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| 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[DCTSIZE*0] + dataptr[DCTSIZE*7]; | |
| 122 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; | |
| 123 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; | |
| 124 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; | |
| 125 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; | |
| 126 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; | |
| 127 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; | |
| 128 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; | |
| 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[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ | |
| 138 dataptr[DCTSIZE*4] = tmp10 - tmp11; | |
| 139 | |
| 140 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ | |
| 141 dataptr[DCTSIZE*2] = 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[DCTSIZE*5] = 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 */ | |
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