src/jpeg/jfdctflt.c

/*
 * jfdctflt.c
 *
 * Copyright (C) 1994-1996, 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 floating-point implementation of the
 * forward DCT (Discrete Cosine Transform).
 *
 * This implementation should be more accurate than either of the integer
 * DCT 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 DCT can be done by 1-D DCT on each row followed by 1-D DCT
 * on each column.  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


/*
 * Perform the forward DCT on one block of samples.
 */

GLOBAL(void)
jpeg_fdct_float (FAST_FLOAT * data)
{
  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
  FAST_FLOAT *dataptr;
  int ctr;

  /* Pass 1: process rows. */

  dataptr = data;
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
    tmp0 = dataptr[0] + dataptr[7];
    tmp7 = dataptr[0] - dataptr[7];
    tmp1 = dataptr[1] + dataptr[6];
    tmp6 = dataptr[1] - dataptr[6];
    tmp2 = dataptr[2] + dataptr[5];
    tmp5 = dataptr[2] - dataptr[5];
    tmp3 = dataptr[3] + dataptr[4];
    tmp4 = dataptr[3] - dataptr[4];

    /* Even part */

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

    dataptr[0] = tmp10 + tmp11; /* phase 3 */
    dataptr[4] = tmp10 - tmp11;

    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
    dataptr[2] = tmp13 + z1;	/* phase 5 */
    dataptr[6] = tmp13 - z1;

    /* Odd part */

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

    /* The rotator is modified from fig 4-8 to avoid extra negations. */
    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */

    z11 = tmp7 + z3;		/* phase 5 */
    z13 = tmp7 - z3;

    dataptr[5] = z13 + z2;	/* phase 6 */
    dataptr[3] = z13 - z2;
    dataptr[1] = z11 + z4;
    dataptr[7] = z11 - z4;

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

  /* Pass 2: process columns. */

  dataptr = data;
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];

    /* Even part */

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

    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
    dataptr[DCTSIZE*4] = tmp10 - tmp11;

    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
    dataptr[DCTSIZE*6] = tmp13 - z1;

    /* Odd part */

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

    /* The rotator is modified from fig 4-8 to avoid extra negations. */
    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */

    z11 = tmp7 + z3;		/* phase 5 */
    z13 = tmp7 - z3;

    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
    dataptr[DCTSIZE*3] = z13 - z2;
    dataptr[DCTSIZE*1] = z11 + z4;
    dataptr[DCTSIZE*7] = z11 - z4;

    dataptr++;			/* advance pointer to next column */
  }
}

#endif /* DCT_FLOAT_SUPPORTED */
Commit	Line	Data
	1	/*
	2	* jfdctflt.c
	3	*
	4	* Copyright (C) 1994-1996, Thomas G. Lane.
	5	* This file is part of the Independent JPEG Group's software.
	6	* For conditions of distribution and use, see the accompanying README file.
	7	*
	8	* This file contains a floating-point implementation of the
	9	* forward DCT (Discrete Cosine Transform).
	10	*
	11	* This implementation should be more accurate than either of the integer
	12	* DCT implementations. However, it may not give the same results on all
	13	* machines because of differences in roundoff behavior. Speed will depend
	14	* on the hardware's floating point capacity.
	15	*
	16	* A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
	17	* on each column. Direct algorithms are also available, but they are
	18	* much more complex and seem not to be any faster when reduced to code.
	19	*
	20	* This implementation is based on Arai, Agui, and Nakajima's algorithm for
	21	* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
	22	* Japanese, but the algorithm is described in the Pennebaker & Mitchell
	23	* JPEG textbook (see REFERENCES section in file README). The following code
	24	* is based directly on figure 4-8 in P&M.
	25	* While an 8-point DCT cannot be done in less than 11 multiplies, it is
	26	* possible to arrange the computation so that many of the multiplies are
	27	* simple scalings of the final outputs. These multiplies can then be
	28	* folded into the multiplications or divisions by the JPEG quantization
	29	* table entries. The AA&N method leaves only 5 multiplies and 29 adds
	30	* to be done in the DCT itself.
	31	* The primary disadvantage of this method is that with a fixed-point
	32	* implementation, accuracy is lost due to imprecise representation of the
	33	* scaled quantization values. However, that problem does not arise if
	34	* we use floating point arithmetic.
	35	*/
	36
	37	#define JPEG_INTERNALS
	38	#include "jinclude.h"
	39	#include "jpeglib.h"
	40	#include "jdct.h" /* Private declarations for DCT subsystem */
	41
	42	#ifdef DCT_FLOAT_SUPPORTED
	43
	44
	45	/*
	46	* This module is specialized to the case DCTSIZE = 8.
	47	*/
	48
	49	#if DCTSIZE != 8
	50	Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
	51	#endif
	52
	53
	54	/*
	55	* Perform the forward DCT on one block of samples.
	56	*/
	57
	58	GLOBAL(void)
	59	jpeg_fdct_float (FAST_FLOAT * data)
	60	{
	61	FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
	62	FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
	63	FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
	64	FAST_FLOAT *dataptr;
	65	int ctr;
	66
	67	/* Pass 1: process rows. */
	68
	69	dataptr = data;
	70	for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
	71	tmp0 = dataptr[0] + dataptr[7];
	72	tmp7 = dataptr[0] - dataptr[7];
	73	tmp1 = dataptr[1] + dataptr[6];
	74	tmp6 = dataptr[1] - dataptr[6];
	75	tmp2 = dataptr[2] + dataptr[5];
	76	tmp5 = dataptr[2] - dataptr[5];
	77	tmp3 = dataptr[3] + dataptr[4];
	78	tmp4 = dataptr[3] - dataptr[4];
	79
	80	/* Even part */
	81
	82	tmp10 = tmp0 + tmp3; /* phase 2 */
	83	tmp13 = tmp0 - tmp3;
	84	tmp11 = tmp1 + tmp2;
	85	tmp12 = tmp1 - tmp2;
	86
	87	dataptr[0] = tmp10 + tmp11; /* phase 3 */
	88	dataptr[4] = tmp10 - tmp11;
	89
	90	z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
	91	dataptr[2] = tmp13 + z1; /* phase 5 */
	92	dataptr[6] = tmp13 - z1;
	93
	94	/* Odd part */
	95
	96	tmp10 = tmp4 + tmp5; /* phase 2 */
	97	tmp11 = tmp5 + tmp6;
	98	tmp12 = tmp6 + tmp7;
	99
	100	/* The rotator is modified from fig 4-8 to avoid extra negations. */
	101	z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
	102	z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
	103	z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
	104	z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
	105
	106	z11 = tmp7 + z3; /* phase 5 */
	107	z13 = tmp7 - z3;
	108
	109	dataptr[5] = z13 + z2; /* phase 6 */
	110	dataptr[3] = z13 - z2;
	111	dataptr[1] = z11 + z4;
	112	dataptr[7] = z11 - z4;
	113
	114	dataptr += DCTSIZE; /* advance pointer to next row */
	115	}
	116
	117	/* Pass 2: process columns. */
	118
	119	dataptr = data;
	120	for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
	121	tmp0 = dataptr[DCTSIZE0] + dataptr[DCTSIZE7];
	122	tmp7 = dataptr[DCTSIZE0] - dataptr[DCTSIZE7];
	123	tmp1 = dataptr[DCTSIZE1] + dataptr[DCTSIZE6];
	124	tmp6 = dataptr[DCTSIZE1] - dataptr[DCTSIZE6];
	125	tmp2 = dataptr[DCTSIZE2] + dataptr[DCTSIZE5];
	126	tmp5 = dataptr[DCTSIZE2] - dataptr[DCTSIZE5];
	127	tmp3 = dataptr[DCTSIZE3] + dataptr[DCTSIZE4];
	128	tmp4 = dataptr[DCTSIZE3] - dataptr[DCTSIZE4];
	129
	130	/* Even part */
	131
	132	tmp10 = tmp0 + tmp3; /* phase 2 */
	133	tmp13 = tmp0 - tmp3;
	134	tmp11 = tmp1 + tmp2;
	135	tmp12 = tmp1 - tmp2;
	136
	137	dataptr[DCTSIZE0] = tmp10 + tmp11; / phase 3 */
	138	dataptr[DCTSIZE*4] = tmp10 - tmp11;
	139
	140	z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
	141	dataptr[DCTSIZE2] = tmp13 + z1; / phase 5 */
	142	dataptr[DCTSIZE*6] = tmp13 - z1;
	143
	144	/* Odd part */
	145
	146	tmp10 = tmp4 + tmp5; /* phase 2 */
	147	tmp11 = tmp5 + tmp6;
	148	tmp12 = tmp6 + tmp7;
	149
	150	/* The rotator is modified from fig 4-8 to avoid extra negations. */
	151	z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
	152	z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
	153	z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
	154	z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
	155
	156	z11 = tmp7 + z3; /* phase 5 */
	157	z13 = tmp7 - z3;
	158
	159	dataptr[DCTSIZE5] = z13 + z2; / phase 6 */
	160	dataptr[DCTSIZE*3] = z13 - z2;
	161	dataptr[DCTSIZE*1] = z11 + z4;
	162	dataptr[DCTSIZE*7] = z11 - z4;
	163
	164	dataptr++; /* advance pointer to next column */
	165	}
	166	}
	167
	168	#endif /* DCT_FLOAT_SUPPORTED */