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[/] [mpeg2fpga/] [trunk/] [tools/] [ieee1180/] [ieee1180/] [jrevdct.c] - Blame information for rev 2

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/*
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 * jrevdct.c
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 *
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 * Copyright (C) 1991, 1992, Thomas G. Lane.
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 * This file is part of the Independent JPEG Group's software.
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 * For conditions of distribution and use, see the accompanying README file.
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 *
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 * This file contains the basic inverse-DCT transformation subroutine.
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 *
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 * This implementation is based on an algorithm described in
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 *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
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 *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
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 *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
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 * The primary algorithm described there uses 11 multiplies and 29 adds.
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 * We use their alternate method with 12 multiplies and 32 adds.
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 * The advantage of this method is that no data path contains more than one
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 * multiplication; this allows a very simple and accurate implementation in
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 * scaled fixed-point arithmetic, with a minimal number of shifts.
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 */
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#include "dct.h"
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#include <stdio.h>
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/* We assume that right shift corresponds to signed division by 2 with
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 * rounding towards minus infinity.  This is correct for typical "arithmetic
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 * shift" instructions that shift in copies of the sign bit.  But some
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 * C compilers implement >> with an unsigned shift.  For these machines you
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 * must define RIGHT_SHIFT_IS_UNSIGNED.
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 * RIGHT_SHIFT provides a proper signed right shift of an INT32 quantity.
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 * It is only applied with constant shift counts.  SHIFT_TEMPS must be
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 * included in the variables of any routine using RIGHT_SHIFT.
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 */
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#ifdef RIGHT_SHIFT_IS_UNSIGNED
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#define SHIFT_TEMPS     INT32 shift_temp;
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#define RIGHT_SHIFT(x,shft)  \
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        ((shift_temp = (x)) < 0 ? \
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         (shift_temp >> (shft)) | ((~((INT32) 0)) << (32-(shft))) : \
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         (shift_temp >> (shft)))
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#else
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#define SHIFT_TEMPS
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#define RIGHT_SHIFT(x,shft)     ((x) >> (shft))
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#endif
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/*
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 * This routine is specialized to the case DCTSIZE = 8.
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 */
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#if DCTSIZE != 8
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  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
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#endif
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/*
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 * A 2-D IDCT can be done by 1-D IDCT on each row followed by 1-D IDCT
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 * on each column.  Direct algorithms are also available, but they are
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 * much more complex and seem not to be any faster when reduced to code.
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 *
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 * The poop on this scaling stuff is as follows:
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 *
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 * Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
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 * larger than the true IDCT outputs.  The final outputs are therefore
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 * a factor of N larger than desired; since N=8 this can be cured by
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 * a simple right shift at the end of the algorithm.  The advantage of
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 * this arrangement is that we save two multiplications per 1-D IDCT,
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 * because the y0 and y4 inputs need not be divided by sqrt(N).
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 *
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 * We have to do addition and subtraction of the integer inputs, which
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 * is no problem, and multiplication by fractional constants, which is
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 * a problem to do in integer arithmetic.  We multiply all the constants
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 * by CONST_SCALE and convert them to integer constants (thus retaining
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 * CONST_BITS bits of precision in the constants).  After doing a
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 * multiplication we have to divide the product by CONST_SCALE, with proper
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 * rounding, to produce the correct output.  This division can be done
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 * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
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 * as long as possible so that partial sums can be added together with
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 * full fractional precision.
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 *
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 * The outputs of the first pass are scaled up by PASS1_BITS bits so that
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 * they are represented to better-than-integral precision.  These outputs
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 * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
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 * with the recommended scaling.  (To scale up 12-bit sample data further, an
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 * intermediate INT32 array would be needed.)
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 *
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 * To avoid overflow of the 32-bit intermediate results in pass 2, we must
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 * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
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 * shows that the values given below are the most effective.
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 */
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#ifdef EIGHT_BIT_SAMPLES
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#define CONST_BITS  13
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#define PASS1_BITS  2
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#else
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#define CONST_BITS  13
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#define PASS1_BITS  1           /* lose a little precision to avoid overflow */
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#endif
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#define ONE     ((INT32) 1)
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#define CONST_SCALE (ONE << CONST_BITS)
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/* Convert a positive real constant to an integer scaled by CONST_SCALE. */
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#define FIX(x)  ((INT32) ((x) * CONST_SCALE + 0.5))
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/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
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 * causing a lot of useless floating-point operations at run time.
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 * To get around this we use the following pre-calculated constants.
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 * If you change CONST_BITS you may want to add appropriate values.
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 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
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 */
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#if CONST_BITS == 13
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#define FIX_0_298631336  ((INT32)  2446)        /* FIX(0.298631336) */
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#define FIX_0_390180644  ((INT32)  3196)        /* FIX(0.390180644) */
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#define FIX_0_541196100  ((INT32)  4433)        /* FIX(0.541196100) */
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#define FIX_0_765366865  ((INT32)  6270)        /* FIX(0.765366865) */
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#define FIX_0_899976223  ((INT32)  7373)        /* FIX(0.899976223) */
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#define FIX_1_175875602  ((INT32)  9633)        /* FIX(1.175875602) */
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#define FIX_1_501321110  ((INT32)  12299)       /* FIX(1.501321110) */
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#define FIX_1_847759065  ((INT32)  15137)       /* FIX(1.847759065) */
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#define FIX_1_961570560  ((INT32)  16069)       /* FIX(1.961570560) */
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#define FIX_2_053119869  ((INT32)  16819)       /* FIX(2.053119869) */
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#define FIX_2_562915447  ((INT32)  20995)       /* FIX(2.562915447) */
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#define FIX_3_072711026  ((INT32)  25172)       /* FIX(3.072711026) */
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#else
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#define FIX_0_298631336  FIX(0.298631336)
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#define FIX_0_390180644  FIX(0.390180644)
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#define FIX_0_541196100  FIX(0.541196100)
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#define FIX_0_765366865  FIX(0.765366865)
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#define FIX_0_899976223  FIX(0.899976223)
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#define FIX_1_175875602  FIX(1.175875602)
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#define FIX_1_501321110  FIX(1.501321110)
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#define FIX_1_847759065  FIX(1.847759065)
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#define FIX_1_961570560  FIX(1.961570560)
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#define FIX_2_053119869  FIX(2.053119869)
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#define FIX_2_562915447  FIX(2.562915447)
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#define FIX_3_072711026  FIX(3.072711026)
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#endif
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/* Descale and correctly round an INT32 value that's scaled by N bits.
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 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
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 * the fudge factor is correct for either sign of X.
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 */
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#define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
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/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
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 * For 8-bit samples with the recommended scaling, all the variable
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 * and constant values involved are no more than 16 bits wide, so a
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 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply;
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 * this provides a useful speedup on many machines.
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 * There is no way to specify a 16x16->32 multiply in portable C, but
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 * some C compilers will do the right thing if you provide the correct
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 * combination of casts.
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 * NB: for 12-bit samples, a full 32-bit multiplication will be needed.
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 */
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#ifdef EIGHT_BIT_SAMPLES
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#ifdef SHORTxSHORT_32           /* may work if 'int' is 32 bits */
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#define MULTIPLY(var,const)  (((INT16) (var)) * ((INT16) (const)))
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#endif
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#ifdef SHORTxLCONST_32          /* known to work with Microsoft C 6.0 */
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#define MULTIPLY(var,const)  (((INT16) (var)) * ((INT32) (const)))
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#endif
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#endif
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#ifndef MULTIPLY                /* default definition */
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#define MULTIPLY(var,const)  ((var) * (const))
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#endif
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/*
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 * Perform the inverse DCT on one block of coefficients.
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 */
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void
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j_rev_dct (DCTBLOCK data)
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{
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  register DCTELEM *dataptr;
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  int i, j;
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  FILE *idctdat;
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  SHIFT_TEMPS
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  dataptr = data;
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  idctdat = fopen("idct-in", "w");
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  for (i = 0; i <= 63; i++) {
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    j = ((INT32)dataptr[i]) & 4095;
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    fprintf(idctdat, "%x\n", j);
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  }
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  fclose(idctdat);
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  system("./idct-verilog > idct-out");
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  idctdat = fopen("idct-out", "r");
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  for (i = 0; i <= 63; i++) {
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    fscanf(idctdat, "%d", &j);
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    dataptr[i] = j;
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  }
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  fclose(idctdat);
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}

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