/*

* jfdctflt.c

*

* Copyright (C) 1994-1996, Thomas G. Lane.

* Modified 2003-2017 by Guido Vollbeding.

* 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 DCT blocks. /* deliberate syntax err */

#endif

/*

* Perform the forward DCT on one block of samples.

*

* cK represents cos(K*pi/16).

*/

GLOBAL(void)

jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col)

{

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;

JSAMPROW elemptr;

int ctr;

/* Pass 1: process rows. */

dataptr = data;

for (ctr = 0; ctr < DCTSIZE; ctr++) {

elemptr = sample_data[ctr] + start_col;

/* Load data into workspace */

tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]));

tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]));

tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]));

tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]));

tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]));

tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]));

tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]));

tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]));

/* Even part */

tmp10 = tmp0 + tmp3; /* phase 2 */

tmp13 = tmp0 - tmp3;

tmp11 = tmp1 + tmp2;

tmp12 = tmp1 - tmp2;

/* Apply unsigned->signed conversion. */

dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* 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 */