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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 */ |