media/libjpeg/jidctflt.c
author Andreea Pavel <apavel@mozilla.com>
Wed, 18 Sep 2019 13:53:34 +0300
changeset 493713 a3a081ae714f1123bdc23c9d9ef53dfaa783a8de
parent 440267 a3fa8bb51b3c4a1d3751fddf3db69bc770eb8aae
permissions -rw-r--r--
Backed out 9 changesets (bug 1578661) for lints failure at ServoCSSPropList.py a=backout Backed out changeset d16463e5698c (bug 1578661) Backed out changeset c6d64ac858ba (bug 1578661) Backed out changeset db306f1467f7 (bug 1578661) Backed out changeset 273535aab82d (bug 1578661) Backed out changeset f643262a8c25 (bug 1578661) Backed out changeset b0db409ada96 (bug 1578661) Backed out changeset dc96d13728e0 (bug 1578661) Backed out changeset 11e1e8f0a1b7 (bug 1578661) Backed out changeset 6dd7a0d914d9 (bug 1578661)

/*
 * jidctflt.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1998, Thomas G. Lane.
 * Modified 2010 by Guido Vollbeding.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2014, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains a floating-point implementation of the
 * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
 * must also perform dequantization of the input coefficients.
 *
 * This implementation should be more accurate than either of the integer
 * IDCT 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 IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
 * on each row (or vice versa, but it's more convenient to emit a row at
 * a time).  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.ijg).  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


/* Dequantize a coefficient by multiplying it by the multiplier-table
 * entry; produce a float result.
 */

#define DEQUANTIZE(coef, quantval)  (((FAST_FLOAT)(coef)) * (quantval))


/*
 * Perform dequantization and inverse DCT on one block of coefficients.
 */

GLOBAL(void)
jpeg_idct_float(j_decompress_ptr cinfo, jpeg_component_info *compptr,
                JCOEFPTR coef_block, JSAMPARRAY output_buf,
                JDIMENSION output_col)
{
  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
  FAST_FLOAT z5, z10, z11, z12, z13;
  JCOEFPTR inptr;
  FLOAT_MULT_TYPE *quantptr;
  FAST_FLOAT *wsptr;
  JSAMPROW outptr;
  JSAMPLE *range_limit = cinfo->sample_range_limit;
  int ctr;
  FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
#define _0_125  ((FLOAT_MULT_TYPE)0.125)

  /* Pass 1: process columns from input, store into work array. */

  inptr = coef_block;
  quantptr = (FLOAT_MULT_TYPE *)compptr->dct_table;
  wsptr = workspace;
  for (ctr = DCTSIZE; ctr > 0; ctr--) {
    /* Due to quantization, we will usually find that many of the input
     * coefficients are zero, especially the AC terms.  We can exploit this
     * by short-circuiting the IDCT calculation for any column in which all
     * the AC terms are zero.  In that case each output is equal to the
     * DC coefficient (with scale factor as needed).
     * With typical images and quantization tables, half or more of the
     * column DCT calculations can be simplified this way.
     */

    if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 &&
        inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 4] == 0 &&
        inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 6] == 0 &&
        inptr[DCTSIZE * 7] == 0) {
      /* AC terms all zero */
      FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE * 0],
                                    quantptr[DCTSIZE * 0] * _0_125);

      wsptr[DCTSIZE * 0] = dcval;
      wsptr[DCTSIZE * 1] = dcval;
      wsptr[DCTSIZE * 2] = dcval;
      wsptr[DCTSIZE * 3] = dcval;
      wsptr[DCTSIZE * 4] = dcval;
      wsptr[DCTSIZE * 5] = dcval;
      wsptr[DCTSIZE * 6] = dcval;
      wsptr[DCTSIZE * 7] = dcval;

      inptr++;                  /* advance pointers to next column */
      quantptr++;
      wsptr++;
      continue;
    }

    /* Even part */

    tmp0 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] * _0_125);
    tmp1 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] * _0_125);
    tmp2 = DEQUANTIZE(inptr[DCTSIZE * 4], quantptr[DCTSIZE * 4] * _0_125);
    tmp3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] * _0_125);

    tmp10 = tmp0 + tmp2;        /* phase 3 */
    tmp11 = tmp0 - tmp2;

    tmp13 = tmp1 + tmp3;        /* phases 5-3 */
    tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT)1.414213562) - tmp13; /* 2*c4 */

    tmp0 = tmp10 + tmp13;       /* phase 2 */
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;

    /* Odd part */

    tmp4 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] * _0_125);
    tmp5 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] * _0_125);
    tmp6 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] * _0_125);
    tmp7 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] * _0_125);

    z13 = tmp6 + tmp5;          /* phase 6 */
    z10 = tmp6 - tmp5;
    z11 = tmp4 + tmp7;
    z12 = tmp4 - tmp7;

    tmp7 = z11 + z13;           /* phase 5 */
    tmp11 = (z11 - z13) * ((FAST_FLOAT)1.414213562); /* 2*c4 */

    z5 = (z10 + z12) * ((FAST_FLOAT)1.847759065); /* 2*c2 */
    tmp10 = z5 - z12 * ((FAST_FLOAT)1.082392200); /* 2*(c2-c6) */
    tmp12 = z5 - z10 * ((FAST_FLOAT)2.613125930); /* 2*(c2+c6) */

    tmp6 = tmp12 - tmp7;        /* phase 2 */
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 - tmp5;

    wsptr[DCTSIZE * 0] = tmp0 + tmp7;
    wsptr[DCTSIZE * 7] = tmp0 - tmp7;
    wsptr[DCTSIZE * 1] = tmp1 + tmp6;
    wsptr[DCTSIZE * 6] = tmp1 - tmp6;
    wsptr[DCTSIZE * 2] = tmp2 + tmp5;
    wsptr[DCTSIZE * 5] = tmp2 - tmp5;
    wsptr[DCTSIZE * 3] = tmp3 + tmp4;
    wsptr[DCTSIZE * 4] = tmp3 - tmp4;

    inptr++;                    /* advance pointers to next column */
    quantptr++;
    wsptr++;
  }

  /* Pass 2: process rows from work array, store into output array. */

  wsptr = workspace;
  for (ctr = 0; ctr < DCTSIZE; ctr++) {
    outptr = output_buf[ctr] + output_col;
    /* Rows of zeroes can be exploited in the same way as we did with columns.
     * However, the column calculation has created many nonzero AC terms, so
     * the simplification applies less often (typically 5% to 10% of the time).
     * And testing floats for zero is relatively expensive, so we don't bother.
     */

    /* Even part */

    /* Apply signed->unsigned and prepare float->int conversion */
    z5 = wsptr[0] + ((FAST_FLOAT)CENTERJSAMPLE + (FAST_FLOAT)0.5);
    tmp10 = z5 + wsptr[4];
    tmp11 = z5 - wsptr[4];

    tmp13 = wsptr[2] + wsptr[6];
    tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT)1.414213562) - tmp13;

    tmp0 = tmp10 + tmp13;
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;

    /* Odd part */

    z13 = wsptr[5] + wsptr[3];
    z10 = wsptr[5] - wsptr[3];
    z11 = wsptr[1] + wsptr[7];
    z12 = wsptr[1] - wsptr[7];

    tmp7 = z11 + z13;
    tmp11 = (z11 - z13) * ((FAST_FLOAT)1.414213562);

    z5 = (z10 + z12) * ((FAST_FLOAT)1.847759065); /* 2*c2 */
    tmp10 = z5 - z12 * ((FAST_FLOAT)1.082392200); /* 2*(c2-c6) */
    tmp12 = z5 - z10 * ((FAST_FLOAT)2.613125930); /* 2*(c2+c6) */

    tmp6 = tmp12 - tmp7;
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 - tmp5;

    /* Final output stage: float->int conversion and range-limit */

    outptr[0] = range_limit[((int)(tmp0 + tmp7)) & RANGE_MASK];
    outptr[7] = range_limit[((int)(tmp0 - tmp7)) & RANGE_MASK];
    outptr[1] = range_limit[((int)(tmp1 + tmp6)) & RANGE_MASK];
    outptr[6] = range_limit[((int)(tmp1 - tmp6)) & RANGE_MASK];
    outptr[2] = range_limit[((int)(tmp2 + tmp5)) & RANGE_MASK];
    outptr[5] = range_limit[((int)(tmp2 - tmp5)) & RANGE_MASK];
    outptr[3] = range_limit[((int)(tmp3 + tmp4)) & RANGE_MASK];
    outptr[4] = range_limit[((int)(tmp3 - tmp4)) & RANGE_MASK];

    wsptr += DCTSIZE;           /* advance pointer to next row */
  }
}

#endif /* DCT_FLOAT_SUPPORTED */