Subversion Repositories mpeg2fpga

/*

 * jrevdct.c

 *

 * Copyright (C) 1991, 1992, 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 the basic inverse-DCT transformation subroutine.

 *

 * This implementation is based on an algorithm described in

 *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT

 *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,

 *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.

 * The primary algorithm described there uses 11 multiplies and 29 adds.

 * We use their alternate method with 12 multiplies and 32 adds.

 * The advantage of this method is that no data path contains more than one

 * multiplication; this allows a very simple and accurate implementation in

 * scaled fixed-point arithmetic, with a minimal number of shifts.

 */

#include "dct.h"

#include <stdio.h>

/* We assume that right shift corresponds to signed division by 2 with

 * rounding towards minus infinity.  This is correct for typical "arithmetic

 * shift" instructions that shift in copies of the sign bit.  But some

 * C compilers implement >> with an unsigned shift.  For these machines you

 * must define RIGHT_SHIFT_IS_UNSIGNED.

 * RIGHT_SHIFT provides a proper signed right shift of an INT32 quantity.

 * It is only applied with constant shift counts.  SHIFT_TEMPS must be

 * included in the variables of any routine using RIGHT_SHIFT.

 */

#ifdef RIGHT_SHIFT_IS_UNSIGNED

#define SHIFT_TEMPS     INT32 shift_temp;

#define RIGHT_SHIFT(x,shft)  \

        ((shift_temp = (x)) < 0 ? \

         (shift_temp >> (shft)) | ((~((INT32) 0)) << (32-(shft))) : \

         (shift_temp >> (shft)))

#else

#define SHIFT_TEMPS

#define RIGHT_SHIFT(x,shft)     ((x) >> (shft))

#endif

/*

 * This routine is specialized to the case DCTSIZE = 8.

 */

#if DCTSIZE != 8

  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */

#endif

/*

 * A 2-D IDCT can be done by 1-D IDCT on each row followed by 1-D IDCT

 * on each column.  Direct algorithms are also available, but they are

 * much more complex and seem not to be any faster when reduced to code.

 *

 * 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.

 */

#ifdef EIGHT_BIT_SAMPLES

#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

#define ONE     ((INT32) 1)

#define CONST_SCALE (ONE << CONST_BITS)

/* Convert a positive real constant to an integer scaled by CONST_SCALE. */

#define FIX(x)  ((INT32) ((x) * CONST_SCALE + 0.5))

/* 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

/* Descale and correctly round an INT32 value that's scaled by N bits.

 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding

 * the fudge factor is correct for either sign of X.

 */

#define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)

/* 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;

 * this provides a useful speedup on many machines.

 * There is no way to specify a 16x16->32 multiply in portable C, but

 * some C compilers will do the right thing if you provide the correct

 * combination of casts.

 * NB: for 12-bit samples, a full 32-bit multiplication will be needed.

 */

#ifdef EIGHT_BIT_SAMPLES

#ifdef SHORTxSHORT_32           /* may work if 'int' is 32 bits */

#define MULTIPLY(var,const)  (((INT16) (var)) * ((INT16) (const)))

#endif

#ifdef SHORTxLCONST_32          /* known to work with Microsoft C 6.0 */

#define MULTIPLY(var,const)  (((INT16) (var)) * ((INT32) (const)))

#endif

#endif

#ifndef MULTIPLY                /* default definition */

#define MULTIPLY(var,const)  ((var) * (const))

#endif

/*

 * Perform the inverse DCT on one block of coefficients.

 */

void

j_rev_dct (DCTBLOCK data)

{

  register DCTELEM *dataptr;

  int i, j;

  FILE *idctdat;

  SHIFT_TEMPS

  dataptr = data;

  idctdat = fopen("idct-in", "w");

  for (i = 0; i <= 63; i++) {

    j = ((INT32)dataptr[i]) & 4095;

    fprintf(idctdat, "%x\n", j);

  }

  fclose(idctdat);

  system("./idct-verilog > idct-out");

  idctdat = fopen("idct-out", "r");

  for (i = 0; i <= 63; i++) {

    fscanf(idctdat, "%d", &j);

    dataptr[i] = j;

  }

  fclose(idctdat);

}