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/*
* jdmcu.c
*
* Copyright (C) 1991, 1992, 1993, 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 MCU disassembly and IDCT control routines.
* These routines are invoked via the disassemble_MCU, reverse_DCT, and
* disassemble_init/term methods.
*/
#include "jinclude.h"
/*
* Fetch one MCU row from entropy_decode, build coefficient array.
* This version is used for noninterleaved (single-component) scans.
*/
METHODDEF void
disassemble_noninterleaved_MCU (decompress_info_ptr cinfo,
JBLOCKIMAGE image_data)
{
JBLOCKROW MCU_data[1];
long mcuindex;
/* this is pretty easy since there is one component and one block per MCU */
/* Pre-zero the target area to speed up entropy decoder */
/* (we assume wholesale zeroing is faster than retail) */
jzero_far((void FAR *) image_data[0][0],
(size_t) (cinfo->MCUs_per_row * SIZEOF(JBLOCK)));
for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
/* Point to the proper spot in the image array for this MCU */
MCU_data[0] = image_data[0][0] + mcuindex;
/* Fetch the coefficient data */
(*cinfo->methods->entropy_decode) (cinfo, MCU_data);
}
}
/*
* Fetch one MCU row from entropy_decode, build coefficient array.
* This version is used for interleaved (multi-component) scans.
*/
METHODDEF void
disassemble_interleaved_MCU (decompress_info_ptr cinfo,
JBLOCKIMAGE image_data)
{
JBLOCKROW MCU_data[MAX_BLOCKS_IN_MCU];
long mcuindex;
short blkn, ci, xpos, ypos;
jpeg_component_info * compptr;
JBLOCKROW image_ptr;
/* Pre-zero the target area to speed up entropy decoder */
/* (we assume wholesale zeroing is faster than retail) */
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
for (ypos = 0; ypos < compptr->MCU_height; ypos++) {
jzero_far((void FAR *) image_data[ci][ypos],
(size_t) (cinfo->MCUs_per_row * compptr->MCU_width * SIZEOF(JBLOCK)));
}
}
for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
/* Point to the proper spots in the image array for this MCU */
blkn = 0;
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
for (ypos = 0; ypos < compptr->MCU_height; ypos++) {
image_ptr = image_data[ci][ypos] + (mcuindex * compptr->MCU_width);
for (xpos = 0; xpos < compptr->MCU_width; xpos++) {
MCU_data[blkn] = image_ptr;
image_ptr++;
blkn++;
}
}
}
/* Fetch the coefficient data */
(*cinfo->methods->entropy_decode) (cinfo, MCU_data);
}
}
/*
* Perform inverse DCT on each block in an MCU row's worth of data;
* output the results into a sample array starting at row start_row.
* NB: start_row can only be nonzero when dealing with a single-component
* scan; otherwise we'd have to pass different offsets for different
* components, since the heights of interleaved MCU rows can vary.
* But the pipeline controller logic is such that this is not necessary.
*/
METHODDEF void
reverse_DCT (decompress_info_ptr cinfo,
JBLOCKIMAGE coeff_data, JSAMPIMAGE output_data, int start_row)
{
DCTBLOCK block;
JBLOCKROW browptr;
JSAMPARRAY srowptr;
jpeg_component_info * compptr;
long blocksperrow, bi;
short numrows, ri;
short ci;
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
/* don't bother to IDCT an uninteresting component */
if (! compptr->component_needed)
continue;
/* calculate size of an MCU row in this component */
blocksperrow = compptr->downsampled_width / DCTSIZE;
numrows = compptr->MCU_height;
/* iterate through all blocks in MCU row */
for (ri = 0; ri < numrows; ri++) {
browptr = coeff_data[ci][ri];
srowptr = output_data[ci] + (ri * DCTSIZE + start_row);
for (bi = 0; bi < blocksperrow; bi++) {
/* copy the data into a local DCTBLOCK. This allows for change of
* representation (if DCTELEM != JCOEF). On 80x86 machines it also
* brings the data back from FAR storage to NEAR storage.
*/
{ register JCOEFPTR elemptr = browptr[bi];
register DCTELEM *localblkptr = block;
register int elem = DCTSIZE2;
while (--elem >= 0)
*localblkptr++ = (DCTELEM) *elemptr++;
}
j_rev_dct(block); /* perform inverse DCT */
/* Output the data into the sample array.
* Note change from signed to unsigned representation:
* DCT calculation works with values +-CENTERJSAMPLE,
* but sample arrays always hold 0..MAXJSAMPLE.
* We have to do range-limiting because of quantization errors in the
* DCT/IDCT phase. We use the sample_range_limit[] table to do this
* quickly; the CENTERJSAMPLE offset is folded into table indexing.
*/
{ register JSAMPROW elemptr;
register DCTELEM *localblkptr = block;
register JSAMPLE *range_limit = cinfo->sample_range_limit +
CENTERJSAMPLE;
#if DCTSIZE != 8
register int elemc;
#endif
register int elemr;
for (elemr = 0; elemr < DCTSIZE; elemr++) {
elemptr = srowptr[elemr] + (bi * DCTSIZE);
#if DCTSIZE == 8 /* unroll the inner loop */
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
*elemptr++ = range_limit[*localblkptr++];
#else
for (elemc = DCTSIZE; elemc > 0; elemc--) {
*elemptr++ = range_limit[*localblkptr++];
}
#endif
}
}
}
}
}
}
/*
* Initialize for processing a scan.
*/
METHODDEF void
disassemble_init (decompress_info_ptr cinfo)
{
/* no work for now */
}
/*
* Clean up after a scan.
*/
METHODDEF void
disassemble_term (decompress_info_ptr cinfo)
{
/* no work for now */
}
/*
* The method selection routine for MCU disassembly.
*/
GLOBAL void
jseldmcu (decompress_info_ptr cinfo)
{
if (cinfo->comps_in_scan == 1)
cinfo->methods->disassemble_MCU = disassemble_noninterleaved_MCU;
else
cinfo->methods->disassemble_MCU = disassemble_interleaved_MCU;
cinfo->methods->reverse_DCT = reverse_DCT;
cinfo->methods->disassemble_init = disassemble_init;
cinfo->methods->disassemble_term = disassemble_term;
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.