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1 /* |
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2 * jdct.h |
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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 include file contains common declarations for the forward and |
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9 * inverse DCT modules. These declarations are private to the DCT managers |
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10 * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms. |
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11 * The individual DCT algorithms are kept in separate files to ease |
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12 * machine-dependent tuning (e.g., assembly coding). |
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13 */ |
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14 |
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15 |
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16 /* |
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17 * A forward DCT routine is given a pointer to a work area of type DCTELEM[]; |
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18 * the DCT is to be performed in-place in that buffer. Type DCTELEM is int |
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19 * for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT |
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20 * implementations use an array of type FAST_FLOAT, instead.) |
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21 * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE). |
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22 * The DCT outputs are returned scaled up by a factor of 8; they therefore |
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23 * have a range of +-8K for 8-bit data, +-128K for 12-bit data. This |
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24 * convention improves accuracy in integer implementations and saves some |
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25 * work in floating-point ones. |
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26 * Quantization of the output coefficients is done by jcdctmgr.c. |
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27 */ |
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28 |
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29 #if BITS_IN_JSAMPLE == 8 |
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30 typedef int DCTELEM; /* 16 or 32 bits is fine */ |
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31 #else |
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32 typedef INT32 DCTELEM; /* must have 32 bits */ |
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33 #endif |
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34 |
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35 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data)); |
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36 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data)); |
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37 |
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38 |
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39 /* |
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40 * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer |
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41 * to an output sample array. The routine must dequantize the input data as |
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42 * well as perform the IDCT; for dequantization, it uses the multiplier table |
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43 * pointed to by compptr->dct_table. The output data is to be placed into the |
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44 * sample array starting at a specified column. (Any row offset needed will |
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45 * be applied to the array pointer before it is passed to the IDCT code.) |
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46 * Note that the number of samples emitted by the IDCT routine is |
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47 * DCT_scaled_size * DCT_scaled_size. |
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48 */ |
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49 |
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50 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */ |
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51 |
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52 /* |
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53 * Each IDCT routine has its own ideas about the best dct_table element type. |
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54 */ |
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55 |
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56 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */ |
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57 #if BITS_IN_JSAMPLE == 8 |
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58 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */ |
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59 #define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */ |
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60 #else |
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61 typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */ |
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62 #define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */ |
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63 #endif |
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64 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */ |
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65 |
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66 |
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67 /* |
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68 * Each IDCT routine is responsible for range-limiting its results and |
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69 * converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could |
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70 * be quite far out of range if the input data is corrupt, so a bulletproof |
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71 * range-limiting step is required. We use a mask-and-table-lookup method |
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72 * to do the combined operations quickly. See the comments with |
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73 * prepare_range_limit_table (in jdmaster.c) for more info. |
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74 */ |
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75 |
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76 #define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE) |
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77 |
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78 #define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */ |
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79 |
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80 |
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81 /* Short forms of external names for systems with brain-damaged linkers. */ |
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82 |
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83 #ifdef NEED_SHORT_EXTERNAL_NAMES |
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84 #define jpeg_fdct_islow jFDislow |
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85 #define jpeg_fdct_ifast jFDifast |
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86 #define jpeg_fdct_float jFDfloat |
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87 #define jpeg_idct_islow jRDislow |
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88 #define jpeg_idct_ifast jRDifast |
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89 #define jpeg_idct_float jRDfloat |
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90 #define jpeg_idct_4x4 jRD4x4 |
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91 #define jpeg_idct_2x2 jRD2x2 |
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92 #define jpeg_idct_1x1 jRD1x1 |
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93 #endif /* NEED_SHORT_EXTERNAL_NAMES */ |
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94 |
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95 /* Extern declarations for the forward and inverse DCT routines. */ |
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96 |
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97 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data)); |
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98 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data)); |
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99 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data)); |
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100 |
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101 EXTERN(void) jpeg_idct_islow |
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102 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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103 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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104 EXTERN(void) jpeg_idct_ifast |
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105 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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106 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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107 EXTERN(void) jpeg_idct_float |
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108 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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109 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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110 EXTERN(void) jpeg_idct_4x4 |
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111 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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112 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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113 EXTERN(void) jpeg_idct_2x2 |
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114 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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115 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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116 EXTERN(void) jpeg_idct_1x1 |
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117 JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr, |
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118 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col)); |
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119 |
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120 |
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121 /* |
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122 * Macros for handling fixed-point arithmetic; these are used by many |
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123 * but not all of the DCT/IDCT modules. |
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124 * |
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125 * All values are expected to be of type INT32. |
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126 * Fractional constants are scaled left by CONST_BITS bits. |
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127 * CONST_BITS is defined within each module using these macros, |
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128 * and may differ from one module to the next. |
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129 */ |
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130 |
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131 #define ONE ((INT32) 1) |
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132 #define CONST_SCALE (ONE << CONST_BITS) |
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133 |
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134 /* Convert a positive real constant to an integer scaled by CONST_SCALE. |
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135 * Caution: some C compilers fail to reduce "FIX(constant)" at compile time, |
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136 * thus causing a lot of useless floating-point operations at run time. |
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137 */ |
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138 |
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139 #define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5)) |
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140 |
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141 /* Descale and correctly round an INT32 value that's scaled by N bits. |
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142 * We assume RIGHT_SHIFT rounds towards minus infinity, so adding |
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143 * the fudge factor is correct for either sign of X. |
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144 */ |
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145 |
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146 #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n) |
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147 |
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148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result. |
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149 * This macro is used only when the two inputs will actually be no more than |
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150 * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a |
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151 * full 32x32 multiply. This provides a useful speedup on many machines. |
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152 * Unfortunately there is no way to specify a 16x16->32 multiply portably |
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153 * in C, but some C compilers will do the right thing if you provide the |
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154 * correct combination of casts. |
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155 */ |
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156 |
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157 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ |
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158 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const))) |
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159 #endif |
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160 #ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */ |
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161 #define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const))) |
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162 #endif |
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163 |
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164 #ifndef MULTIPLY16C16 /* default definition */ |
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165 #define MULTIPLY16C16(var,const) ((var) * (const)) |
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166 #endif |
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167 |
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168 /* Same except both inputs are variables. */ |
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169 |
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170 #ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */ |
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171 #define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2))) |
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172 #endif |
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173 |
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174 #ifndef MULTIPLY16V16 /* default definition */ |
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175 #define MULTIPLY16V16(var1,var2) ((var1) * (var2)) |
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176 #endif |