text: /********************************************************************** <BR>
     This file is part of Crack dot Com's free source code release of
     Golgotha. <a href="http://www.crack.com/golgotha_release"> <BR> for
     information about compiling & licensing issues visit this URL</a>
     <PRE> If that doesn't help, contact Jonathan Clark at
     golgotha_source@usa.net (Subject should have "GOLG" in it)
   ***********************************************************************/
  
  /*
   * jidctint.c
   *
   * Copyright (C) 1991-1996, 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 slow-but-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 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 "pch.h"
  #define JPEG_INTERNALS
  #include "loaders/jpg/jinclude.h"
  #include "loaders/jpg/jpeglib.h"
  #include "loaders/jpg/jdct.h"        /* Private declarations for DCT subsystem */
  
  #ifdef DCT_ISLOW_SUPPORTED
  
  
  /*
   * This module is specialized to the case DCTSIZE = 8.
   */
  
  #if DCTSIZE != 8
  Sorry, this code only copes with 8 x8 DCTs.  /* deliberate syntax err */
  		#endif
  
  
  /*
   * 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.
   */
  
  #if BITS_IN_JSAMPLE == 8
  #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
  
  /* 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
  
  
  /* 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.
   * For 12-bit samples, a full 32-bit multiplication will be needed.
   */
  
  #if BITS_IN_JSAMPLE == 8
  #define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
  #else
  #define MULTIPLY(var,const)  ((var) * (const))
  #endif
  
  
  /* Dequantize a coefficient by multiplying it by the multiplier-table
   * entry; produce an int result.  In this module, both inputs and result
   * are 16 bits or less, so either int or short multiply will work.
   */
  
  #define DEQUANTIZE(coef,quantval)  (((ISLOW_MULT_TYPE) (coef)) * (quantval))
  
  
  /*
   * Perform dequantization and inverse DCT on one block of coefficients.
   */
  
  GLOBAL(void)
  jpeg_idct_islow(j_decompress_ptr cinfo, jpeg_component_info * compptr,
  				JCOEFPTR coef_block,
  				JSAMPARRAY output_buf, JDIMENSION output_col)
  {
  	INT32 tmp0, tmp1, tmp2, tmp3;
  	INT32 tmp10, tmp11, tmp12, tmp13;
  	INT32 z1, z2, z3, z4, z5;
  	JCOEFPTR inptr;
  	ISLOW_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
  
  	/* Pass 1: process columns from input, store into work array. */
  	/* Note results are scaled up by sqrt(8) compared to a true IDCT; */
  	/* furthermore, we scale the results by 2**PASS1_BITS. */
  
  	inptr = coef_block;
  
  	quantptr = (ISLOW_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] | inptr[DCTSIZE*2] | inptr[DCTSIZE*3] |
  			 inptr[DCTSIZE*4] | inptr[DCTSIZE*5] | inptr[DCTSIZE*6] |
  			 inptr[DCTSIZE*7]) == 0)
  		{
  			/* AC terms all zero */
  			int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
  
  			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: reverse the even part of the forward DCT. */
  		/* The rotator is sqrt(2)*c(-6). */
  
  		z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
  		z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
  
  		z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
  		tmp2 = z1 + MULTIPLY(z3, -FIX_1_847759065);
  		tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
  
  		z2 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
  		z3 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
  
  		tmp0 = (z2 + z3) << CONST_BITS;
  		tmp1 = (z2 - z3) << CONST_BITS;
  
  		tmp10 = tmp0 + tmp3;
  		tmp13 = tmp0 - tmp3;
  		tmp11 = tmp1 + tmp2;
  		tmp12 = tmp1 - tmp2;
  
  		/* Odd part per figure 8; the matrix is unitary and hence its
  		 * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
  		 */
  
  		tmp0 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
  		tmp1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
  		tmp2 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
  		tmp3 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
  
  		z1 = tmp0 + tmp3;
  		z2 = tmp1 + tmp2;
  		z3 = tmp0 + tmp2;
  		z4 = tmp1 + tmp3;
  		z5 = MULTIPLY(z3 + z4, FIX_1_175875602);/* sqrt(2) * c3 */
  
  		tmp0 = MULTIPLY(tmp0, FIX_0_298631336);/* sqrt(2) * (-c1+c3+c5-c7) */
  		tmp1 = MULTIPLY(tmp1, FIX_2_053119869);/* sqrt(2) * ( c1+c3-c5+c7) */
  		tmp2 = MULTIPLY(tmp2, FIX_3_072711026);/* sqrt(2) * ( c1+c3+c5-c7) */
  		tmp3 = MULTIPLY(tmp3, FIX_1_501321110);/* sqrt(2) * ( c1+c3-c5-c7) */
  		z1 = MULTIPLY(z1, -FIX_0_899976223);/* sqrt(2) * (c7-c3) */
  		z2 = MULTIPLY(z2, -FIX_2_562915447);/* sqrt(2) * (-c1-c3) */
  		z3 = MULTIPLY(z3, -FIX_1_961570560);/* sqrt(2) * (-c3-c5) */
  		z4 = MULTIPLY(z4, -FIX_0_390180644);/* sqrt(2) * (c5-c3) */
  
  		z3 += z5;
  		z4 += z5;
  
  		tmp0 += z1 + z3;
  		tmp1 += z2 + z4;
  		tmp2 += z2 + z3;
  		tmp3 += z1 + z4;
  
  		/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
  
  		wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
  		wsptr[DCTSIZE*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);
  
  		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] | wsptr[2] | wsptr[3] | wsptr[4] | wsptr[5] | wsptr[6] |
  			 wsptr[7]) == 0)
  		{
  			/* AC terms all zero */
  			JSAMPLE dcval = range_limit[(int) DESCALE((INT32) 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: reverse the even part of the forward DCT. */
  		/* The rotator is sqrt(2)*c(-6). */
  
  		z2 = (INT32) wsptr[2];
  		z3 = (INT32) wsptr[6];
  
  		z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
  		tmp2 = z1 + MULTIPLY(z3, -FIX_1_847759065);
  		tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
  
  		tmp0 = ((INT32) wsptr[0] + (INT32) wsptr[4]) << CONST_BITS;
  		tmp1 = ((INT32) wsptr[0] - (INT32) wsptr[4]) << CONST_BITS;
  
  		tmp10 = tmp0 + tmp3;
  		tmp13 = tmp0 - tmp3;
  		tmp11 = tmp1 + tmp2;
  		tmp12 = tmp1 - tmp2;
  
  		/* Odd part per figure 8; the matrix is unitary and hence its
  		 * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
  		 */
  
  		tmp0 = (INT32) wsptr[7];
  		tmp1 = (INT32) wsptr[5];
  		tmp2 = (INT32) wsptr[3];
  		tmp3 = (INT32) wsptr[1];
  
  		z1 = tmp0 + tmp3;
  		z2 = tmp1 + tmp2;
  		z3 = tmp0 + tmp2;
  		z4 = tmp1 + tmp3;
  		z5 = MULTIPLY(z3 + z4, FIX_1_175875602);/* sqrt(2) * c3 */
  
  		tmp0 = MULTIPLY(tmp0, FIX_0_298631336);/* sqrt(2) * (-c1+c3+c5-c7) */
  		tmp1 = MULTIPLY(tmp1, FIX_2_053119869);/* sqrt(2) * ( c1+c3-c5+c7) */
  		tmp2 = MULTIPLY(tmp2, FIX_3_072711026);/* sqrt(2) * ( c1+c3+c5-c7) */
  		tmp3 = MULTIPLY(tmp3, FIX_1_501321110);/* sqrt(2) * ( c1+c3-c5-c7) */
  		z1 = MULTIPLY(z1, -FIX_0_899976223);/* sqrt(2) * (c7-c3) */
  		z2 = MULTIPLY(z2, -FIX_2_562915447);/* sqrt(2) * (-c1-c3) */
  		z3 = MULTIPLY(z3, -FIX_1_961570560);/* sqrt(2) * (-c3-c5) */
  		z4 = MULTIPLY(z4, -FIX_0_390180644);/* sqrt(2) * (c5-c3) */
  
  		z3 += z5;
  		z4 += z5;
  
  		tmp0 += z1 + z3;
  		tmp1 += z2 + z4;
  		tmp2 += z2 + z3;
  		tmp3 += z1 + z4;
  
  		/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
  
  		outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  		outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0,
  											  CONST_BITS+PASS1_BITS+3)
  								& RANGE_MASK];
  
  		wsptr += DCTSIZE;   /* advance pointer to next row */
  	}
  }
  
  #endif /* DCT_ISLOW_SUPPORTED */
  