xref: /utopia/UTPA2-700.0.x/modules/ojpd_vdec_v1/api/jpeg/cmodel/src/jidctfst.c (revision 53ee8cc121a030b8d368113ac3e966b4705770ef)

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//<MStar Software>
/*
 * jidctfst.c
 *
 * Copyright (C) 1994-1998, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains a fast, not so accurate integer implementation of the
 * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
 * must also perform dequantization of the input coefficients.
 *
 * 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).  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 fixed-point math,
 * accuracy is lost due to imprecise representation of the scaled
 * quantization values.  The smaller the quantization table entry, the less
 * precise the scaled value, so this implementation does worse with high-
 * quality-setting files than with low-quality ones.
 */

///#define JPEG_INTERNALS
///#include "jinclude.h"
///#include "jpeglib.h"
///#include "jdct.h"        /* Private declarations for DCT subsystem */
#include "jpegmain.h"
#include "apiJPEG.h"

#define DCTSIZE 8
#define BITS_IN_JSAMPLE 8
#define DCT_IFAST_SUPPORTED

#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)
#define DESCALE(x,n)  ((x) >> (n)) //=> speed a little with a compromise in accuracy
//#define DESCALE(x,n)  (((x) + ( ((int32)1) << ((n)-1))) >> (n))  //
#endif


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

typedef int DCTELEM;        /* 16 or 32 bits is fine */
#define MULTIPLY(var,cnst)  ((DCTELEM) DESCALE((var) * (cnst), 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))
#define DEQUANTIZE(coef,quantval)  (coef)
#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

#if 1///def USE_ACCURATE_ROUNDING
#define IDESCALE(x,n)  ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
//#define IDESCALE(x,n)  ( ( (int)(x) + (1 << ((n)-1)) ) >> (n) )
#else
#define IDESCALE(x,n)  ((int) IRIGHT_SHIFT(x, n))
#endif

#define IFAST_MULT_TYPE int

#define clamp(i) if (i & 0xFF00) i = (((~i) >> 15) & 0xFF);

/*
 * 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)
void jpeg_idct_ifast( JPEG_BLOCK_TYPE *data, U8 *Pdst_ptr )
{
    #define INT32   S32
    #define DCTSIZE2 64
    #define DCTSIZE 8

    DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
    DCTELEM tmp10, tmp11, tmp12, tmp13;
    DCTELEM z5, z10, z11, z12, z13;
    ///JCOEFPTR inptr;
    register JPEG_BLOCK_TYPE *inptr;
    IFAST_MULT_TYPE *quantptr;
    ///JSAMPROW outptr;
    U8 *outptr = Pdst_ptr;
    ///JSAMPLE *range_limit = IDCT_range_limit(cinfo);
    int ctr;
    ///int workspace[DCTSIZE2]; /* buffers data between passes */
    JPEG_BLOCK_TYPE workspace[DCTSIZE2];
    JPEG_BLOCK_TYPE *wsptr;
    ///SHIFT_TEMPS          /* for DESCALE */
    ///ISHIFT_TEMPS         /* for IDESCALE */
    S16 i;
//printf("jidctfst::jpeg_idct_ifast\n");
    /* Pass 1: process columns from input, store into work array. */

    inptr = data;
    ///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.
         */

        #if 1///ndef 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];
            int dcval = IDESCALE( wsptr[0], PASS1_BITS + 3 ) + 128;
            clamp( dcval );

            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 */
            outptr += DCTSIZE;
            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];
        */
        i = IDESCALE( tmp0 + tmp7, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[0] = ( U8 )i;
        i = IDESCALE( tmp0 - tmp7, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[7] = ( U8 )i;
        i = IDESCALE( tmp1 + tmp6, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[1] = ( U8 )i;
        i = IDESCALE( tmp1 - tmp6, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[6] = ( U8 )i;
        i = IDESCALE( tmp2 + tmp5, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[2] = ( U8 )i;
        i = IDESCALE( tmp2 - tmp5, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[5] = ( U8 )i;
        i = IDESCALE( tmp3 + tmp4, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[4] = ( U8 )i;
        i = IDESCALE( tmp3 - tmp4, PASS1_BITS + 3 ) + 128;
        clamp( i );
        outptr[3] = ( U8 )i;

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

#endif /* DCT_IFAST_SUPPORTED */