text: /*
   * jfdctflt.c
   *
   * Copyright (C) 1994-1996, Thomas G. Lane.
   * Modified 2003-2009 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 a floating-point implementation of the
   * forward DCT (Discrete Cosine Transform).
   *
   * This implementation should be more accurate than either of the integer
   * DCT implementations.  However, it may not give the same results on all
   * machines because of differences in roundoff behavior.  Speed will depend
   * on the hardware's floating point capacity.
   *
   * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
   * on each column.  Direct algorithms are also available, but they are
   * much more complex and seem not to be any faster when reduced to code.
   *
   * This implementation is based on Arai, Agui, and Nakajima's algorithm for
   * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
   * Japanese, but the algorithm is described in the Pennebaker & Mitchell
   * JPEG textbook (see REFERENCES section in file README).  The following code
   * is based directly on figure 4-8 in P&M.
   * While an 8-point DCT cannot be done in less than 11 multiplies, it is
   * possible to arrange the computation so that many of the multiplies are
   * simple scalings of the final outputs.  These multiplies can then be
   * folded into the multiplications or divisions by the JPEG quantization
   * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
   * to be done in the DCT itself.
   * The primary disadvantage of this method is that with a fixed-point
   * implementation, accuracy is lost due to imprecise representation of the
   * scaled quantization values.  However, that problem does not arise if
   * we use floating point arithmetic.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  #include "jdct.h"        /* Private declarations for DCT subsystem */
  
  #ifdef DCT_FLOAT_SUPPORTED
  
  
  /*
   * This module is specialized to the case DCTSIZE = 8.
   */
  
  #if DCTSIZE != 8
    Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  #endif
  
  
  /*
   * Perform the forward DCT on one block of samples.
   */
  
  GLOBAL(void)
  jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col)
  {
    FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
    FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
    FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
    FAST_FLOAT *dataptr;
    JSAMPROW elemptr;
    int ctr;
  
    /* Pass 1: process rows. */
  
    dataptr = data;
    for (ctr = 0; ctr < DCTSIZE; ctr++) {
      elemptr = sample_data[ctr] + start_col;
  
      /* Load data into workspace */
      tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]));
      tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]));
      tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]));
      tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]));
      tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]));
      tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]));
      tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]));
      tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]));
  
      /* Even part */
  
      tmp10 = tmp0 + tmp3;    /* phase 2 */
      tmp13 = tmp0 - tmp3;
      tmp11 = tmp1 + tmp2;
      tmp12 = tmp1 - tmp2;
  
      /* Apply unsigned->signed conversion */
      dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
      dataptr[4] = tmp10 - tmp11;
  
      z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
      dataptr[2] = tmp13 + z1;    /* phase 5 */
      dataptr[6] = tmp13 - z1;
  
      /* Odd part */
  
      tmp10 = tmp4 + tmp5;    /* phase 2 */
      tmp11 = tmp5 + tmp6;
      tmp12 = tmp6 + tmp7;
  
      /* The rotator is modified from fig 4-8 to avoid extra negations. */
      z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
      z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
      z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
      z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
  
      z11 = tmp7 + z3;        /* phase 5 */
      z13 = tmp7 - z3;
  
      dataptr[5] = z13 + z2;    /* phase 6 */
      dataptr[3] = z13 - z2;
      dataptr[1] = z11 + z4;
      dataptr[7] = z11 - z4;
  
      dataptr += DCTSIZE;        /* advance pointer to next row */
    }
  
    /* Pass 2: process columns. */
  
    dataptr = data;
    for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
      tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
      tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
      tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
      tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
      tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
      tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
      tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
      tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
  
      /* Even part */
  
      tmp10 = tmp0 + tmp3;    /* phase 2 */
      tmp13 = tmp0 - tmp3;
      tmp11 = tmp1 + tmp2;
      tmp12 = tmp1 - tmp2;
  
      dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
      dataptr[DCTSIZE*4] = tmp10 - tmp11;
  
      z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
      dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
      dataptr[DCTSIZE*6] = tmp13 - z1;
  
      /* Odd part */
  
      tmp10 = tmp4 + tmp5;    /* phase 2 */
      tmp11 = tmp5 + tmp6;
      tmp12 = tmp6 + tmp7;
  
      /* The rotator is modified from fig 4-8 to avoid extra negations. */
      z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
      z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
      z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
      z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
  
      z11 = tmp7 + z3;        /* phase 5 */
      z13 = tmp7 - z3;
  
      dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
      dataptr[DCTSIZE*3] = z13 - z2;
      dataptr[DCTSIZE*1] = z11 + z4;
      dataptr[DCTSIZE*7] = z11 - z4;
  
      dataptr++;            /* advance pointer to next column */
    }
  }
  
  #endif /* DCT_FLOAT_SUPPORTED */
  