jidctfst.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 jidctint.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.
 *
 * The dequantized coefficients are not integers because the AA&N scaling
 * factors have been incorporated.  We represent them scaled up by PASS1_BITS,
 * so that the first and second IDCT rounds have the same input scaling.
 * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
 * avoid a descaling shift; this compromises accuracy rather drastically
 * for small quantization table entries, but it saves a lot of shifts.
 * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
 * so we use a much larger scaling factor to preserve accuracy.
 *
 * 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).
 */

#if BITS_IN_JSAMPLE == 8
#define CONST_BITS 8
#define PASS1_BITS 2
#else
#define CONST_BITS 8
#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 == 8
#define FIX_1_082392200 ((INT32)277) /* FIX(1.082392200) */
#define FIX_1_414213562 ((INT32)362) /* FIX(1.414213562) */
#define FIX_1_847759065 ((INT32)473) /* FIX(1.847759065) */
#define FIX_2_613125930 ((INT32)669) /* FIX(2.613125930) */
#else
#define FIX_1_082392200 FIX(1.082392200)
#define FIX_1_414213562 FIX(1.414213562)
#define FIX_1_847759065 FIX(1.847759065)
#define FIX_2_613125930 FIX(2.613125930)
#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))

/* Dequantize a coefficient by multiplying it by the multiplier-table
 * entry; produce a DCTELEM result.  For 8-bit data a 16x16->16
 * multiplication will do.  For 12-bit data, the multiplier table is
 * declared INT32, so a 32-bit multiply will be used.
 */

#if BITS_IN_JSAMPLE == 8
#define DEQUANTIZE(coef, quantval) (((IFAST_MULT_TYPE)(coef)) * (quantval))
#else
#define DEQUANTIZE(coef, quantval) \
        DESCALE((coef) * (quantval), IFAST_SCALE_BITS - PASS1_BITS)
#endif

/* Like DESCALE, but applies to a DCTELEM and produces an int.
 * We assume that int right shift is unsigned if INT32 right shift is.
 */

#ifdef RIGHT_SHIFT_IS_UNSIGNED
#define ISHIFT_TEMPS DCTELEM ishift_temp;
#if BITS_IN_JSAMPLE == 8
#define DCTELEMBITS 16 /* DCTELEM may be 16 or 32 bits */
#else
#define DCTELEMBITS 32 /* DCTELEM must be 32 bits */
#endif
#define IRIGHT_SHIFT(x, shft)                              \
        ((ishift_temp = (x)) < 0                               \
                 ? (ishift_temp >> (shft)) |                       \
                           ((~((DCTELEM)0)) << (DCTELEMBITS - (shft))) \
                 : (ishift_temp >> (shft)))
#else
#define ISHIFT_TEMPS
#define IRIGHT_SHIFT(x, shft) ((x) >> (shft))
#endif

#ifdef USE_ACCURATE_ROUNDING
#define IDESCALE(x, n) ((int)IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
#else
#define IDESCALE(x, n) ((int)IRIGHT_SHIFT(x, n))
#endif

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

           GLOBAL(void) jpeg_idct_ifast(
                   j_decompress_ptr cinfo, jpeg_component_info* compptr,
                   JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)
{
        DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
        DCTELEM tmp10, tmp11, tmp12, tmp13;
        DCTELEM z5, z10, z11, z12, z13;
        JCOEFPTR inptr;
        IFAST_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 /* for DESCALE */
                ISHIFT_TEMPS /* for IDESCALE */

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

                inptr = coef_block;
        quantptr = (IFAST_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 =
                                (int)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 = MULTIPLY(tmp1 - tmp3, FIX_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 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */

                z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
                tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
                tmp12 = MULTIPLY(z10, -FIX_2_613125930) + z5; /* -2*(c2+c6) */

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

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

                tmp10 = ((DCTELEM)wsptr[0] + (DCTELEM)wsptr[4]);
                tmp11 = ((DCTELEM)wsptr[0] - (DCTELEM)wsptr[4]);

                tmp13 = ((DCTELEM)wsptr[2] + (DCTELEM)wsptr[6]);
                tmp12 =
                        MULTIPLY((DCTELEM)wsptr[2] - (DCTELEM)wsptr[6], FIX_1_414213562) -
                        tmp13;

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

                /* Odd part */

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

                tmp7 = z11 + z13; /* phase 5 */
                tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */

                z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
                tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
                tmp12 = MULTIPLY(z10, -FIX_2_613125930) + z5; /* -2*(c2+c6) */

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

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

                outptr[0] =
                        range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS + 3) & RANGE_MASK];
                outptr[7] =
                        range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS + 3) & RANGE_MASK];
                outptr[1] =
                        range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS + 3) & RANGE_MASK];
                outptr[6] =
                        range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS + 3) & RANGE_MASK];
                outptr[2] =
                        range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS + 3) & RANGE_MASK];
                outptr[5] =
                        range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS + 3) & RANGE_MASK];
                outptr[4] =
                        range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS + 3) & RANGE_MASK];
                outptr[3] =
                        range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS + 3) & RANGE_MASK];

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

#endif /* DCT_IFAST_SUPPORTED */