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1 /* |
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2 * jidctred.c |
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3 * |
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4 * Copyright (C) 1994-1998, 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 inverse-DCT routines that produce reduced-size output: |
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9 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block. |
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10 * |
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11 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M) |
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12 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step |
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13 * with an 8-to-4 step that produces the four averages of two adjacent outputs |
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14 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output). |
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15 * These steps were derived by computing the corresponding values at the end |
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16 * of the normal LL&M code, then simplifying as much as possible. |
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17 * |
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18 * 1x1 is trivial: just take the DC coefficient divided by 8. |
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19 * |
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20 * See jidctint.c for additional comments. |
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21 */ |
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22 |
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23 #define JPEG_INTERNALS |
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24 #include "jinclude.h" |
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25 #include "jpeglib.h" |
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26 #include "jdct.h" /* Private declarations for DCT subsystem */ |
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27 |
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28 #ifdef IDCT_SCALING_SUPPORTED |
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29 |
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30 |
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31 /* |
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32 * This module is specialized to the case DCTSIZE = 8. |
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33 */ |
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34 |
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35 #if DCTSIZE != 8 |
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36 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ |
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37 #endif |
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38 |
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39 |
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40 /* Scaling is the same as in jidctint.c. */ |
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41 |
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42 #if BITS_IN_JSAMPLE == 8 |
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43 #define CONST_BITS 13 |
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44 #define PASS1_BITS 2 |
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45 #else |
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46 #define CONST_BITS 13 |
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47 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */ |
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48 #endif |
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49 |
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50 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus |
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51 * causing a lot of useless floating-point operations at run time. |
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52 * To get around this we use the following pre-calculated constants. |
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53 * If you change CONST_BITS you may want to add appropriate values. |
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54 * (With a reasonable C compiler, you can just rely on the FIX() macro...) |
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55 */ |
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56 |
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57 #if CONST_BITS == 13 |
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58 #define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */ |
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59 #define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */ |
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60 #define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */ |
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61 #define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */ |
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62 #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */ |
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63 #define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */ |
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64 #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */ |
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65 #define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */ |
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66 #define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */ |
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67 #define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */ |
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68 #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */ |
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69 #define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */ |
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70 #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */ |
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71 #define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */ |
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72 #else |
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73 #define FIX_0_211164243 FIX(0.211164243) |
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74 #define FIX_0_509795579 FIX(0.509795579) |
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75 #define FIX_0_601344887 FIX(0.601344887) |
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76 #define FIX_0_720959822 FIX(0.720959822) |
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77 #define FIX_0_765366865 FIX(0.765366865) |
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78 #define FIX_0_850430095 FIX(0.850430095) |
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79 #define FIX_0_899976223 FIX(0.899976223) |
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80 #define FIX_1_061594337 FIX(1.061594337) |
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81 #define FIX_1_272758580 FIX(1.272758580) |
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82 #define FIX_1_451774981 FIX(1.451774981) |
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83 #define FIX_1_847759065 FIX(1.847759065) |
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84 #define FIX_2_172734803 FIX(2.172734803) |
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85 #define FIX_2_562915447 FIX(2.562915447) |
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86 #define FIX_3_624509785 FIX(3.624509785) |
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87 #endif |
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88 |
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89 |
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90 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. |
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91 * For 8-bit samples with the recommended scaling, all the variable |
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92 * and constant values involved are no more than 16 bits wide, so a |
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93 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply. |
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94 * For 12-bit samples, a full 32-bit multiplication will be needed. |
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95 */ |
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96 |
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97 #if BITS_IN_JSAMPLE == 8 |
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98 #define MULTIPLY(var,const) MULTIPLY16C16(var,const) |
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99 #else |
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100 #define MULTIPLY(var,const) ((var) * (const)) |
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101 #endif |
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102 |
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103 |
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104 /* Dequantize a coefficient by multiplying it by the multiplier-table |
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105 * entry; produce an int result. In this module, both inputs and result |
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106 * are 16 bits or less, so either int or short multiply will work. |
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107 */ |
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108 |
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109 #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval)) |
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110 |
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111 |
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112 /* |
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113 * Perform dequantization and inverse DCT on one block of coefficients, |
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114 * producing a reduced-size 4x4 output block. |
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115 */ |
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116 |
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117 GLOBAL(void) |
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118 jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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119 JCOEFPTR coef_block, |
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120 JSAMPARRAY output_buf, JDIMENSION output_col) |
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121 { |
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122 INT32 tmp0, tmp2, tmp10, tmp12; |
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123 INT32 z1, z2, z3, z4; |
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124 JCOEFPTR inptr; |
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125 ISLOW_MULT_TYPE * quantptr; |
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126 int * wsptr; |
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127 JSAMPROW outptr; |
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128 JSAMPLE *range_limit = IDCT_range_limit(cinfo); |
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129 int ctr; |
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130 int workspace[DCTSIZE*4]; /* buffers data between passes */ |
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131 SHIFT_TEMPS |
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132 |
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133 /* Pass 1: process columns from input, store into work array. */ |
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134 |
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135 inptr = coef_block; |
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136 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; |
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137 wsptr = workspace; |
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138 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { |
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139 /* Don't bother to process column 4, because second pass won't use it */ |
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140 if (ctr == DCTSIZE-4) |
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141 continue; |
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142 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 && |
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143 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 && |
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144 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) { |
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145 /* AC terms all zero; we need not examine term 4 for 4x4 output */ |
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146 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS; |
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147 |
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148 wsptr[DCTSIZE*0] = dcval; |
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149 wsptr[DCTSIZE*1] = dcval; |
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150 wsptr[DCTSIZE*2] = dcval; |
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151 wsptr[DCTSIZE*3] = dcval; |
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152 |
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153 continue; |
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154 } |
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155 |
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156 /* Even part */ |
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157 |
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158 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); |
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159 tmp0 <<= (CONST_BITS+1); |
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160 |
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161 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]); |
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162 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]); |
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163 |
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164 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865); |
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165 |
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166 tmp10 = tmp0 + tmp2; |
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167 tmp12 = tmp0 - tmp2; |
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168 |
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169 /* Odd part */ |
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170 |
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171 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); |
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172 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); |
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173 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); |
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174 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); |
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175 |
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176 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ |
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177 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ |
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178 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ |
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179 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ |
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180 |
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181 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ |
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182 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ |
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183 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ |
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184 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ |
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185 |
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186 /* Final output stage */ |
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187 |
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188 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1); |
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189 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1); |
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190 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1); |
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191 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1); |
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192 } |
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193 |
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194 /* Pass 2: process 4 rows from work array, store into output array. */ |
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195 |
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196 wsptr = workspace; |
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197 for (ctr = 0; ctr < 4; ctr++) { |
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198 outptr = output_buf[ctr] + output_col; |
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199 /* It's not clear whether a zero row test is worthwhile here ... */ |
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200 |
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201 #ifndef NO_ZERO_ROW_TEST |
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202 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && |
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203 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) { |
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204 /* AC terms all zero */ |
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205 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) |
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206 & RANGE_MASK]; |
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207 |
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208 outptr[0] = dcval; |
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209 outptr[1] = dcval; |
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210 outptr[2] = dcval; |
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211 outptr[3] = dcval; |
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212 |
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213 wsptr += DCTSIZE; /* advance pointer to next row */ |
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214 continue; |
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215 } |
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216 #endif |
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217 |
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218 /* Even part */ |
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219 |
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220 tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1); |
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221 |
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222 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065) |
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223 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865); |
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224 |
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225 tmp10 = tmp0 + tmp2; |
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226 tmp12 = tmp0 - tmp2; |
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227 |
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228 /* Odd part */ |
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229 |
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230 z1 = (INT32) wsptr[7]; |
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231 z2 = (INT32) wsptr[5]; |
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232 z3 = (INT32) wsptr[3]; |
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233 z4 = (INT32) wsptr[1]; |
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234 |
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235 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */ |
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236 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */ |
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237 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */ |
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238 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */ |
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239 |
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240 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */ |
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241 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */ |
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242 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */ |
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243 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */ |
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244 |
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245 /* Final output stage */ |
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246 |
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247 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2, |
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248 CONST_BITS+PASS1_BITS+3+1) |
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249 & RANGE_MASK]; |
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250 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2, |
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251 CONST_BITS+PASS1_BITS+3+1) |
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252 & RANGE_MASK]; |
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253 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0, |
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254 CONST_BITS+PASS1_BITS+3+1) |
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255 & RANGE_MASK]; |
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256 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0, |
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257 CONST_BITS+PASS1_BITS+3+1) |
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258 & RANGE_MASK]; |
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259 |
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260 wsptr += DCTSIZE; /* advance pointer to next row */ |
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261 } |
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262 } |
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263 |
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264 |
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265 /* |
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266 * Perform dequantization and inverse DCT on one block of coefficients, |
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267 * producing a reduced-size 2x2 output block. |
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268 */ |
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269 |
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270 GLOBAL(void) |
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271 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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272 JCOEFPTR coef_block, |
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273 JSAMPARRAY output_buf, JDIMENSION output_col) |
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274 { |
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275 INT32 tmp0, tmp10, z1; |
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276 JCOEFPTR inptr; |
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277 ISLOW_MULT_TYPE * quantptr; |
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278 int * wsptr; |
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279 JSAMPROW outptr; |
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280 JSAMPLE *range_limit = IDCT_range_limit(cinfo); |
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281 int ctr; |
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282 int workspace[DCTSIZE*2]; /* buffers data between passes */ |
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283 SHIFT_TEMPS |
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284 |
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285 /* Pass 1: process columns from input, store into work array. */ |
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286 |
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287 inptr = coef_block; |
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288 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; |
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289 wsptr = workspace; |
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290 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) { |
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291 /* Don't bother to process columns 2,4,6 */ |
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292 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6) |
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293 continue; |
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294 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 && |
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295 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) { |
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296 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */ |
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297 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS; |
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298 |
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299 wsptr[DCTSIZE*0] = dcval; |
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300 wsptr[DCTSIZE*1] = dcval; |
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301 |
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302 continue; |
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303 } |
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304 |
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305 /* Even part */ |
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306 |
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307 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]); |
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308 tmp10 = z1 << (CONST_BITS+2); |
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309 |
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310 /* Odd part */ |
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311 |
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312 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]); |
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313 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */ |
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314 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]); |
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315 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */ |
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316 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]); |
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317 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */ |
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318 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]); |
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319 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ |
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320 |
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321 /* Final output stage */ |
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322 |
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323 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2); |
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324 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2); |
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325 } |
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326 |
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327 /* Pass 2: process 2 rows from work array, store into output array. */ |
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328 |
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329 wsptr = workspace; |
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330 for (ctr = 0; ctr < 2; ctr++) { |
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331 outptr = output_buf[ctr] + output_col; |
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332 /* It's not clear whether a zero row test is worthwhile here ... */ |
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333 |
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334 #ifndef NO_ZERO_ROW_TEST |
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335 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) { |
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336 /* AC terms all zero */ |
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337 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3) |
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338 & RANGE_MASK]; |
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339 |
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340 outptr[0] = dcval; |
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341 outptr[1] = dcval; |
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342 |
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343 wsptr += DCTSIZE; /* advance pointer to next row */ |
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344 continue; |
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345 } |
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346 #endif |
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347 |
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348 /* Even part */ |
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349 |
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350 tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2); |
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351 |
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352 /* Odd part */ |
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353 |
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354 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */ |
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355 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */ |
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356 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */ |
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357 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */ |
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358 |
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359 /* Final output stage */ |
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360 |
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361 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0, |
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362 CONST_BITS+PASS1_BITS+3+2) |
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363 & RANGE_MASK]; |
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364 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0, |
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365 CONST_BITS+PASS1_BITS+3+2) |
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366 & RANGE_MASK]; |
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367 |
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368 wsptr += DCTSIZE; /* advance pointer to next row */ |
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369 } |
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370 } |
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371 |
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372 |
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373 /* |
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374 * Perform dequantization and inverse DCT on one block of coefficients, |
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375 * producing a reduced-size 1x1 output block. |
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376 */ |
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377 |
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378 GLOBAL(void) |
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379 jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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380 JCOEFPTR coef_block, |
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381 JSAMPARRAY output_buf, JDIMENSION output_col) |
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382 { |
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383 int dcval; |
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384 ISLOW_MULT_TYPE * quantptr; |
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385 JSAMPLE *range_limit = IDCT_range_limit(cinfo); |
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386 SHIFT_TEMPS |
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387 |
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388 /* We hardly need an inverse DCT routine for this: just take the |
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389 * average pixel value, which is one-eighth of the DC coefficient. |
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390 */ |
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391 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table; |
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392 dcval = DEQUANTIZE(coef_block[0], quantptr[0]); |
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393 dcval = (int) DESCALE((INT32) dcval, 3); |
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394 |
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395 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK]; |
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396 } |
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397 |
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398 #endif /* IDCT_SCALING_SUPPORTED */ |