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