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Rev | Author | Line No. | Line |
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1085 | pj | 1 | /* idct.c, inverse fast discrete cosine transform */ |
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3 | /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */ |
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4 | |||
5 | /* |
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6 | * Disclaimer of Warranty |
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7 | * |
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8 | * These software programs are available to the user without any license fee or |
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9 | * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims |
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10 | * any and all warranties, whether express, implied, or statuary, including any |
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11 | * implied warranties or merchantability or of fitness for a particular |
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12 | * purpose. In no event shall the copyright-holder be liable for any |
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13 | * incidental, punitive, or consequential damages of any kind whatsoever |
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14 | * arising from the use of these programs. |
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15 | * |
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16 | * This disclaimer of warranty extends to the user of these programs and user's |
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17 | * customers, employees, agents, transferees, successors, and assigns. |
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18 | * |
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19 | * The MPEG Software Simulation Group does not represent or warrant that the |
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20 | * programs furnished hereunder are free of infringement of any third-party |
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21 | * patents. |
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22 | * |
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23 | * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware, |
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24 | * are subject to royalty fees to patent holders. Many of these patents are |
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25 | * general enough such that they are unavoidable regardless of implementation |
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26 | * design. |
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27 | * |
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28 | */ |
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29 | |||
30 | /**********************************************************/ |
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31 | /* inverse two dimensional DCT, Chen-Wang algorithm */ |
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32 | /* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984) */ |
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33 | /* 32-bit integer arithmetic (8 bit coefficients) */ |
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34 | /* 11 mults, 29 adds per DCT */ |
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35 | /* sE, 18.8.91 */ |
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36 | /**********************************************************/ |
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37 | /* coefficients extended to 12 bit for IEEE1180-1990 */ |
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38 | /* compliance sE, 2.1.94 */ |
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39 | /**********************************************************/ |
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40 | |||
41 | /* this code assumes >> to be a two's-complement arithmetic */ |
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42 | /* right shift: (-2)>>1 == -1 , (-3)>>1 == -2 */ |
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43 | |||
44 | #include "config.h" |
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45 | |||
46 | #define W1 2841 /* 2048*sqrt(2)*cos(1*pi/16) */ |
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47 | #define W2 2676 /* 2048*sqrt(2)*cos(2*pi/16) */ |
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48 | #define W3 2408 /* 2048*sqrt(2)*cos(3*pi/16) */ |
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49 | #define W5 1609 /* 2048*sqrt(2)*cos(5*pi/16) */ |
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50 | #define W6 1108 /* 2048*sqrt(2)*cos(6*pi/16) */ |
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51 | #define W7 565 /* 2048*sqrt(2)*cos(7*pi/16) */ |
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52 | |||
53 | /* global declarations */ |
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54 | void Initialize_Fast_IDCT _ANSI_ARGS_((void)); |
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55 | void Fast_IDCT _ANSI_ARGS_((short *block)); |
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56 | |||
57 | /* private data */ |
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58 | static short iclip[1024]; /* clipping table */ |
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59 | static short *iclp; |
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60 | |||
61 | /* private prototypes */ |
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62 | static void idctrow _ANSI_ARGS_((short *blk)); |
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63 | static void idctcol _ANSI_ARGS_((short *blk)); |
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64 | |||
65 | /* row (horizontal) IDCT |
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66 | * |
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67 | * 7 pi 1 |
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68 | * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l ) |
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69 | * l=0 8 2 |
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70 | * |
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71 | * where: c[0] = 128 |
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72 | * c[1..7] = 128*sqrt(2) |
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73 | */ |
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74 | |||
75 | static void idctrow(blk) |
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76 | short *blk; |
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77 | { |
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78 | int x0, x1, x2, x3, x4, x5, x6, x7, x8; |
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79 | |||
80 | /* shortcut */ |
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81 | if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) | |
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82 | (x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3]))) |
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83 | { |
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84 | blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3; |
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85 | return; |
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86 | } |
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87 | |||
88 | x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */ |
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89 | |||
90 | /* first stage */ |
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91 | x8 = W7*(x4+x5); |
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92 | x4 = x8 + (W1-W7)*x4; |
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93 | x5 = x8 - (W1+W7)*x5; |
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94 | x8 = W3*(x6+x7); |
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95 | x6 = x8 - (W3-W5)*x6; |
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96 | x7 = x8 - (W3+W5)*x7; |
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97 | |||
98 | /* second stage */ |
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99 | x8 = x0 + x1; |
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100 | x0 -= x1; |
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101 | x1 = W6*(x3+x2); |
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102 | x2 = x1 - (W2+W6)*x2; |
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103 | x3 = x1 + (W2-W6)*x3; |
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104 | x1 = x4 + x6; |
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105 | x4 -= x6; |
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106 | x6 = x5 + x7; |
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107 | x5 -= x7; |
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108 | |||
109 | /* third stage */ |
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110 | x7 = x8 + x3; |
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111 | x8 -= x3; |
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112 | x3 = x0 + x2; |
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113 | x0 -= x2; |
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114 | x2 = (181*(x4+x5)+128)>>8; |
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115 | x4 = (181*(x4-x5)+128)>>8; |
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116 | |||
117 | /* fourth stage */ |
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118 | blk[0] = (x7+x1)>>8; |
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119 | blk[1] = (x3+x2)>>8; |
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120 | blk[2] = (x0+x4)>>8; |
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121 | blk[3] = (x8+x6)>>8; |
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122 | blk[4] = (x8-x6)>>8; |
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123 | blk[5] = (x0-x4)>>8; |
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124 | blk[6] = (x3-x2)>>8; |
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125 | blk[7] = (x7-x1)>>8; |
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126 | } |
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127 | |||
128 | /* column (vertical) IDCT |
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129 | * |
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130 | * 7 pi 1 |
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131 | * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l ) |
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132 | * l=0 8 2 |
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133 | * |
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134 | * where: c[0] = 1/1024 |
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135 | * c[1..7] = (1/1024)*sqrt(2) |
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136 | */ |
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137 | static void idctcol(blk) |
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138 | short *blk; |
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139 | { |
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140 | int x0, x1, x2, x3, x4, x5, x6, x7, x8; |
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141 | |||
142 | /* shortcut */ |
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143 | if (!((x1 = (blk[8*4]<<8)) | (x2 = blk[8*6]) | (x3 = blk[8*2]) | |
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144 | (x4 = blk[8*1]) | (x5 = blk[8*7]) | (x6 = blk[8*5]) | (x7 = blk[8*3]))) |
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145 | { |
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146 | blk[8*0]=blk[8*1]=blk[8*2]=blk[8*3]=blk[8*4]=blk[8*5]=blk[8*6]=blk[8*7]= |
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147 | iclp[(blk[8*0]+32)>>6]; |
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148 | return; |
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149 | } |
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150 | |||
151 | x0 = (blk[8*0]<<8) + 8192; |
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152 | |||
153 | /* first stage */ |
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154 | x8 = W7*(x4+x5) + 4; |
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155 | x4 = (x8+(W1-W7)*x4)>>3; |
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156 | x5 = (x8-(W1+W7)*x5)>>3; |
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157 | x8 = W3*(x6+x7) + 4; |
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158 | x6 = (x8-(W3-W5)*x6)>>3; |
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159 | x7 = (x8-(W3+W5)*x7)>>3; |
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160 | |||
161 | /* second stage */ |
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162 | x8 = x0 + x1; |
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163 | x0 -= x1; |
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164 | x1 = W6*(x3+x2) + 4; |
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165 | x2 = (x1-(W2+W6)*x2)>>3; |
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166 | x3 = (x1+(W2-W6)*x3)>>3; |
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167 | x1 = x4 + x6; |
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168 | x4 -= x6; |
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169 | x6 = x5 + x7; |
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170 | x5 -= x7; |
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171 | |||
172 | /* third stage */ |
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173 | x7 = x8 + x3; |
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174 | x8 -= x3; |
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175 | x3 = x0 + x2; |
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176 | x0 -= x2; |
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177 | x2 = (181*(x4+x5)+128)>>8; |
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178 | x4 = (181*(x4-x5)+128)>>8; |
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179 | |||
180 | /* fourth stage */ |
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181 | blk[8*0] = iclp[(x7+x1)>>14]; |
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182 | blk[8*1] = iclp[(x3+x2)>>14]; |
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183 | blk[8*2] = iclp[(x0+x4)>>14]; |
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184 | blk[8*3] = iclp[(x8+x6)>>14]; |
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185 | blk[8*4] = iclp[(x8-x6)>>14]; |
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186 | blk[8*5] = iclp[(x0-x4)>>14]; |
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187 | blk[8*6] = iclp[(x3-x2)>>14]; |
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188 | blk[8*7] = iclp[(x7-x1)>>14]; |
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189 | } |
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190 | |||
191 | /* two dimensional inverse discrete cosine transform */ |
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192 | void Fast_IDCT(block) |
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193 | short *block; |
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194 | { |
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195 | int i; |
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196 | |||
197 | for (i=0; i<8; i++) |
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198 | idctrow(block+8*i); |
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199 | |||
200 | for (i=0; i<8; i++) |
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201 | idctcol(block+i); |
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202 | } |
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203 | |||
204 | void Initialize_Fast_IDCT() |
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205 | { |
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206 | int i; |
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207 | |||
208 | iclp = iclip+512; |
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209 | for (i= -512; i<512; i++) |
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210 | iclp[i] = (i<-256) ? -256 : ((i>255) ? 255 : i); |
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211 | } |