src/third_party/libjpeg/jidctflt.c - cobalt - Git at Google

 /*
  * jidctflt.c
  *
  * Copyright (C) 1994-1998, 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 floating-point implementation of the
  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
  * must also perform dequantization of the input coefficients.
  *
  * This implementation should be more accurate than either of the integer
  * IDCT implementations.  However, it may not give the same results on all
  * machines because of differences in roundoff behavior.  Speed will depend
  * on the hardware's floating point capacity.
  *
  * 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 Arai, Agui, and Nakajima's algorithm for
  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  * JPEG textbook (see REFERENCES section in file README).  The following code
  * is based directly on figure 4-8 in P&M.
  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  * possible to arrange the computation so that many of the multiplies are
  * simple scalings of the final outputs.  These multiplies can then be
  * folded into the multiplications or divisions by the JPEG quantization
  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  * to be done in the DCT itself.
  * The primary disadvantage of this method is that with a fixed-point
  * implementation, accuracy is lost due to imprecise representation of the
  * scaled quantization values.  However, that problem does not arise if
  * we use floating point arithmetic.
  */

 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"
 #include "jdct.h"		/* Private declarations for DCT subsystem */

 #ifdef DCT_FLOAT_SUPPORTED


 /*
  * This module is specialized to the case DCTSIZE = 8.
  */

 #if DCTSIZE != 8
   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
 #endif


 /* Dequantize a coefficient by multiplying it by the multiplier-table
  * entry; produce a float result.
  */

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


 /*
  * Perform dequantization and inverse DCT on one block of coefficients.
  */

 GLOBAL(void)
 jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
 		 JCOEFPTR coef_block,
 		 JSAMPARRAY output_buf, JDIMENSION output_col)
 {
   FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
   FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
   FAST_FLOAT z5, z10, z11, z12, z13;
   JCOEFPTR inptr;
   FLOAT_MULT_TYPE * quantptr;
   FAST_FLOAT * wsptr;
   JSAMPROW outptr;
   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
   int ctr;
   FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
   SHIFT_TEMPS

   /* Pass 1: process columns from input, store into work array. */

   inptr = coef_block;
   quantptr = (FLOAT_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 */
       FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);

       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 */

     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);

     tmp10 = tmp0 + tmp2;	/* phase 3 */
     tmp11 = tmp0 - tmp2;

     tmp13 = tmp1 + tmp3;	/* phases 5-3 */
     tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */

     tmp0 = tmp10 + tmp13;	/* phase 2 */
     tmp3 = tmp10 - tmp13;
     tmp1 = tmp11 + tmp12;
     tmp2 = tmp11 - tmp12;

     /* Odd part */

     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);

     z13 = tmp6 + tmp5;		/* phase 6 */
     z10 = tmp6 - tmp5;
     z11 = tmp4 + tmp7;
     z12 = tmp4 - tmp7;

     tmp7 = z11 + z13;		/* phase 5 */
     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */

     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

     tmp6 = tmp12 - tmp7;	/* phase 2 */
     tmp5 = tmp11 - tmp6;
     tmp4 = tmp10 + tmp5;

     wsptr[DCTSIZE*0] = tmp0 + tmp7;
     wsptr[DCTSIZE*7] = tmp0 - tmp7;
     wsptr[DCTSIZE*1] = tmp1 + tmp6;
     wsptr[DCTSIZE*6] = tmp1 - tmp6;
     wsptr[DCTSIZE*2] = tmp2 + tmp5;
     wsptr[DCTSIZE*5] = tmp2 - tmp5;
     wsptr[DCTSIZE*4] = tmp3 + tmp4;
     wsptr[DCTSIZE*3] = tmp3 - tmp4;

     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. */

   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).
      * And testing floats for zero is relatively expensive, so we don't bother.
      */

     /* Even part */

     tmp10 = wsptr[0] + wsptr[4];
     tmp11 = wsptr[0] - wsptr[4];

     tmp13 = wsptr[2] + wsptr[6];
     tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;

     tmp0 = tmp10 + tmp13;
     tmp3 = tmp10 - tmp13;
     tmp1 = tmp11 + tmp12;
     tmp2 = tmp11 - tmp12;

     /* Odd part */

     z13 = wsptr[5] + wsptr[3];
     z10 = wsptr[5] - wsptr[3];
     z11 = wsptr[1] + wsptr[7];
     z12 = wsptr[1] - wsptr[7];

     tmp7 = z11 + z13;
     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);

     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

     tmp6 = tmp12 - tmp7;
     tmp5 = tmp11 - tmp6;
     tmp4 = tmp10 + tmp5;

     /* Final output stage: scale down by a factor of 8 and range-limit */

     outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
 			    & RANGE_MASK];
     outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
 			    & RANGE_MASK];
     outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
 			    & RANGE_MASK];
     outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
 			    & RANGE_MASK];
     outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
 			    & RANGE_MASK];
     outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
 			    & RANGE_MASK];
     outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
 			    & RANGE_MASK];
     outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
 			    & RANGE_MASK];

     wsptr += DCTSIZE;		/* advance pointer to next row */
   }
 }

 #endif /* DCT_FLOAT_SUPPORTED */
	/*
	* jidctflt.c
	*
	* Copyright (C) 1994-1998, 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 floating-point implementation of the
	* inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
	* must also perform dequantization of the input coefficients.
	*
	* This implementation should be more accurate than either of the integer
	* IDCT implementations. However, it may not give the same results on all
	* machines because of differences in roundoff behavior. Speed will depend
	* on the hardware's floating point capacity.
	*
	* 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 Arai, Agui, and Nakajima's algorithm for
	* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
	* Japanese, but the algorithm is described in the Pennebaker & Mitchell
	* JPEG textbook (see REFERENCES section in file README). The following code
	* is based directly on figure 4-8 in P&M.
	* While an 8-point DCT cannot be done in less than 11 multiplies, it is
	* possible to arrange the computation so that many of the multiplies are
	* simple scalings of the final outputs. These multiplies can then be
	* folded into the multiplications or divisions by the JPEG quantization
	* table entries. The AA&N method leaves only 5 multiplies and 29 adds
	* to be done in the DCT itself.
	* The primary disadvantage of this method is that with a fixed-point
	* implementation, accuracy is lost due to imprecise representation of the
	* scaled quantization values. However, that problem does not arise if
	* we use floating point arithmetic.
	*/

	#define JPEG_INTERNALS
	#include "jinclude.h"
	#include "jpeglib.h"
	#include "jdct.h" /* Private declarations for DCT subsystem */

	#ifdef DCT_FLOAT_SUPPORTED


	/*
	* This module is specialized to the case DCTSIZE = 8.
	*/

	#if DCTSIZE != 8
	Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
	#endif


	/* Dequantize a coefficient by multiplying it by the multiplier-table
	* entry; produce a float result.
	*/

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


	/*
	* Perform dequantization and inverse DCT on one block of coefficients.
	*/

	GLOBAL(void)
	jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
	JCOEFPTR coef_block,
	JSAMPARRAY output_buf, JDIMENSION output_col)
	{
	FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
	FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
	FAST_FLOAT z5, z10, z11, z12, z13;
	JCOEFPTR inptr;
	FLOAT_MULT_TYPE * quantptr;
	FAST_FLOAT * wsptr;
	JSAMPROW outptr;
	JSAMPLE *range_limit = IDCT_range_limit(cinfo);
	int ctr;
	FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
	SHIFT_TEMPS

	/* Pass 1: process columns from input, store into work array. */

	inptr = coef_block;
	quantptr = (FLOAT_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[DCTSIZE1] == 0 && inptr[DCTSIZE2] == 0 &&
	inptr[DCTSIZE3] == 0 && inptr[DCTSIZE4] == 0 &&
	inptr[DCTSIZE5] == 0 && inptr[DCTSIZE6] == 0 &&
	inptr[DCTSIZE*7] == 0) {
	/* AC terms all zero */
	FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE0], quantptr[DCTSIZE0]);

	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 */

	tmp0 = DEQUANTIZE(inptr[DCTSIZE0], quantptr[DCTSIZE0]);
	tmp1 = DEQUANTIZE(inptr[DCTSIZE2], quantptr[DCTSIZE2]);
	tmp2 = DEQUANTIZE(inptr[DCTSIZE4], quantptr[DCTSIZE4]);
	tmp3 = DEQUANTIZE(inptr[DCTSIZE6], quantptr[DCTSIZE6]);

	tmp10 = tmp0 + tmp2; /* phase 3 */
	tmp11 = tmp0 - tmp2;

	tmp13 = tmp1 + tmp3; /* phases 5-3 */
	tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2c4 /

	tmp0 = tmp10 + tmp13; /* phase 2 */
	tmp3 = tmp10 - tmp13;
	tmp1 = tmp11 + tmp12;
	tmp2 = tmp11 - tmp12;

	/* Odd part */

	tmp4 = DEQUANTIZE(inptr[DCTSIZE1], quantptr[DCTSIZE1]);
	tmp5 = DEQUANTIZE(inptr[DCTSIZE3], quantptr[DCTSIZE3]);
	tmp6 = DEQUANTIZE(inptr[DCTSIZE5], quantptr[DCTSIZE5]);
	tmp7 = DEQUANTIZE(inptr[DCTSIZE7], quantptr[DCTSIZE7]);

	z13 = tmp6 + tmp5; /* phase 6 */
	z10 = tmp6 - tmp5;
	z11 = tmp4 + tmp7;
	z12 = tmp4 - tmp7;

	tmp7 = z11 + z13; /* phase 5 */
	tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2c4 /

	z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2c2 /
	tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2(c2-c6) /
	tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2(c2+c6) /

	tmp6 = tmp12 - tmp7; /* phase 2 */
	tmp5 = tmp11 - tmp6;
	tmp4 = tmp10 + tmp5;

	wsptr[DCTSIZE*0] = tmp0 + tmp7;
	wsptr[DCTSIZE*7] = tmp0 - tmp7;
	wsptr[DCTSIZE*1] = tmp1 + tmp6;
	wsptr[DCTSIZE*6] = tmp1 - tmp6;
	wsptr[DCTSIZE*2] = tmp2 + tmp5;
	wsptr[DCTSIZE*5] = tmp2 - tmp5;
	wsptr[DCTSIZE*4] = tmp3 + tmp4;
	wsptr[DCTSIZE*3] = tmp3 - tmp4;

	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. /

	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).
	* And testing floats for zero is relatively expensive, so we don't bother.
	*/

	/* Even part */

	tmp10 = wsptr[0] + wsptr[4];
	tmp11 = wsptr[0] - wsptr[4];

	tmp13 = wsptr[2] + wsptr[6];
	tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;

	tmp0 = tmp10 + tmp13;
	tmp3 = tmp10 - tmp13;
	tmp1 = tmp11 + tmp12;
	tmp2 = tmp11 - tmp12;

	/* Odd part */

	z13 = wsptr[5] + wsptr[3];
	z10 = wsptr[5] - wsptr[3];
	z11 = wsptr[1] + wsptr[7];
	z12 = wsptr[1] - wsptr[7];

	tmp7 = z11 + z13;
	tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);

	z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2c2 /
	tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2(c2-c6) /
	tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2(c2+c6) /

	tmp6 = tmp12 - tmp7;
	tmp5 = tmp11 - tmp6;
	tmp4 = tmp10 + tmp5;

	/* Final output stage: scale down by a factor of 8 and range-limit */

	outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
	& RANGE_MASK];
	outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
	& RANGE_MASK];
	outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
	& RANGE_MASK];
	outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
	& RANGE_MASK];
	outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
	& RANGE_MASK];
	outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
	& RANGE_MASK];
	outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
	& RANGE_MASK];
	outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
	& RANGE_MASK];

	wsptr += DCTSIZE; /* advance pointer to next row */
	}
	}

	#endif /* DCT_FLOAT_SUPPORTED */