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/*
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* jfdctflt.c
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*
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* Copyright (C) 1994-1996, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README.ijg
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* file.
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*
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* This file contains a floating-point implementation of the
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* forward DCT (Discrete Cosine Transform).
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*
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* This implementation should be more accurate than either of the integer
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* DCT implementations. However, it may not give the same results on all
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* machines because of differences in roundoff behavior. Speed will depend
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* on the hardware's floating point capacity.
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*
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* A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
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* on each column. Direct algorithms are also available, but they are
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* much more complex and seem not to be any faster when reduced to code.
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*
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* This implementation is based on Arai, Agui, and Nakajima's algorithm for
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* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
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* Japanese, but the algorithm is described in the Pennebaker & Mitchell
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* JPEG textbook (see REFERENCES section in file README.ijg). The following
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* code is based directly on figure 4-8 in P&M.
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* While an 8-point DCT cannot be done in less than 11 multiplies, it is
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* possible to arrange the computation so that many of the multiplies are
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* simple scalings of the final outputs. These multiplies can then be
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* folded into the multiplications or divisions by the JPEG quantization
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* table entries. The AA&N method leaves only 5 multiplies and 29 adds
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* to be done in the DCT itself.
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* The primary disadvantage of this method is that with a fixed-point
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* implementation, accuracy is lost due to imprecise representation of the
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* scaled quantization values. However, that problem does not arise if
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* we use floating point arithmetic.
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*/
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jdct.h" /* Private declarations for DCT subsystem */
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#ifdef DCT_FLOAT_SUPPORTED
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/*
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* This module is specialized to the case DCTSIZE = 8.
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*/
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#if DCTSIZE != 8
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Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
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#endif
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/*
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* Perform the forward DCT on one block of samples.
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*/
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GLOBAL(void)
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jpeg_fdct_float(FAST_FLOAT *data)
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{
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FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
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FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
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FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
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FAST_FLOAT *dataptr;
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int ctr;
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/* Pass 1: process rows. */
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dataptr = data;
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for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) {
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tmp0 = dataptr[0] + dataptr[7];
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tmp7 = dataptr[0] - dataptr[7];
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tmp1 = dataptr[1] + dataptr[6];
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tmp6 = dataptr[1] - dataptr[6];
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tmp2 = dataptr[2] + dataptr[5];
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tmp5 = dataptr[2] - dataptr[5];
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tmp3 = dataptr[3] + dataptr[4];
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tmp4 = dataptr[3] - dataptr[4];
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/* Even part */
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tmp10 = tmp0 + tmp3; /* phase 2 */
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tmp13 = tmp0 - tmp3;
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tmp11 = tmp1 + tmp2;
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tmp12 = tmp1 - tmp2;
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dataptr[0] = tmp10 + tmp11; /* phase 3 */
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dataptr[4] = tmp10 - tmp11;
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z1 = (tmp12 + tmp13) * ((FAST_FLOAT)0.707106781); /* c4 */
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dataptr[2] = tmp13 + z1; /* phase 5 */
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dataptr[6] = tmp13 - z1;
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/* Odd part */
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tmp10 = tmp4 + tmp5; /* phase 2 */
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tmp11 = tmp5 + tmp6;
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tmp12 = tmp6 + tmp7;
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/* The rotator is modified from fig 4-8 to avoid extra negations. */
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z5 = (tmp10 - tmp12) * ((FAST_FLOAT)0.382683433); /* c6 */
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z2 = ((FAST_FLOAT)0.541196100) * tmp10 + z5; /* c2-c6 */
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z4 = ((FAST_FLOAT)1.306562965) * tmp12 + z5; /* c2+c6 */
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z3 = tmp11 * ((FAST_FLOAT)0.707106781); /* c4 */
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z11 = tmp7 + z3; /* phase 5 */
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z13 = tmp7 - z3;
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dataptr[5] = z13 + z2; /* phase 6 */
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dataptr[3] = z13 - z2;
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dataptr[1] = z11 + z4;
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dataptr[7] = z11 - z4;
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dataptr += DCTSIZE; /* advance pointer to next row */
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}
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/* Pass 2: process columns. */
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dataptr = data;
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for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) {
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tmp0 = dataptr[DCTSIZE * 0] + dataptr[DCTSIZE * 7];
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tmp7 = dataptr[DCTSIZE * 0] - dataptr[DCTSIZE * 7];
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tmp1 = dataptr[DCTSIZE * 1] + dataptr[DCTSIZE * 6];
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tmp6 = dataptr[DCTSIZE * 1] - dataptr[DCTSIZE * 6];
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tmp2 = dataptr[DCTSIZE * 2] + dataptr[DCTSIZE * 5];
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tmp5 = dataptr[DCTSIZE * 2] - dataptr[DCTSIZE * 5];
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tmp3 = dataptr[DCTSIZE * 3] + dataptr[DCTSIZE * 4];
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tmp4 = dataptr[DCTSIZE * 3] - dataptr[DCTSIZE * 4];
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/* Even part */
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tmp10 = tmp0 + tmp3; /* phase 2 */
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tmp13 = tmp0 - tmp3;
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tmp11 = tmp1 + tmp2;
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tmp12 = tmp1 - tmp2;
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dataptr[DCTSIZE * 0] = tmp10 + tmp11; /* phase 3 */
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dataptr[DCTSIZE * 4] = tmp10 - tmp11;
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z1 = (tmp12 + tmp13) * ((FAST_FLOAT)0.707106781); /* c4 */
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dataptr[DCTSIZE * 2] = tmp13 + z1; /* phase 5 */
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dataptr[DCTSIZE * 6] = tmp13 - z1;
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/* Odd part */
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tmp10 = tmp4 + tmp5; /* phase 2 */
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tmp11 = tmp5 + tmp6;
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tmp12 = tmp6 + tmp7;
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/* The rotator is modified from fig 4-8 to avoid extra negations. */
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z5 = (tmp10 - tmp12) * ((FAST_FLOAT)0.382683433); /* c6 */
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z2 = ((FAST_FLOAT)0.541196100) * tmp10 + z5; /* c2-c6 */
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z4 = ((FAST_FLOAT)1.306562965) * tmp12 + z5; /* c2+c6 */
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z3 = tmp11 * ((FAST_FLOAT)0.707106781); /* c4 */
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z11 = tmp7 + z3; /* phase 5 */
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z13 = tmp7 - z3;
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dataptr[DCTSIZE * 5] = z13 + z2; /* phase 6 */
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dataptr[DCTSIZE * 3] = z13 - z2;
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dataptr[DCTSIZE * 1] = z11 + z4;
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dataptr[DCTSIZE * 7] = z11 - z4;
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dataptr++; /* advance pointer to next column */
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}
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}
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#endif /* DCT_FLOAT_SUPPORTED */
```