jidctflt.cpp

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "mrpt_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 = IDCT_range_limit(cinfo);
        int ctr;
        FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
        SHIFT_TEMPS

        /* 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]);

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

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

                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 = ((FAST_FLOAT)1.082392200) * z12 - z5; /* 2*(c2-c6) */
                tmp12 = ((FAST_FLOAT)-2.613125930) * z10 + z5; /* -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 * 4] = tmp3 + tmp4;
                wsptr[DCTSIZE * 3] = tmp3 - tmp4;

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

        /* Pass 2: process rows from work array, store into output array. */
        /* Note that we must descale the results by a factor of 8 == 2**3. */

        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 */

                tmp10 = wsptr[0] + wsptr[4];
                tmp11 = wsptr[0] - 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 = ((FAST_FLOAT)1.082392200) * z12 - z5; /* 2*(c2-c6) */
                tmp12 = ((FAST_FLOAT)-2.613125930) * z10 + z5; /* -2*(c2+c6) */

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

                /* Final output stage: scale down by a factor of 8 and range-limit */

                outptr[0] =
                        range_limit[(int)DESCALE((INT32)(tmp0 + tmp7), 3) & RANGE_MASK];
                outptr[7] =
                        range_limit[(int)DESCALE((INT32)(tmp0 - tmp7), 3) & RANGE_MASK];
                outptr[1] =
                        range_limit[(int)DESCALE((INT32)(tmp1 + tmp6), 3) & RANGE_MASK];
                outptr[6] =
                        range_limit[(int)DESCALE((INT32)(tmp1 - tmp6), 3) & RANGE_MASK];
                outptr[2] =
                        range_limit[(int)DESCALE((INT32)(tmp2 + tmp5), 3) & RANGE_MASK];
                outptr[5] =
                        range_limit[(int)DESCALE((INT32)(tmp2 - tmp5), 3) & RANGE_MASK];
                outptr[4] =
                        range_limit[(int)DESCALE((INT32)(tmp3 + tmp4), 3) & RANGE_MASK];
                outptr[3] =
                        range_limit[(int)DESCALE((INT32)(tmp3 - tmp4), 3) & RANGE_MASK];

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

#endif /* DCT_FLOAT_SUPPORTED */