The Independent JPEG Group's JPEG software v5
diff --git a/jccoefct.c b/jccoefct.c
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+/*
+ * jccoefct.c
+ *
+ * Copyright (C) 1994, 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 coefficient buffer controller for compression.
+ * This controller is the top level of the JPEG compressor proper.
+ * The coefficient buffer lies between forward-DCT and entropy encoding steps.
+ */
+
+#define JPEG_INTERNALS
+#include "jinclude.h"
+#include "jpeglib.h"
+
+
+/* We use a full-image coefficient buffer when doing Huffman optimization,
+ * and also for writing multiple-scan JPEG files. In all cases, the DCT
+ * step is run during the first pass, and subsequent passes need only read
+ * the buffered coefficients.
+ */
+#ifdef ENTROPY_OPT_SUPPORTED
+#define FULL_COEF_BUFFER_SUPPORTED
+#else
+#ifdef C_MULTISCAN_FILES_SUPPORTED
+#define FULL_COEF_BUFFER_SUPPORTED
+#endif
+#endif
+
+
+/* Private buffer controller object */
+
+typedef struct {
+ struct jpeg_c_coef_controller pub; /* public fields */
+
+ JDIMENSION MCU_row_num; /* keep track of MCU row # within image */
+
+ /* For single-pass compression, it's sufficient to buffer just one MCU
+ * (although this may prove a bit slow in practice). We allocate a
+ * workspace of MAX_BLOCKS_IN_MCU coefficient blocks, and reuse it for each
+ * MCU constructed and sent. (On 80x86, the workspace is FAR even though
+ * it's not really very big; this is to keep the module interfaces unchanged
+ * when a large coefficient buffer is necessary.)
+ * In multi-pass modes, this array points to the current MCU's blocks
+ * within the virtual arrays.
+ */
+ JBLOCKROW MCU_buffer[MAX_BLOCKS_IN_MCU];
+
+ /* In multi-pass modes, we need a virtual block array for each component. */
+ jvirt_barray_ptr whole_image[MAX_COMPONENTS];
+} my_coef_controller;
+
+typedef my_coef_controller * my_coef_ptr;
+
+
+/* Forward declarations */
+METHODDEF void compress_data
+ JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
+#ifdef FULL_COEF_BUFFER_SUPPORTED
+METHODDEF void compress_first_pass
+ JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
+METHODDEF void compress_output
+ JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
+#endif
+
+
+/*
+ * Initialize for a processing pass.
+ */
+
+METHODDEF void
+start_pass_coef (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
+{
+ my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
+
+ coef->MCU_row_num = 0;
+
+ switch (pass_mode) {
+ case JBUF_PASS_THRU:
+ if (coef->whole_image[0] != NULL)
+ ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
+ coef->pub.compress_data = compress_data;
+ break;
+#ifdef FULL_COEF_BUFFER_SUPPORTED
+ case JBUF_SAVE_AND_PASS:
+ if (coef->whole_image[0] == NULL)
+ ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
+ coef->pub.compress_data = compress_first_pass;
+ break;
+ case JBUF_CRANK_DEST:
+ if (coef->whole_image[0] == NULL)
+ ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
+ coef->pub.compress_data = compress_output;
+ break;
+#endif
+ default:
+ ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
+ break;
+ }
+}
+
+
+/*
+ * Process some data in the single-pass case.
+ * Up to one MCU row is processed (less if suspension is forced).
+ *
+ * NB: input_buf contains a plane for each component in image.
+ * For single pass, this is the same as the components in the scan.
+ */
+
+METHODDEF void
+compress_data (j_compress_ptr cinfo,
+ JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr)
+{
+ my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
+ JDIMENSION MCU_col_num; /* index of current MCU within row */
+ JDIMENSION last_MCU_col = cinfo->MCUs_per_row - 1;
+ JDIMENSION last_MCU_row = cinfo->MCU_rows_in_scan - 1;
+ int blkn, bi, ci, yindex, blockcnt;
+ JDIMENSION ypos, xpos;
+ jpeg_component_info *compptr;
+
+ /* Loop to write as much as one whole MCU row */
+
+ for (MCU_col_num = *in_mcu_ctr; MCU_col_num <= last_MCU_col; MCU_col_num++) {
+ /* Determine where data comes from in input_buf and do the DCT thing.
+ * Each call on forward_DCT processes a horizontal row of DCT blocks
+ * as wide as an MCU; we rely on having allocated the MCU_buffer[] blocks
+ * sequentially. Dummy blocks at the right or bottom edge are filled in
+ * specially. The data in them does not matter for image reconstruction,
+ * so we fill them with values that will encode to the smallest amount of
+ * data, viz: all zeroes in the AC entries, DC entries equal to previous
+ * block's DC value. (Thanks to Thomas Kinsman for this idea.)
+ */
+ blkn = 0;
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ blockcnt = (MCU_col_num < last_MCU_col) ? compptr->MCU_width
+ : compptr->last_col_width;
+ xpos = MCU_col_num * compptr->MCU_sample_width;
+ ypos = 0;
+ for (yindex = 0; yindex < compptr->MCU_height; yindex++) {
+ if (coef->MCU_row_num < last_MCU_row ||
+ yindex < compptr->last_row_height) {
+ (*cinfo->fdct->forward_DCT) (cinfo, compptr,
+ input_buf[ci], coef->MCU_buffer[blkn],
+ ypos, xpos, (JDIMENSION) blockcnt);
+ if (blockcnt < compptr->MCU_width) {
+ /* Create some dummy blocks at the right edge of the image. */
+ jzero_far((void FAR *) coef->MCU_buffer[blkn + blockcnt],
+ (compptr->MCU_width - blockcnt) * SIZEOF(JBLOCK));
+ for (bi = blockcnt; bi < compptr->MCU_width; bi++) {
+ coef->MCU_buffer[blkn+bi][0][0] = coef->MCU_buffer[blkn+bi-1][0][0];
+ }
+ }
+ } else {
+ /* Create a whole row of dummy blocks at the bottom of the image. */
+ jzero_far((void FAR *) coef->MCU_buffer[blkn],
+ compptr->MCU_width * SIZEOF(JBLOCK));
+ for (bi = 0; bi < compptr->MCU_width; bi++) {
+ coef->MCU_buffer[blkn+bi][0][0] = coef->MCU_buffer[blkn-1][0][0];
+ }
+ }
+ blkn += compptr->MCU_width;
+ ypos += DCTSIZE;
+ }
+ }
+ /* Try to write the MCU. In event of a suspension failure, we will
+ * re-DCT the MCU on restart (a bit inefficient, could be fixed...)
+ */
+ if (! (*cinfo->entropy->encode_mcu) (cinfo, coef->MCU_buffer))
+ break; /* suspension forced; exit loop */
+ }
+ if (MCU_col_num > last_MCU_col)
+ coef->MCU_row_num++; /* advance if we finished the row */
+ *in_mcu_ctr = MCU_col_num;
+}
+
+
+#ifdef FULL_COEF_BUFFER_SUPPORTED
+
+/*
+ * Process some data in the first pass of a multi-pass case.
+ * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
+ * per call, ie, v_samp_factor block rows for each component in the image.
+ * This amount of data is read from the source buffer, DCT'd and quantized,
+ * and saved into the virtual arrays. We also generate suitable dummy blocks
+ * as needed at the right and lower edges. (The dummy blocks are constructed
+ * in the virtual arrays, which have been padded appropriately.) This makes
+ * it possible for subsequent passes not to worry about real vs. dummy blocks.
+ *
+ * We must also emit the data to the entropy encoder. This is conveniently
+ * done by calling compress_output() after we've loaded the current strip
+ * of the virtual arrays.
+ *
+ * NB: input_buf contains a plane for each component in image. All
+ * components are DCT'd and loaded into the virtual arrays in this pass.
+ * However, it may be that only a subset of the components are emitted to
+ * the entropy encoder during this first pass; be careful about looking
+ * at the scan-dependent variables (MCU dimensions, etc).
+ */
+
+METHODDEF void
+compress_first_pass (j_compress_ptr cinfo,
+ JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr)
+{
+ my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
+ JDIMENSION last_MCU_row = cinfo->total_iMCU_rows - 1;
+ JDIMENSION blocks_across, MCUs_across, MCUindex;
+ int bi, ci, h_samp_factor, block_row, block_rows, ndummy;
+ JCOEF lastDC;
+ jpeg_component_info *compptr;
+ JBLOCKARRAY buffer;
+ JBLOCKROW thisblockrow, lastblockrow;
+
+ for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
+ ci++, compptr++) {
+ /* Align the virtual buffer for this component. */
+ buffer = (*cinfo->mem->access_virt_barray)
+ ((j_common_ptr) cinfo, coef->whole_image[ci],
+ coef->MCU_row_num * compptr->v_samp_factor, TRUE);
+ /* Count non-dummy DCT block rows in this iMCU row. */
+ if (coef->MCU_row_num < last_MCU_row)
+ block_rows = compptr->v_samp_factor;
+ else {
+ block_rows = (int) (compptr->height_in_blocks % compptr->v_samp_factor);
+ if (block_rows == 0) block_rows = compptr->v_samp_factor;
+ }
+ blocks_across = compptr->width_in_blocks;
+ h_samp_factor = compptr->h_samp_factor;
+ /* Count number of dummy blocks to be added at the right margin. */
+ ndummy = (int) (blocks_across % h_samp_factor);
+ if (ndummy > 0)
+ ndummy = h_samp_factor - ndummy;
+ /* Perform DCT for all non-dummy blocks in this iMCU row. Each call
+ * on forward_DCT processes a complete horizontal row of DCT blocks.
+ */
+ for (block_row = 0; block_row < block_rows; block_row++) {
+ thisblockrow = buffer[block_row];
+ (*cinfo->fdct->forward_DCT) (cinfo, compptr,
+ input_buf[ci], thisblockrow,
+ (JDIMENSION) (block_row * DCTSIZE),
+ (JDIMENSION) 0, blocks_across);
+ if (ndummy > 0) {
+ /* Create dummy blocks at the right edge of the image. */
+ thisblockrow += blocks_across; /* => first dummy block */
+ jzero_far((void FAR *) thisblockrow, ndummy * SIZEOF(JBLOCK));
+ lastDC = thisblockrow[-1][0];
+ for (bi = 0; bi < ndummy; bi++) {
+ thisblockrow[bi][0] = lastDC;
+ }
+ }
+ }
+ /* If at end of image, create dummy block rows as needed.
+ * The tricky part here is that within each MCU, we want the DC values
+ * of the dummy blocks to match the last real block's DC value.
+ * This squeezes a few more bytes out of the resulting file...
+ */
+ if (coef->MCU_row_num == last_MCU_row) {
+ blocks_across += ndummy; /* include lower right corner */
+ MCUs_across = blocks_across / h_samp_factor;
+ for (block_row = block_rows; block_row < compptr->v_samp_factor;
+ block_row++) {
+ thisblockrow = buffer[block_row];
+ lastblockrow = buffer[block_row-1];
+ jzero_far((void FAR *) thisblockrow,
+ (size_t) (blocks_across * SIZEOF(JBLOCK)));
+ for (MCUindex = 0; MCUindex < MCUs_across; MCUindex++) {
+ lastDC = lastblockrow[h_samp_factor-1][0];
+ for (bi = 0; bi < h_samp_factor; bi++) {
+ thisblockrow[bi][0] = lastDC;
+ }
+ thisblockrow += h_samp_factor; /* advance to next MCU in row */
+ lastblockrow += h_samp_factor;
+ }
+ }
+ }
+ }
+ /* NB: compress_output will increment MCU_row_num */
+
+ /* Emit data to the entropy encoder, sharing code with subsequent passes */
+ compress_output(cinfo, input_buf, in_mcu_ctr);
+}
+
+
+/*
+ * Process some data in subsequent passes of a multi-pass case.
+ * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
+ * per call, ie, v_samp_factor block rows for each component in the scan.
+ * The data is obtained from the virtual arrays and fed to the entropy coder.
+ *
+ * Note that output suspension is not supported during multi-pass operation,
+ * so the complete MCU row will always be emitted to the entropy encoder
+ * before returning.
+ *
+ * NB: input_buf is ignored; it is likely to be a NULL pointer.
+ */
+
+METHODDEF void
+compress_output (j_compress_ptr cinfo,
+ JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr)
+{
+ my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
+ JDIMENSION MCU_col_num; /* index of current MCU within row */
+ int blkn, ci, xindex, yindex, yoffset, num_MCU_rows;
+ JDIMENSION remaining_rows, start_col;
+ JBLOCKARRAY buffer[MAX_COMPS_IN_SCAN];
+ JBLOCKROW buffer_ptr;
+ jpeg_component_info *compptr;
+
+ /* Align the virtual buffers for the components used in this scan.
+ * NB: during first pass, this is safe only because the buffers will
+ * already be aligned properly, so jmemmgr.c won't need to do any I/O.
+ */
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ buffer[ci] = (*cinfo->mem->access_virt_barray)
+ ((j_common_ptr) cinfo, coef->whole_image[compptr->component_index],
+ coef->MCU_row_num * compptr->v_samp_factor, FALSE);
+ }
+
+ /* In an interleaved scan, we process exactly one MCU row.
+ * In a noninterleaved scan, we need to process v_samp_factor MCU rows,
+ * each of which contains a single block row.
+ */
+ if (cinfo->comps_in_scan == 1) {
+ compptr = cinfo->cur_comp_info[0];
+ num_MCU_rows = compptr->v_samp_factor;
+ /* but watch out for the bottom of the image */
+ remaining_rows = cinfo->MCU_rows_in_scan -
+ coef->MCU_row_num * compptr->v_samp_factor;
+ if (remaining_rows < (JDIMENSION) num_MCU_rows)
+ num_MCU_rows = (int) remaining_rows;
+ } else {
+ num_MCU_rows = 1;
+ }
+
+ /* Loop to process one whole iMCU row */
+ for (yoffset = 0; yoffset < num_MCU_rows; yoffset++) {
+ for (MCU_col_num = 0; MCU_col_num < cinfo->MCUs_per_row; MCU_col_num++) {
+ /* Construct list of pointers to DCT blocks belonging to this MCU */
+ blkn = 0; /* index of current DCT block within MCU */
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ start_col = MCU_col_num * compptr->MCU_width;
+ for (yindex = 0; yindex < compptr->MCU_height; yindex++) {
+ buffer_ptr = buffer[ci][yindex+yoffset] + start_col;
+ for (xindex = 0; xindex < compptr->MCU_width; xindex++) {
+ coef->MCU_buffer[blkn++] = buffer_ptr++;
+ }
+ }
+ }
+ /* Try to write the MCU. */
+ if (! (*cinfo->entropy->encode_mcu) (cinfo, coef->MCU_buffer)) {
+ ERREXIT(cinfo, JERR_CANT_SUSPEND); /* not supported */
+ }
+ }
+ }
+
+ coef->MCU_row_num++; /* advance to next iMCU row */
+ *in_mcu_ctr = cinfo->MCUs_per_row;
+}
+
+#endif /* FULL_COEF_BUFFER_SUPPORTED */
+
+
+/*
+ * Initialize coefficient buffer controller.
+ */
+
+GLOBAL void
+jinit_c_coef_controller (j_compress_ptr cinfo, boolean need_full_buffer)
+{
+ my_coef_ptr coef;
+ int ci, i;
+ jpeg_component_info *compptr;
+ JBLOCKROW buffer;
+
+ coef = (my_coef_ptr)
+ (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
+ SIZEOF(my_coef_controller));
+ cinfo->coef = (struct jpeg_c_coef_controller *) coef;
+ coef->pub.start_pass = start_pass_coef;
+
+ /* Create the coefficient buffer. */
+ if (need_full_buffer) {
+#ifdef FULL_COEF_BUFFER_SUPPORTED
+ /* Allocate a full-image virtual array for each component, */
+ /* padded to a multiple of samp_factor DCT blocks in each direction. */
+ /* Note memmgr implicitly pads the vertical direction. */
+ for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
+ ci++, compptr++) {
+ coef->whole_image[ci] = (*cinfo->mem->request_virt_barray)
+ ((j_common_ptr) cinfo, JPOOL_IMAGE,
+ (JDIMENSION) jround_up((long) compptr->width_in_blocks,
+ (long) compptr->h_samp_factor),
+ compptr->height_in_blocks,
+ (JDIMENSION) compptr->v_samp_factor);
+ }
+#else
+ ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
+#endif
+ } else {
+ /* We only need a single-MCU buffer. */
+ buffer = (JBLOCKROW)
+ (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,
+ MAX_BLOCKS_IN_MCU * SIZEOF(JBLOCK));
+ for (i = 0; i < MAX_BLOCKS_IN_MCU; i++) {
+ coef->MCU_buffer[i] = buffer + i;
+ }
+ coef->whole_image[0] = NULL; /* flag for no virtual arrays */
+ }
+}