164 lines
5.3 KiB
C++
164 lines
5.3 KiB
C++
// * jfdctflt.c
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// *
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// * Copyright (C) 1994, 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 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). The following code
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// * 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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#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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// * This module is specialized to the case DCTSIZE = 8.
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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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// * Perform the forward DCT on one block of samples.
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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
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