jcdctmgr.c

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/*
 * jcdctmgr.c
 *
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * Modified 2003-2025 by Guido Vollbeding.
 * 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[MAX_COMPONENTS];
 
#ifdef DCT_FLOAT_SUPPORTED
  /* Same as above for the floating-point case. */
  float_DCT_method_ptr do_float_dct[MAX_COMPONENTS];
#endif
} my_fdct_controller;
 
typedef my_fdct_controller * my_fdct_ptr;
 
 
/* The allocated post-DCT divisor tables -- big enough for any
 * supported variant and not identical to the quant table entries,
 * because of scaling (especially for an unnormalized DCT) --
 * are pointed to by dct_table in the per-component comp_info
 * structures.  Each table is given in normal array order.
 */
 
typedef union {
  DCTELEM int_array[DCTSIZE2];
#ifdef DCT_FLOAT_SUPPORTED
  FAST_FLOAT float_array[DCTSIZE2];
#endif
} divisor_table;
 
 
/*
 * 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_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_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[compptr->component_index];
  DCTELEM * divisors = (DCTELEM *) compptr->dct_table;
  DCTELEM workspace[DCTSIZE2];  /* work area for FDCT subroutine */
  JDIMENSION bi;
 
  for (bi = 0; bi < num_blocks; bi++, start_col += compptr->DCT_h_scaled_size) {
    /* Perform the DCT */
    (*do_dct) (workspace, sample_data, start_col);
 
    /* 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_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[compptr->component_index];
  FAST_FLOAT * divisors = (FAST_FLOAT *) compptr->dct_table;
  FAST_FLOAT workspace[DCTSIZE2]; /* work area for FDCT subroutine */
  JDIMENSION bi;
 
  for (bi = 0; bi < num_blocks; bi++, start_col += compptr->DCT_h_scaled_size) {
    /* Perform the DCT */
    (*do_dct) (workspace, sample_data, start_col);
 
    /* 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 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;
  J_DCT_METHOD method = JDCT_DEFAULT;
  JQUANT_TBL * qtbl;
  DCTELEM * dtbl;
 
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    /* Select the proper DCT routine for this component's scaling */
    switch ((compptr->DCT_h_scaled_size << 8) + compptr->DCT_v_scaled_size) {
#ifdef DCT_SCALING_SUPPORTED
/*
 * The current scaled-DCT routines require ISLOW-style divisor tables,
 * so be sure to compile that code if either ISLOW or SCALING is requested.
 */
#ifndef PROVIDE_ISLOW_TABLES
#define PROVIDE_ISLOW_TABLES
#endif
    case ((1 << 8) + 1):
      fdct->do_dct[ci] = jpeg_fdct_1x1;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((2 << 8) + 2):
      fdct->do_dct[ci] = jpeg_fdct_2x2;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((3 << 8) + 3):
      fdct->do_dct[ci] = jpeg_fdct_3x3;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((4 << 8) + 4):
      fdct->do_dct[ci] = jpeg_fdct_4x4;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((5 << 8) + 5):
      fdct->do_dct[ci] = jpeg_fdct_5x5;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((6 << 8) + 6):
      fdct->do_dct[ci] = jpeg_fdct_6x6;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((7 << 8) + 7):
      fdct->do_dct[ci] = jpeg_fdct_7x7;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((9 << 8) + 9):
      fdct->do_dct[ci] = jpeg_fdct_9x9;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((10 << 8) + 10):
      fdct->do_dct[ci] = jpeg_fdct_10x10;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((11 << 8) + 11):
      fdct->do_dct[ci] = jpeg_fdct_11x11;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((12 << 8) + 12):
      fdct->do_dct[ci] = jpeg_fdct_12x12;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((13 << 8) + 13):
      fdct->do_dct[ci] = jpeg_fdct_13x13;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((14 << 8) + 14):
      fdct->do_dct[ci] = jpeg_fdct_14x14;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((15 << 8) + 15):
      fdct->do_dct[ci] = jpeg_fdct_15x15;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((16 << 8) + 16):
      fdct->do_dct[ci] = jpeg_fdct_16x16;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((16 << 8) + 8):
      fdct->do_dct[ci] = jpeg_fdct_16x8;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((14 << 8) + 7):
      fdct->do_dct[ci] = jpeg_fdct_14x7;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((12 << 8) + 6):
      fdct->do_dct[ci] = jpeg_fdct_12x6;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((10 << 8) + 5):
      fdct->do_dct[ci] = jpeg_fdct_10x5;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((8 << 8) + 4):
      fdct->do_dct[ci] = jpeg_fdct_8x4;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((6 << 8) + 3):
      fdct->do_dct[ci] = jpeg_fdct_6x3;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((4 << 8) + 2):
      fdct->do_dct[ci] = jpeg_fdct_4x2;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((2 << 8) + 1):
      fdct->do_dct[ci] = jpeg_fdct_2x1;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((8 << 8) + 16):
      fdct->do_dct[ci] = jpeg_fdct_8x16;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((7 << 8) + 14):
      fdct->do_dct[ci] = jpeg_fdct_7x14;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((6 << 8) + 12):
      fdct->do_dct[ci] = jpeg_fdct_6x12;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((5 << 8) + 10):
      fdct->do_dct[ci] = jpeg_fdct_5x10;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((4 << 8) + 8):
      fdct->do_dct[ci] = jpeg_fdct_4x8;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((3 << 8) + 6):
      fdct->do_dct[ci] = jpeg_fdct_3x6;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((2 << 8) + 4):
      fdct->do_dct[ci] = jpeg_fdct_2x4;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
    case ((1 << 8) + 2):
      fdct->do_dct[ci] = jpeg_fdct_1x2;
      method = JDCT_ISLOW;  /* jfdctint uses islow-style table */
      break;
#endif
    case ((DCTSIZE << 8) + DCTSIZE):
      switch (cinfo->dct_method) {
#ifdef DCT_ISLOW_SUPPORTED
      case JDCT_ISLOW:
#ifndef PROVIDE_ISLOW_TABLES
#define PROVIDE_ISLOW_TABLES
#endif
    fdct->do_dct[ci] = jpeg_fdct_islow;
    method = JDCT_ISLOW;
    break;
#endif
#ifdef DCT_IFAST_SUPPORTED
      case JDCT_IFAST:
#if BITS_IN_JSAMPLE < JPEG_DATA_PRECISION || \
    BITS_IN_JSAMPLE > JPEG_DATA_PRECISION + 8
    /*
     * Adjustment of divisor tables in JDCT_IFAST
     * below doesn't work well in this condition.
     * Use JDCT_ISLOW instead.
     */
#ifndef PROVIDE_ISLOW_TABLES
#define PROVIDE_ISLOW_TABLES
#endif
    fdct->do_dct[ci] = jpeg_fdct_islow;
    method = JDCT_ISLOW;
#else
#ifndef PROVIDE_IFAST_TABLES
#define PROVIDE_IFAST_TABLES
#endif
    fdct->do_dct[ci] = jpeg_fdct_ifast;
    method = JDCT_IFAST;
#endif
    break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
      case JDCT_FLOAT:
    fdct->do_float_dct[ci] = jpeg_fdct_float;
    method = JDCT_FLOAT;
    break;
#endif
      default:
    ERREXIT(cinfo, JERR_NOT_COMPILED);
      }
      break;
    default:
      ERREXIT2(cinfo, JERR_BAD_DCTSIZE,
           compptr->DCT_h_scaled_size, compptr->DCT_v_scaled_size);
    }
    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];
    /* Create divisor table from quant table */
    switch (method) {
#ifdef PROVIDE_ISLOW_TABLES
    case JDCT_ISLOW:
      /* For LL&M FDCT method, divisors are equal to raw quantization
       * coefficients multiplied by 8 (to counteract scaling).
       */
      dtbl = (DCTELEM *) compptr->dct_table;
      for (i = 0; i < DCTSIZE2; i++) {
    dtbl[i] =
      ((DCTELEM) qtbl->quantval[i]) << (compptr->component_needed ? 4 : 3);
      }
      fdct->pub.forward_DCT[ci] = forward_DCT;
      break;
#endif
#ifdef PROVIDE_IFAST_TABLES
    case JDCT_IFAST:
      {
    /* For AA&N FDCT 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
     * with adjustment if necessary.
     */
#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
 
    dtbl = (DCTELEM *) compptr->dct_table;
    if (compptr->component_needed) {
      for (i = 0; i < DCTSIZE2; i++) {
        dtbl[i] = (DCTELEM)
          DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
                    (INT32) aanscales[i]),
              CONST_BITS+JPEG_DATA_PRECISION-BITS_IN_JSAMPLE-4);
      }
    } else {
      for (i = 0; i < DCTSIZE2; i++) {
        dtbl[i] = (DCTELEM)
          DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
                    (INT32) aanscales[i]),
              CONST_BITS+JPEG_DATA_PRECISION-BITS_IN_JSAMPLE-3);
      }
    }
      }
      fdct->pub.forward_DCT[ci] = forward_DCT;
      break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
    case JDCT_FLOAT:
      {
    /* For float AA&N FDCT 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
     * with adjustment if necessary.
     * What's actually stored is 1/divisor so that the inner loop can
     * use a multiplication rather than a division.
     */
    FAST_FLOAT * fdtbl = (FAST_FLOAT *) compptr->dct_table;
    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 BITS_IN_JSAMPLE == JPEG_DATA_PRECISION
 
    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] *
              (compptr->component_needed ? 16.0 : 8.0)));
#else
    double extrafactor = compptr->component_needed ? 16.0 : 8.0;
 
    /* Adjust extra factor */
#if BITS_IN_JSAMPLE < JPEG_DATA_PRECISION
    i = JPEG_DATA_PRECISION - BITS_IN_JSAMPLE;
    do { extrafactor *= 0.5; } while (--i);
#else
    i = BITS_IN_JSAMPLE - JPEG_DATA_PRECISION;
    do { extrafactor *= 2.0; } while (--i);
#endif
 
    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] *
              extrafactor));
#endif
        i++;
      }
    }
      }
      fdct->pub.forward_DCT[ci] = forward_DCT_float;
      break;
#endif
    default:
      ERREXIT(cinfo, JERR_NOT_COMPILED);
    }
  }
}
 
 
/*
 * Initialize FDCT manager.
 */
 
GLOBAL(void)
jinit_forward_dct (j_compress_ptr cinfo)
{
  my_fdct_ptr fdct;
  int ci;
  jpeg_component_info *compptr;
 
  fdct = (my_fdct_ptr) (*cinfo->mem->alloc_small)
    ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_fdct_controller));
  cinfo->fdct = &fdct->pub;
  fdct->pub.start_pass = start_pass_fdctmgr;
 
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    /* Allocate a divisor table for each component */
    compptr->dct_table = (*cinfo->mem->alloc_small)
      ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(divisor_table));
  }
}