Quelle jcdctmgr.c Sprache: C

/*
* reserved comment block
* DO NOT REMOVE OR ALTER!
*/
/*
* jcdctmgr.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 forward-DCT management logic.
* This code selects a particular DCT implementation to be used,
* and it performs related housekeeping chores including coefficient
* quantization.
*/

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"               /* Private declarations for DCT subsystem */

/* Private subobject for this module */

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

  /* Pointer to the DCT routine actually in use */
  forward_DCT_method_ptr do_dct;

  /* The actual post-DCT divisors --- not identical to the quant table
   * entries, because of scaling (especially for an unnormalized DCT).
   * Each table is given in normal array order.
   */
  DCTELEM * divisors[NUM_QUANT_TBLS];

#ifdef DCT_FLOAT_SUPPORTED
  /* Same as above for the floating-point case. */
  float_DCT_method_ptr do_float_dct;
  FAST_FLOAT * float_divisors[NUM_QUANT_TBLS];
#endif
} my_fdct_controller;

typedef my_fdct_controller * my_fdct_ptr;

/*
* Initialize for a processing pass.
* Verify that all referenced Q-tables are present, and set up
* the divisor table for each one.
* In the current implementation, DCT of all components is done during
* the first pass, even if only some components will be output in the
* first scan.  Hence all components should be examined here.
*/

METHODDEF(void)
start_pass_fdctmgr (j_compress_ptr cinfo)
{
  my_fdct_ptr fdct = (my_fdct_ptr) cinfo->fdct;
  int ci, qtblno, i;
  jpeg_component_info *compptr;
  JQUANT_TBL * qtbl;
  DCTELEM * dtbl;

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    qtblno = compptr->quant_tbl_no;
    /* Make sure specified quantization table is present */
    if (qtblno < 0 || qtblno >= NUM_QUANT_TBLS ||
        cinfo->quant_tbl_ptrs[qtblno] == NULL)
      ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, qtblno);
    qtbl = cinfo->quant_tbl_ptrs[qtblno];
    /* Compute divisors for this quant table */
    /* We may do this more than once for same table, but it's not a big deal */
    switch (cinfo->dct_method) {
#ifdef DCT_ISLOW_SUPPORTED
    case JDCT_ISLOW:
      /* For LL&M IDCT method, divisors are equal to raw quantization
       * coefficients multiplied by 8 (to counteract scaling).
       */
      if (fdct->divisors[qtblno] == NULL) {
        fdct->divisors[qtblno] = (DCTELEM *)
          (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                      DCTSIZE2 * SIZEOF(DCTELEM));
      }
      dtbl = fdct->divisors[qtblno];
      for (i = 0; i < DCTSIZE2; i++) {
        dtbl[i] = ((DCTELEM) qtbl->quantval[i]) << 3;
      }
      break;
#endif
#ifdef DCT_IFAST_SUPPORTED
    case JDCT_IFAST:
      {
        /* For AA&N IDCT method, divisors are equal to quantization
         * coefficients scaled by scalefactor[row]*scalefactor[col], where
         *   scalefactor[0] = 1
         *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
         * We apply a further scale factor of 8.
         */
#define CONST_BITS 14
        static const INT16 aanscales[DCTSIZE2] = {
          /* precomputed values scaled up by 14 bits */
          16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
          22725, 31521, 29692, 26722, 22725, 17855, 12299,  6270,
          21407, 29692, 27969, 25172, 21407, 16819, 11585,  5906,
          19266, 26722, 25172, 22654, 19266, 15137, 10426,  5315,
          16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
          12873, 17855, 16819, 15137, 12873, 10114,  6967,  3552,
           8867, 12299, 11585, 10426,  8867,  6967,  4799,  2446,
           4520,  6270,  5906,  5315,  4520,  3552,  2446,  1247
        };
        SHIFT_TEMPS

        if (fdct->divisors[qtblno] == NULL) {
          fdct->divisors[qtblno] = (DCTELEM *)
            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                        DCTSIZE2 * SIZEOF(DCTELEM));
        }
        dtbl = fdct->divisors[qtblno];
        for (i = 0; i < DCTSIZE2; i++) {
          dtbl[i] = (DCTELEM)
            DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
                                  (INT32) aanscales[i]),
                    CONST_BITS-3);
        }
      }
      break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
    case JDCT_FLOAT:
      {
        /* For float AA&N IDCT method, divisors are equal to quantization
         * coefficients scaled by scalefactor[row]*scalefactor[col], where
         *   scalefactor[0] = 1
         *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
         * We apply a further scale factor of 8.
         * What's actually stored is 1/divisor so that the inner loop can
         * use a multiplication rather than a division.
         */
        FAST_FLOAT * fdtbl;
        int row, col;
        static const double aanscalefactor[DCTSIZE] = {
          1.0, 1.387039845, 1.306562965, 1.175875602,
          1.0, 0.785694958, 0.541196100, 0.275899379
        };

        if (fdct->float_divisors[qtblno] == NULL) {
          fdct->float_divisors[qtblno] = (FAST_FLOAT *)
            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                        DCTSIZE2 * SIZEOF(FAST_FLOAT));
        }
        fdtbl = fdct->float_divisors[qtblno];
        i = 0;
        for (row = 0; row < DCTSIZE; row++) {
          for (col = 0; col < DCTSIZE; col++) {
            fdtbl[i] = (FAST_FLOAT)
              (1.0 / (((double) qtbl->quantval[i] *
                       aanscalefactor[row] * aanscalefactor[col] * 8.0)));
            i++;
          }
        }
      }
      break;
#endif
    default:
      ERREXIT(cinfo, JERR_NOT_COMPILED);
      break;
    }
  }
}

/*
* Perform forward DCT on one or more blocks of a component.
*
* The input samples are taken from the sample_data[] array starting at
* position start_row/start_col, and moving to the right for any additional
* blocks. The quantized coefficients are returned in coef_blocks[].
*/

METHODDEF(void)
forward_DCT (j_compress_ptr cinfo, jpeg_component_info * compptr,
             JSAMPARRAY sample_data, JBLOCKROW coef_blocks,
             JDIMENSION start_row, JDIMENSION start_col,
             JDIMENSION num_blocks)
/* This version is used for integer DCT implementations. */
{
  /* This routine is heavily used, so it's worth coding it tightly. */
  my_fdct_ptr fdct = (my_fdct_ptr) cinfo->fdct;
  forward_DCT_method_ptr do_dct = fdct->do_dct;
  DCTELEM * divisors = fdct->divisors[compptr->quant_tbl_no];
  DCTELEM workspace[DCTSIZE2];  /* work area for FDCT subroutine */
  JDIMENSION bi;

  sample_data += start_row;     /* fold in the vertical offset once */

  for (bi = 0; bi < num_blocks; bi++, start_col += DCTSIZE) {
    /* Load data into workspace, applying unsigned->signed conversion */
    { register DCTELEM *workspaceptr;
      register JSAMPROW elemptr;
      register int elemr;

      workspaceptr = workspace;
      for (elemr = 0; elemr < DCTSIZE; elemr++) {
        elemptr = sample_data[elemr] + start_col;
#if DCTSIZE == 8                /* unroll the inner loop */
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
        *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
#else
        { register int elemc;
          for (elemc = DCTSIZE; elemc > 0; elemc--) {
            *workspaceptr++ = GETJSAMPLE(*elemptr++) - CENTERJSAMPLE;
          }
        }
#endif
      }
    }

    /* Perform the DCT */
    (*do_dct) (workspace);

    /* Quantize/descale the coefficients, and store into coef_blocks[] */
    { register DCTELEM temp, qval;
      register int i;
      register JCOEFPTR output_ptr = coef_blocks[bi];

      for (i = 0; i < DCTSIZE2; i++) {
        qval = divisors[i];
        temp = workspace[i];
        /* Divide the coefficient value by qval, ensuring proper rounding.
         * Since C does not specify the direction of rounding for negative
         * quotients, we have to force the dividend positive for portability.
         *
         * In most files, at least half of the output values will be zero
         * (at default quantization settings, more like three-quarters...)
         * so we should ensure that this case is fast.  On many machines,
         * a comparison is enough cheaper than a divide to make a special test
         * a win.  Since both inputs will be nonnegative, we need only test
         * for a < b to discover whether a/b is 0.
         * If your machine's division is fast enough, define FAST_DIVIDE.
         */
#ifdef FAST_DIVIDE
#define DIVIDE_BY(a,b)  a /= b
#else
#define DIVIDE_BY(a,b)  if (a >= b) a /= b; else a = 0
#endif
        if (temp < 0) {
          temp = -temp;
          temp += qval>>1;      /* for rounding */
          DIVIDE_BY(temp, qval);
          temp = -temp;
        } else {
          temp += qval>>1;      /* for rounding */
          DIVIDE_BY(temp, qval);
        }
        output_ptr[i] = (JCOEF) temp;
      }
    }
  }
}

#ifdef DCT_FLOAT_SUPPORTED

METHODDEF(void)
forward_DCT_float (j_compress_ptr cinfo, jpeg_component_info * compptr,
                   JSAMPARRAY sample_data, JBLOCKROW coef_blocks,
                   JDIMENSION start_row, JDIMENSION start_col,
                   JDIMENSION num_blocks)
/* This version is used for floating-point DCT implementations. */
{
  /* This routine is heavily used, so it's worth coding it tightly. */
  my_fdct_ptr fdct = (my_fdct_ptr) cinfo->fdct;
  float_DCT_method_ptr do_dct = fdct->do_float_dct;
  FAST_FLOAT * divisors = fdct->float_divisors[compptr->quant_tbl_no];
  FAST_FLOAT workspace[DCTSIZE2]; /* work area for FDCT subroutine */
  JDIMENSION bi;

  sample_data += start_row;     /* fold in the vertical offset once */

  for (bi = 0; bi < num_blocks; bi++, start_col += DCTSIZE) {
    /* Load data into workspace, applying unsigned->signed conversion */
    { register FAST_FLOAT *workspaceptr;
      register JSAMPROW elemptr;
      register int elemr;

      workspaceptr = workspace;
      for (elemr = 0; elemr < DCTSIZE; elemr++) {
        elemptr = sample_data[elemr] + start_col;
#if DCTSIZE == 8                /* unroll the inner loop */
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
        *workspaceptr++ = (FAST_FLOAT)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
#else
        { register int elemc;
          for (elemc = DCTSIZE; elemc > 0; elemc--) {
            *workspaceptr++ = (FAST_FLOAT)
              (GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
          }
        }
#endif
      }
    }

    /* Perform the DCT */
    (*do_dct) (workspace);

    /* Quantize/descale the coefficients, and store into coef_blocks[] */
    { register FAST_FLOAT temp;
      register int i;
      register JCOEFPTR output_ptr = coef_blocks[bi];

      for (i = 0; i < DCTSIZE2; i++) {
        /* Apply the quantization and scaling factor */
        temp = workspace[i] * divisors[i];
        /* Round to nearest integer.
         * Since C does not specify the direction of rounding for negative
         * quotients, we have to force the dividend positive for portability.
         * The maximum coefficient size is +-16K (for 12-bit data), so this
         * code should work for either 16-bit or 32-bit ints.
         */
        output_ptr[i] = (JCOEF) ((int) (temp + (FAST_FLOAT) 16384.5) - 16384);
      }
    }
  }
}

#endif /* DCT_FLOAT_SUPPORTED */

/*
* Initialize FDCT manager.
*/

GLOBAL(void)
jinit_forward_dct (j_compress_ptr cinfo)
{
  my_fdct_ptr fdct;
  int i;

  fdct = (my_fdct_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                SIZEOF(my_fdct_controller));
  cinfo->fdct = (struct jpeg_forward_dct *) fdct;
  fdct->pub.start_pass = start_pass_fdctmgr;

  switch (cinfo->dct_method) {
#ifdef DCT_ISLOW_SUPPORTED
  case JDCT_ISLOW:
    fdct->pub.forward_DCT = forward_DCT;
    fdct->do_dct = jpeg_fdct_islow;
    break;
#endif
#ifdef DCT_IFAST_SUPPORTED
  case JDCT_IFAST:
    fdct->pub.forward_DCT = forward_DCT;
    fdct->do_dct = jpeg_fdct_ifast;
    break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
  case JDCT_FLOAT:
    fdct->pub.forward_DCT = forward_DCT_float;
    fdct->do_float_dct = jpeg_fdct_float;
    break;
#endif
  default:
    ERREXIT(cinfo, JERR_NOT_COMPILED);
    break;
  }

  /* Mark divisor tables unallocated */
  for (i = 0; i < NUM_QUANT_TBLS; i++) {
    fdct->divisors[i] = NULL;
#ifdef DCT_FLOAT_SUPPORTED
    fdct->float_divisors[i] = NULL;
#endif
  }
}

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