jdmcu.c

/*
 * jdmcu.c
 *
 * Copyright (C) 1991, 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 routines and quantization descaling.
 * These routines are invoked via the disassemble_MCU and
 * disassemble_init/term methods.
 */

#include "jinclude.h"


/*
 * Quantization descaling and zigzag reordering
 */


/* ZAG[i] is the natural-order position of the i'th element of zigzag order. */

static const short ZAG[DCTSIZE2] = {
  0,  1,  8, 16,  9,  2,  3, 10,
 17, 24, 32, 25, 18, 11,  4,  5,
 12, 19, 26, 33, 40, 48, 41, 34,
 27, 20, 13,  6,  7, 14, 21, 28,
 35, 42, 49, 56, 57, 50, 43, 36,
 29, 22, 15, 23, 30, 37, 44, 51,
 58, 59, 52, 45, 38, 31, 39, 46,
 53, 60, 61, 54, 47, 55, 62, 63
};


LOCAL void
qdescale_zig (JBLOCK input, JBLOCKROW outputptr, QUANT_TBL_PTR quanttbl)
{
  short i;

  for (i = 0; i < DCTSIZE2; i++) {
    (*outputptr)[ZAG[i]] = (*input++) * (*quanttbl++);
  }
}



/*
 * 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)
{
  JBLOCK MCU_data[1];
  long mcuindex;
  jpeg_component_info * compptr;
  QUANT_TBL_PTR quant_ptr;

  /* this is pretty easy since there is one component and one block per MCU */
  compptr = cinfo->cur_comp_info[0];
  quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
  for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
    /* Fetch the coefficient data */
    (*cinfo->methods->entropy_decode) (cinfo, MCU_data);
    /* Descale, reorder, and distribute it into the image array */
    qdescale_zig(MCU_data[0], image_data[0][0] + mcuindex, quant_ptr);
  }
}


/*
 * 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)
{
  JBLOCK MCU_data[MAX_BLOCKS_IN_MCU];
  long mcuindex;
  short blkn, ci, xpos, ypos;
  jpeg_component_info * compptr;
  QUANT_TBL_PTR quant_ptr;
  JBLOCKROW image_ptr;

  for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
    /* Fetch the coefficient data */
    (*cinfo->methods->entropy_decode) (cinfo, MCU_data);
    /* Descale, reorder, and distribute it into the image array */
    blkn = 0;
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
      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++) {
	  qdescale_zig(MCU_data[blkn], image_ptr, quant_ptr);
	  image_ptr++;
	  blkn++;
	}
      }
    }
  }
}


/*
 * 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->disassemble_init = disassemble_init;
  cinfo->methods->disassemble_term = disassemble_term;
}