jfdctfst.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_IFAST_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

/* Scaling decisions are generally the same as in the LL&M algorithm;
 * see jfdctint.c for more details.  However, we choose to descale
 * (right shift) multiplication products as soon as they are formed,
 * rather than carrying additional fractional bits into subsequent additions.
 * This compromises accuracy slightly, but it lets us save a few shifts.
 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
 * everywhere except in the multiplications proper; this saves a good deal
 * of work on 16-bit-int machines.
 *
 * Again to save a few shifts, the intermediate results between pass 1 and
 * pass 2 are not upscaled, but are represented only to integral precision.
 *
 * A final compromise is to represent the multiplicative constants to only
 * 8 fractional bits, rather than 13.  This saves some shifting work on some
 * machines, and may also reduce the cost of multiplication (since there
 * are fewer one-bits in the constants).
 */

#define CONST_BITS 8

/* 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 == 8
#define FIX_0_382683433 ((INT32)98) /* FIX(0.382683433) */
#define FIX_0_541196100 ((INT32)139) /* FIX(0.541196100) */
#define FIX_0_707106781 ((INT32)181) /* FIX(0.707106781) */
#define FIX_1_306562965 ((INT32)334) /* FIX(1.306562965) */
#else
#define FIX_0_382683433 FIX(0.382683433)
#define FIX_0_541196100 FIX(0.541196100)
#define FIX_0_707106781 FIX(0.707106781)
#define FIX_1_306562965 FIX(1.306562965)
#endif

/* We can gain a little more speed, with a further compromise in accuracy,
 * by omitting the addition in a descaling shift.  This yields an incorrectly
 * rounded result half the time...
 */

#ifndef USE_ACCURATE_ROUNDING
#undef DESCALE
#define DESCALE(x, n) RIGHT_SHIFT(x, n)
#endif

/* Multiply a DCTELEM variable by an INT32 constant, and immediately
 * descale to yield a DCTELEM result.
 */

#define MULTIPLY(var, const) ((DCTELEM)DESCALE((var) * (const), CONST_BITS))

           /*
                * Perform the forward DCT on one block of samples.
                */

           GLOBAL(void) jpeg_fdct_ifast(DCTELEM* data)
{
        DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
        DCTELEM tmp10, tmp11, tmp12, tmp13;
        DCTELEM z1, z2, z3, z4, z5, z11, z13;
        DCTELEM* dataptr;
        int ctr;
        SHIFT_TEMPS

        /* Pass 1: process rows. */

        dataptr = data;
        for (ctr = DCTSIZE - 1; ctr >= 0; ctr--)
        {
                tmp0 = dataptr[0] + dataptr[7];
                tmp7 = dataptr[0] - dataptr[7];
                tmp1 = dataptr[1] + dataptr[6];
                tmp6 = dataptr[1] - dataptr[6];
                tmp2 = dataptr[2] + dataptr[5];
                tmp5 = dataptr[2] - dataptr[5];
                tmp3 = dataptr[3] + dataptr[4];
                tmp4 = dataptr[3] - dataptr[4];

                /* Even part */

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

                dataptr[0] = tmp10 + tmp11; /* phase 3 */
                dataptr[4] = tmp10 - tmp11;

                z1 = MULTIPLY(tmp12 + tmp13, FIX_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 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
                z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
                z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
                z3 = MULTIPLY(tmp11, FIX_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 = MULTIPLY(tmp12 + tmp13, FIX_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 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
                z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
                z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
                z3 = MULTIPLY(tmp11, FIX_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_IFAST_SUPPORTED */