text: //
  // Copyright (c) .NET Foundation and Contributors
  // Original work Copyright (c) 1994-1998, Thomas G. Lane
  // See LICENSE file in the project root for full license information.
  //
  
  /*
   * 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_X86:
          case JDCT_ISLOW_MMX:
          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_X86:
          case JDCT_IFAST_MMX:
          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 CLR_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((CLR_INT32)qtbl->quantval[i],
                      (CLR_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++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(GETJSAMPLE(*elemptr++) - CENTERJSAMPLE);
              *workspaceptr++ = (DCTELEM)(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 = (DCTELEM)(a/b)
  #else
  #define DIVIDE_BY(a,b)	if (a >= b) a = (DCTELEM)(a/b); else a = 0
  #endif
              if (temp < 0) {
                  temp = (DCTELEM)-temp;
                  temp = (DCTELEM)(temp + (qval >> 1));	/* for rounding */
                  DIVIDE_BY(temp, qval);
                  temp = (DCTELEM)-temp;
              }
              else {
                  temp = (DCTELEM)(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_MMX:
  #ifdef JPEG_MMX_SUPPORTED_NOT_IN_BUILD
          fdct->pub.forward_DCT = forward_DCT;
          fdct->do_dct = jpeg_fdct_islow_mmx;
          break;
  #endif
      case JDCT_ISLOW_X86:
  #ifdef JPEG_X86_SUPPORTED_NOT_IN_BUILD
          fdct->pub.forward_DCT = forward_DCT;
          fdct->do_dct = jpeg_fdct_islow_x86;
          break;
  #endif
      case JDCT_ISLOW:
          fdct->pub.forward_DCT = forward_DCT;
          fdct->do_dct = jpeg_fdct_islow;
          break;
  #endif
  #ifdef DCT_IFAST_SUPPORTED
      case JDCT_IFAST_MMX:
  #ifdef JPEG_MMX_SUPPORTED_NOT_IN_BUILD
          fdct->pub.forward_DCT = forward_DCT;
          fdct->do_dct = jpeg_fdct_ifast_mmx;
          break;
  #endif
      case JDCT_IFAST_X86:
  #ifdef JPEG_X86_SUPPORTED_NOT_IN_BUILD
          fdct->pub.forward_DCT = forward_DCT;
          fdct->do_dct = jpeg_fdct_ifast_x86;
          break;
  #endif
      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
      }
  }
  