
95	0	prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
96	0	#endif
97	0	}
98
99
100		/*
101		* Expand an image vertically from height input_rows to height output_rows,
102		* by duplicating the bottom row.
103		*/
104
105		LOCAL(void)
106		expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
107		int input_rows, int output_rows)
108	0	{
109	0	register int row;
110
111	0	for (row = input_rows; row < output_rows; row++) {
112	0	jcopy_sample_rows(image_data, input_rows-1, image_data, row,
113	0	1, num_cols);
114	0	}
115	0	}
116
117
118		/*
119		* Process some data in the simple no-context case.
120		*
121		* Preprocessor output data is counted in "row groups". A row group
122		* is defined to be v_samp_factor sample rows of each component.
123		* Downsampling will produce this much data from each max_v_samp_factor
124		* input rows.
125		*/
126
127		METHODDEF(void)
128		pre_process_data (j_compress_ptr cinfo,
129		JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
130		JDIMENSION in_rows_avail,
131		JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
132		JDIMENSION out_row_groups_avail)
133	0	{
134	0	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
135	0	int numrows, ci;
136	0	JDIMENSION inrows;
137	0	jpeg_component_info * compptr;
138
139	0	while (*in_row_ctr < in_rows_avail &&
140	0	*out_row_group_ctr < out_row_groups_avail) {
141		/* Do color conversion to fill the conversion buffer. */
142	0	inrows = in_rows_avail - *in_row_ctr;
143	0	numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
144	0	numrows = (int) MIN((JDIMENSION) numrows, inrows);
145	0	(cinfo->cconvert->color_convert) (cinfo, input_buf + in_row_ctr,
146	0	prep->color_buf,
147	0	(JDIMENSION) prep->next_buf_row,
148	0	numrows);
149	0	*in_row_ctr += numrows;
150	0	prep->next_buf_row += numrows;
151	0	prep->rows_to_go -= numrows;
152		/* If at bottom of image, pad to fill the conversion buffer. */
153	0	if (prep->rows_to_go == 0 &&
154	0	prep->next_buf_row < cinfo->max_v_samp_factor) {
155	0	for (ci = 0; ci < cinfo->num_components; ci++) {
156	0	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
157	0	prep->next_buf_row, cinfo->max_v_samp_factor);
158	0	}
159	0	prep->next_buf_row = cinfo->max_v_samp_factor;
160	0	}
161		/* If we've filled the conversion buffer, empty it. */
162	0	if (prep->next_buf_row == cinfo->max_v_samp_factor) {
163	0	(*cinfo->downsample->downsample) (cinfo,
164	0	prep->color_buf, (JDIMENSION) 0,
165	0	output_buf, *out_row_group_ctr);
166	0	prep->next_buf_row = 0;
167	0	(*out_row_group_ctr)++;
168	0	}
169		/* If at bottom of image, pad the output to a full iMCU height.
170		* Note we assume the caller is providing a one-iMCU-height output buffer!
171		*/
172	0	if (prep->rows_to_go == 0 &&
173	0	*out_row_group_ctr < out_row_groups_avail) {
174	0	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
175	0	ci++, compptr++) {
176	0	expand_bottom_edge(output_buf[ci],
177	0	compptr->width_in_blocks * DCTSIZE,
178	0	(int) (out_row_group_ctr compptr->v_samp_factor),
179	0	(int) (out_row_groups_avail * compptr->v_samp_factor));
180	0	}
181	0	*out_row_group_ctr = out_row_groups_avail;
182	0	break; /* can exit outer loop without test */
183	0	}
184	0	}
185	0	}
186
187
188		#ifdef CONTEXT_ROWS_SUPPORTED
189
190		/*
191		* Process some data in the context case.
192		*/
193
194		METHODDEF(void)
195		pre_process_context (j_compress_ptr cinfo,
196		JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
197		JDIMENSION in_rows_avail,
198		JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
199		JDIMENSION out_row_groups_avail)
200	0	{
201	0	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
202	0	int numrows, ci;
203	0	int buf_height = cinfo->max_v_samp_factor * 3;
204	0	JDIMENSION inrows;
205
206	0	while (*out_row_group_ctr < out_row_groups_avail) {
207	0	if (*in_row_ctr < in_rows_avail) {
208		/* Do color conversion to fill the conversion buffer. */
209	0	inrows = in_rows_avail - *in_row_ctr;
210	0	numrows = prep->next_buf_stop - prep->next_buf_row;
211	0	numrows = (int) MIN((JDIMENSION) numrows, inrows);
212	0	(cinfo->cconvert->color_convert) (cinfo, input_buf + in_row_ctr,
213	0	prep->color_buf,
214	0	(JDIMENSION) prep->next_buf_row,
215	0	numrows);
216		/* Pad at top of image, if first time through */
217	0	if (prep->rows_to_go == cinfo->image_height) {
218	0	for (ci = 0; ci < cinfo->num_components; ci++) {
219	0	int row;
220	0	for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
221	0	jcopy_sample_rows(prep->color_buf[ci], 0,
222	0	prep->color_buf[ci], -row,
223	0	1, cinfo->image_width);
224	0	}
225	0	}
226	0	}
227	0	*in_row_ctr += numrows;
228	0	prep->next_buf_row += numrows;
229	0	prep->rows_to_go -= numrows;
230	0	} else {
231		/* Return for more data, unless we are at the bottom of the image. */
232	0	if (prep->rows_to_go != 0)
233	0	break;
234		/* When at bottom of image, pad to fill the conversion buffer. */
235	0	if (prep->next_buf_row < prep->next_buf_stop) {
236	0	for (ci = 0; ci < cinfo->num_components; ci++) {
237	0	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
238	0	prep->next_buf_row, prep->next_buf_stop);
239	0	}
240	0	prep->next_buf_row = prep->next_buf_stop;
241	0	}
242	0	}
243		/* If we've gotten enough data, downsample a row group. */
244	0	if (prep->next_buf_row == prep->next_buf_stop) {
245	0	(*cinfo->downsample->downsample) (cinfo,
246	0	prep->color_buf,
247	0	(JDIMENSION) prep->this_row_group,
248	0	output_buf, *out_row_group_ctr);
249	0	(*out_row_group_ctr)++;
250		/* Advance pointers with wraparound as necessary. */
251	0	prep->this_row_group += cinfo->max_v_samp_factor;
252	0	if (prep->this_row_group >= buf_height)
253	0	prep->this_row_group = 0;
254	0	if (prep->next_buf_row >= buf_height)
255	0	prep->next_buf_row = 0;
256	0	prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
257	0	}
258	0	}
259	0	}
260
261
262		/*
263		* Create the wrapped-around downsampling input buffer needed for context mode.
264		*/
265
266		LOCAL(void)
267		create_context_buffer (j_compress_ptr cinfo)
268	0	{
269	0	my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
270	0	int rgroup_height = cinfo->max_v_samp_factor;
271	0	int ci, i;
272	0	jpeg_component_info * compptr;
273	0	JSAMPARRAY true_buffer, fake_buffer;
274
275		/* Grab enough space for fake row pointers for all the components;
276		* we need five row groups' worth of pointers for each component.
277		*/
278	0	fake_buffer = (JSAMPARRAY)
279	0	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
280	0	(cinfo->num_components * 5 * rgroup_height) *
281	0	SIZEOF(JSAMPROW));
282
283	0	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
284	0	ci++, compptr++) {
285		/* Allocate the actual buffer space (3 row groups) for this component.
286		* We make the buffer wide enough to allow the downsampler to edge-expand
287		* horizontally within the buffer, if it so chooses.
288		*/
289	0	true_buffer = (*cinfo->mem->alloc_sarray)
290	0	((j_common_ptr) cinfo, JPOOL_IMAGE,
291	0	(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
292	0	cinfo->max_h_samp_factor) / compptr->h_samp_factor),
293	0	(JDIMENSION) (3 * rgroup_height));
294		/* Copy true buffer row pointers into the middle of the fake row array */
295	0	MEMCOPY(fake_buffer + rgroup_height, true_buffer,
296	0	3 * rgroup_height * SIZEOF(JSAMPROW));
297		/* Fill in the above and below wraparound pointers */
298	0	for (i = 0; i < rgroup_height; i++) {
299	0	fake_buffer[i] = true_buffer[2 * rgroup_height + i];
300	0	fake_buffer[4 * rgroup_height + i] = true_buffer[i];
301	0	}
302	0	prep->color_buf[ci] = fake_buffer + rgroup_height;
303	0	fake_buffer += 5 * rgroup_height; /* point to space for next component */
304	0	}
305	0	}
306
307		#endif /* CONTEXT_ROWS_SUPPORTED */
308
309
310		/*
311		* Initialize preprocessing controller.
312		*/
313
314		GLOBAL(void)
315		jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
316	0	{
317	0	my_prep_ptr prep;
318	0	int ci;
319	0	jpeg_component_info * compptr;
320
321	0	if (need_full_buffer) /* safety check */
322	0	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
323
324	0	prep = (my_prep_ptr)
325	0	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
326	0	SIZEOF(my_prep_controller));
327	0	cinfo->prep = (struct jpeg_c_prep_controller *) prep;
328	0	prep->pub.start_pass = start_pass_prep;
329
330		/* Allocate the color conversion buffer.
331		* We make the buffer wide enough to allow the downsampler to edge-expand
332		* horizontally within the buffer, if it so chooses.
333		*/
334	0	if (cinfo->downsample->need_context_rows) {
335		/* Set up to provide context rows */
336	0	#ifdef CONTEXT_ROWS_SUPPORTED
337	0	prep->pub.pre_process_data = pre_process_context;
338	0	create_context_buffer(cinfo);
339		#else
340		ERREXIT(cinfo, JERR_NOT_COMPILED);
341		#endif
342	0	} else {
343		/* No context, just make it tall enough for one row group */
344	0	prep->pub.pre_process_data = pre_process_data;
345	0	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
346	0	ci++, compptr++) {
347	0	prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
348	0	((j_common_ptr) cinfo, JPOOL_IMAGE,
349	0	(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
350	0	cinfo->max_h_samp_factor) / compptr->h_samp_factor),
351	0	(JDIMENSION) cinfo->max_v_samp_factor);
352	0	}
353	0	}
354	0	}