jidctint.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_ISLOW_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

/*
 * The poop on this scaling stuff is as follows:
 *
 * Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
 * larger than the true IDCT outputs.  The final outputs are therefore
 * a factor of N larger than desired; since N=8 this can be cured by
 * a simple right shift at the end of the algorithm.  The advantage of
 * this arrangement is that we save two multiplications per 1-D IDCT,
 * because the y0 and y4 inputs need not be divided by sqrt(N).
 *
 * We have to do addition and subtraction of the integer inputs, which
 * is no problem, and multiplication by fractional constants, which is
 * a problem to do in integer arithmetic.  We multiply all the constants
 * by CONST_SCALE and convert them to integer constants (thus retaining
 * CONST_BITS bits of precision in the constants).  After doing a
 * multiplication we have to divide the product by CONST_SCALE, with proper
 * rounding, to produce the correct output.  This division can be done
 * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
 * as long as possible so that partial sums can be added together with
 * full fractional precision.
 *
 * The outputs of the first pass are scaled up by PASS1_BITS bits so that
 * they are represented to better-than-integral precision.  These outputs
 * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
 * with the recommended scaling.  (To scale up 12-bit sample data further, an
 * intermediate INT32 array would be needed.)
 *
 * To avoid overflow of the 32-bit intermediate results in pass 2, we must
 * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
 * shows that the values given below are the most effective.
 */

#if BITS_IN_JSAMPLE == 8
#define CONST_BITS 13
#define PASS1_BITS 2
#else
#define CONST_BITS 13
#define PASS1_BITS 1 /* lose a little precision to avoid overflow */
#endif

/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
 * causing a lot of useless floating-point operations at run time.
 * To get around this we use the following pre-calculated constants.
 * If you change CONST_BITS you may want to add appropriate values.
 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
 */

#if CONST_BITS == 13
#define FIX_0_298631336 ((INT32)2446) /* FIX(0.298631336) */
#define FIX_0_390180644 ((INT32)3196) /* FIX(0.390180644) */
#define FIX_0_541196100 ((INT32)4433) /* FIX(0.541196100) */
#define FIX_0_765366865 ((INT32)6270) /* FIX(0.765366865) */
#define FIX_0_899976223 ((INT32)7373) /* FIX(0.899976223) */
#define FIX_1_175875602 ((INT32)9633) /* FIX(1.175875602) */
#define FIX_1_501321110 ((INT32)12299) /* FIX(1.501321110) */
#define FIX_1_847759065 ((INT32)15137) /* FIX(1.847759065) */
#define FIX_1_961570560 ((INT32)16069) /* FIX(1.961570560) */
#define FIX_2_053119869 ((INT32)16819) /* FIX(2.053119869) */
#define FIX_2_562915447 ((INT32)20995) /* FIX(2.562915447) */
#define FIX_3_072711026 ((INT32)25172) /* FIX(3.072711026) */
#else
#define FIX_0_298631336 FIX(0.298631336)
#define FIX_0_390180644 FIX(0.390180644)
#define FIX_0_541196100 FIX(0.541196100)
#define FIX_0_765366865 FIX(0.765366865)
#define FIX_0_899976223 FIX(0.899976223)
#define FIX_1_175875602 FIX(1.175875602)
#define FIX_1_501321110 FIX(1.501321110)
#define FIX_1_847759065 FIX(1.847759065)
#define FIX_1_961570560 FIX(1.961570560)
#define FIX_2_053119869 FIX(2.053119869)
#define FIX_2_562915447 FIX(2.562915447)
#define FIX_3_072711026 FIX(3.072711026)
#endif

/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
 * For 8-bit samples with the recommended scaling, all the variable
 * and constant values involved are no more than 16 bits wide, so a
 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
 * For 12-bit samples, a full 32-bit multiplication will be needed.
 */

#if BITS_IN_JSAMPLE == 8
#define MULTIPLY(var, const) MULTIPLY16C16(var, const)
#else
#define MULTIPLY(var, const) ((var) * (const))
#endif

/* Dequantize a coefficient by multiplying it by the multiplier-table
 * entry; produce an int result.  In this module, both inputs and result
 * are 16 bits or less, so either int or short multiply will work.
 */

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

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

           GLOBAL(void) jpeg_idct_islow(
                   j_decompress_ptr cinfo, jpeg_component_info* compptr,
                   JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)
{
        INT32 tmp0, tmp1, tmp2, tmp3;
        INT32 tmp10, tmp11, tmp12, tmp13;
        INT32 z1, z2, z3, z4, z5;
        JCOEFPTR inptr;
        ISLOW_MULT_TYPE* quantptr;
        int* wsptr;
        JSAMPROW outptr;
        JSAMPLE* range_limit = IDCT_range_limit(cinfo);
        int ctr;
        int workspace[DCTSIZE2]; /* buffers data between passes */
        SHIFT_TEMPS

        /* Pass 1: process columns from input, store into work array. */
        /* Note results are scaled up by sqrt(8) compared to a true IDCT; */
        /* furthermore, we scale the results by 2**PASS1_BITS. */

        inptr = coef_block;
        quantptr = (ISLOW_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 */
                        int dcval = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0])
                                                << PASS1_BITS;

                        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: reverse the even part of the forward DCT. */
                /* The rotator is sqrt(2)*c(-6). */

                z2 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2]);
                z3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6]);

                z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
                tmp2 = z1 + MULTIPLY(z3, -FIX_1_847759065);
                tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);

                z2 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
                z3 = DEQUANTIZE(inptr[DCTSIZE * 4], quantptr[DCTSIZE * 4]);

                tmp0 = (z2 + z3) << CONST_BITS;
                tmp1 = (z2 - z3) << CONST_BITS;

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

                /* Odd part per figure 8; the matrix is unitary and hence its
                 * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
                 */

                tmp0 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
                tmp1 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
                tmp2 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
                tmp3 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);

                z1 = tmp0 + tmp3;
                z2 = tmp1 + tmp2;
                z3 = tmp0 + tmp2;
                z4 = tmp1 + tmp3;
                z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

                tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
                tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
                tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
                tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
                z1 = MULTIPLY(z1, -FIX_0_899976223); /* sqrt(2) * (c7-c3) */
                z2 = MULTIPLY(z2, -FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
                z3 = MULTIPLY(z3, -FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
                z4 = MULTIPLY(z4, -FIX_0_390180644); /* sqrt(2) * (c5-c3) */

                z3 += z5;
                z4 += z5;

                tmp0 += z1 + z3;
                tmp1 += z2 + z4;
                tmp2 += z2 + z3;
                tmp3 += z1 + z4;

                /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */

                wsptr[DCTSIZE * 0] =
                        (int)DESCALE(tmp10 + tmp3, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 7] =
                        (int)DESCALE(tmp10 - tmp3, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 1] =
                        (int)DESCALE(tmp11 + tmp2, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 6] =
                        (int)DESCALE(tmp11 - tmp2, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 2] =
                        (int)DESCALE(tmp12 + tmp1, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 5] =
                        (int)DESCALE(tmp12 - tmp1, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 3] =
                        (int)DESCALE(tmp13 + tmp0, CONST_BITS - PASS1_BITS);
                wsptr[DCTSIZE * 4] =
                        (int)DESCALE(tmp13 - tmp0, CONST_BITS - PASS1_BITS);

                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, */
        /* and also undo the PASS1_BITS scaling. */

        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).
 * On machines with very fast multiplication, it's possible that the
 * test takes more time than it's worth.  In that case this section
 * may be commented out.
 */

#ifndef NO_ZERO_ROW_TEST
                if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
                        wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0)
                {
                        /* AC terms all zero */
                        JSAMPLE dcval =
                                range_limit[(int)DESCALE((INT32)wsptr[0], PASS1_BITS + 3) &
                                                        RANGE_MASK];

                        outptr[0] = dcval;
                        outptr[1] = dcval;
                        outptr[2] = dcval;
                        outptr[3] = dcval;
                        outptr[4] = dcval;
                        outptr[5] = dcval;
                        outptr[6] = dcval;
                        outptr[7] = dcval;

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

                /* Even part: reverse the even part of the forward DCT. */
                /* The rotator is sqrt(2)*c(-6). */

                z2 = (INT32)wsptr[2];
                z3 = (INT32)wsptr[6];

                z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
                tmp2 = z1 + MULTIPLY(z3, -FIX_1_847759065);
                tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);

                tmp0 = ((INT32)wsptr[0] + (INT32)wsptr[4]) << CONST_BITS;
                tmp1 = ((INT32)wsptr[0] - (INT32)wsptr[4]) << CONST_BITS;

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

                /* Odd part per figure 8; the matrix is unitary and hence its
                 * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
                 */

                tmp0 = (INT32)wsptr[7];
                tmp1 = (INT32)wsptr[5];
                tmp2 = (INT32)wsptr[3];
                tmp3 = (INT32)wsptr[1];

                z1 = tmp0 + tmp3;
                z2 = tmp1 + tmp2;
                z3 = tmp0 + tmp2;
                z4 = tmp1 + tmp3;
                z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

                tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
                tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
                tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
                tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
                z1 = MULTIPLY(z1, -FIX_0_899976223); /* sqrt(2) * (c7-c3) */
                z2 = MULTIPLY(z2, -FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
                z3 = MULTIPLY(z3, -FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
                z4 = MULTIPLY(z4, -FIX_0_390180644); /* sqrt(2) * (c5-c3) */

                z3 += z5;
                z4 += z5;

                tmp0 += z1 + z3;
                tmp1 += z2 + z4;
                tmp2 += z2 + z3;
                tmp3 += z1 + z4;

                /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */

                outptr[0] = range_limit[(int)DESCALE(
                                                                        tmp10 + tmp3, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[7] = range_limit[(int)DESCALE(
                                                                        tmp10 - tmp3, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[1] = range_limit[(int)DESCALE(
                                                                        tmp11 + tmp2, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[6] = range_limit[(int)DESCALE(
                                                                        tmp11 - tmp2, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[2] = range_limit[(int)DESCALE(
                                                                        tmp12 + tmp1, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[5] = range_limit[(int)DESCALE(
                                                                        tmp12 - tmp1, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[3] = range_limit[(int)DESCALE(
                                                                        tmp13 + tmp0, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];
                outptr[4] = range_limit[(int)DESCALE(
                                                                        tmp13 - tmp0, CONST_BITS + PASS1_BITS + 3) &
                                                                RANGE_MASK];

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

#endif /* DCT_ISLOW_SUPPORTED */