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/* idct.c, inverse fast discrete cosine transform                           */

/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */

/*

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 *

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 *

 * The MPEG Software Simulation Group does not represent or warrant that the

 * programs furnished hereunder are free of infringement of any third-party

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/**********************************************************/

/* inverse two dimensional DCT, Chen-Wang algorithm       */

/* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984)             */

/* 32-bit integer arithmetic (8 bit coefficients)         */

/* 11 mults, 29 adds per DCT                              */

/*                                      sE, 18.8.91       */

/**********************************************************/

/* coefficients extended to 12 bit for IEEE1180-1990      */

/* compliance                           sE,  2.1.94       */

/**********************************************************/

/* this code assumes >> to be a two's-complement arithmetic */

/* right shift: (-2)>>1 == -1 , (-3)>>1 == -2               */

#include "config.h"

#define W1 2841 /* 2048*sqrt(2)*cos(1*pi/16) */

#define W2 2676 /* 2048*sqrt(2)*cos(2*pi/16) */

#define W3 2408 /* 2048*sqrt(2)*cos(3*pi/16) */

#define W5 1609 /* 2048*sqrt(2)*cos(5*pi/16) */

#define W6 1108 /* 2048*sqrt(2)*cos(6*pi/16) */

#define W7 565  /* 2048*sqrt(2)*cos(7*pi/16) */

/* global declarations */

void Initialize_Fast_IDCT _ANSI_ARGS_((void));

void Fast_IDCT _ANSI_ARGS_((short *block));

/* private data */

static short iclip[1024]; /* clipping table */

static short *iclp;

/* private prototypes */

static void idctrow _ANSI_ARGS_((short *blk));

static void idctcol _ANSI_ARGS_((short *blk));

/* row (horizontal) IDCT

 *

 *           7                       pi         1

 * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l )

 *          l=0                      8          2

 *

 * where: c[0]    = 128

 *        c[1..7] = 128*sqrt(2)

 */

static void idctrow(blk)

short *blk;

{

  int x0, x1, x2, x3, x4, x5, x6, x7, x8;

  /* shortcut */

  if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) |

        (x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3])))

  {

    blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3;

    return;

  }

  x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */

  /* first stage */

  x8 = W7*(x4+x5);

  x4 = x8 + (W1-W7)*x4;

  x5 = x8 - (W1+W7)*x5;

  x8 = W3*(x6+x7);

  x6 = x8 - (W3-W5)*x6;

  x7 = x8 - (W3+W5)*x7;

  /* second stage */

  x8 = x0 + x1;

  x0 -= x1;

  x1 = W6*(x3+x2);

  x2 = x1 - (W2+W6)*x2;

  x3 = x1 + (W2-W6)*x3;

  x1 = x4 + x6;

  x4 -= x6;

  x6 = x5 + x7;

  x5 -= x7;

  /* third stage */

  x7 = x8 + x3;

  x8 -= x3;

  x3 = x0 + x2;

  x0 -= x2;

  x2 = (181*(x4+x5)+128)>>8;

  x4 = (181*(x4-x5)+128)>>8;

  /* fourth stage */

  blk[0] = (x7+x1)>>8;

  blk[1] = (x3+x2)>>8;

  blk[2] = (x0+x4)>>8;

  blk[3] = (x8+x6)>>8;

  blk[4] = (x8-x6)>>8;

  blk[5] = (x0-x4)>>8;

  blk[6] = (x3-x2)>>8;

  blk[7] = (x7-x1)>>8;

}

/* column (vertical) IDCT

 *

 *             7                         pi         1

 * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l )

 *            l=0                        8          2

 *

 * where: c[0]    = 1/1024

 *        c[1..7] = (1/1024)*sqrt(2)

 */

static void idctcol(blk)

short *blk;

{

  int x0, x1, x2, x3, x4, x5, x6, x7, x8;

  /* shortcut */

  if (!((x1 = (blk[8*4]<<8)) | (x2 = blk[8*6]) | (x3 = blk[8*2]) |

        (x4 = blk[8*1]) | (x5 = blk[8*7]) | (x6 = blk[8*5]) | (x7 = blk[8*3])))

  {

    blk[8*0]=blk[8*1]=blk[8*2]=blk[8*3]=blk[8*4]=blk[8*5]=blk[8*6]=blk[8*7]=

      iclp[(blk[8*0]+32)>>6];

    return;

  }

  x0 = (blk[8*0]<<8) + 8192;

  /* first stage */

  x8 = W7*(x4+x5) + 4;

  x4 = (x8+(W1-W7)*x4)>>3;

  x5 = (x8-(W1+W7)*x5)>>3;

  x8 = W3*(x6+x7) + 4;

  x6 = (x8-(W3-W5)*x6)>>3;

  x7 = (x8-(W3+W5)*x7)>>3;

  /* second stage */

  x8 = x0 + x1;

  x0 -= x1;

  x1 = W6*(x3+x2) + 4;

  x2 = (x1-(W2+W6)*x2)>>3;

  x3 = (x1+(W2-W6)*x3)>>3;

  x1 = x4 + x6;

  x4 -= x6;

  x6 = x5 + x7;

  x5 -= x7;

  /* third stage */

  x7 = x8 + x3;

  x8 -= x3;

  x3 = x0 + x2;

  x0 -= x2;

  x2 = (181*(x4+x5)+128)>>8;

  x4 = (181*(x4-x5)+128)>>8;

  /* fourth stage */

  blk[8*0] = iclp[(x7+x1)>>14];

  blk[8*1] = iclp[(x3+x2)>>14];

  blk[8*2] = iclp[(x0+x4)>>14];

  blk[8*3] = iclp[(x8+x6)>>14];

  blk[8*4] = iclp[(x8-x6)>>14];

  blk[8*5] = iclp[(x0-x4)>>14];

  blk[8*6] = iclp[(x3-x2)>>14];

  blk[8*7] = iclp[(x7-x1)>>14];

}

/* two dimensional inverse discrete cosine transform */

void Fast_IDCT(block)

short *block;

{

  int i;

  for (i=0; i<8; i++)

    idctrow(block+8*i);

  for (i=0; i<8; i++)

    idctcol(block+i);

}

void Initialize_Fast_IDCT()

{

  int i;

  iclp = iclip+512;

  for (i= -512; i<512; i++)

    iclp[i] = (i<-256) ? -256 : ((i>255) ? 255 : i);

}