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plt-scheme  4.2.1
Defines | Functions
jidctint.c File Reference
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"

Go to the source code of this file.

Defines

#define JPEG_INTERNALS
#define CONST_BITS   13
#define PASS1_BITS   2
#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) */
#define MULTIPLY(var, const)   MULTIPLY16C16(var,const)
#define DEQUANTIZE(coef, quantval)   (((ISLOW_MULT_TYPE) (coef)) * (quantval))

Functions

 jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info *compptr, JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)

Define Documentation

#define CONST_BITS   13

Definition at line 78 of file jidctint.c.

#define DEQUANTIZE (   coef,
  quantval 
)    (((ISLOW_MULT_TYPE) (coef)) * (quantval))

Definition at line 140 of file jidctint.c.

#define FIX_0_298631336   ((INT32) 2446) /* FIX(0.298631336) */

Definition at line 93 of file jidctint.c.

#define FIX_0_390180644   ((INT32) 3196) /* FIX(0.390180644) */

Definition at line 94 of file jidctint.c.

#define FIX_0_541196100   ((INT32) 4433) /* FIX(0.541196100) */

Definition at line 95 of file jidctint.c.

#define FIX_0_765366865   ((INT32) 6270) /* FIX(0.765366865) */

Definition at line 96 of file jidctint.c.

#define FIX_0_899976223   ((INT32) 7373) /* FIX(0.899976223) */

Definition at line 97 of file jidctint.c.

#define FIX_1_175875602   ((INT32) 9633) /* FIX(1.175875602) */

Definition at line 98 of file jidctint.c.

#define FIX_1_501321110   ((INT32) 12299) /* FIX(1.501321110) */

Definition at line 99 of file jidctint.c.

#define FIX_1_847759065   ((INT32) 15137) /* FIX(1.847759065) */

Definition at line 100 of file jidctint.c.

#define FIX_1_961570560   ((INT32) 16069) /* FIX(1.961570560) */

Definition at line 101 of file jidctint.c.

#define FIX_2_053119869   ((INT32) 16819) /* FIX(2.053119869) */

Definition at line 102 of file jidctint.c.

#define FIX_2_562915447   ((INT32) 20995) /* FIX(2.562915447) */

Definition at line 103 of file jidctint.c.

#define FIX_3_072711026   ((INT32) 25172) /* FIX(3.072711026) */

Definition at line 104 of file jidctint.c.

#define JPEG_INTERNALS

Definition at line 28 of file jidctint.c.

#define MULTIPLY (   var,
  const 
)    MULTIPLY16C16(var,const)

Definition at line 129 of file jidctint.c.

#define PASS1_BITS   2

Definition at line 79 of file jidctint.c.


Function Documentation

jpeg_idct_islow ( j_decompress_ptr  cinfo,
jpeg_component_info compptr,
JCOEFPTR  coef_block,
JSAMPARRAY  output_buf,
JDIMENSION  output_col 
)

Definition at line 148 of file jidctint.c.

{
  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] == 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 = 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] == 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[(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 */
  }
}

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