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55 | pj | 1 | /* $Id: mmath.c,v 1.1 2003-02-28 11:42:03 pj Exp $ */ |
2 | |||
3 | /* |
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4 | * Mesa 3-D graphics library |
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5 | * Version: 3.5 |
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6 | * |
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7 | * Copyright (C) 1999-2001 Brian Paul All Rights Reserved. |
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8 | * |
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9 | * Permission is hereby granted, free of charge, to any person obtaining a |
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10 | * copy of this software and associated documentation files (the "Software"), |
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11 | * to deal in the Software without restriction, including without limitation |
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12 | * the rights to use, copy, modify, merge, publish, distribute, sublicense, |
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13 | * and/or sell copies of the Software, and to permit persons to whom the |
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14 | * Software is furnished to do so, subject to the following conditions: |
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15 | * |
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16 | * The above copyright notice and this permission notice shall be included |
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17 | * in all copies or substantial portions of the Software. |
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18 | * |
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19 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS |
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20 | * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
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21 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
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22 | * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN |
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23 | * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN |
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24 | * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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25 | */ |
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26 | |||
27 | |||
28 | #include "glheader.h" |
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29 | #include "mmath.h" |
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30 | |||
31 | |||
32 | static int in_fast_math; |
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33 | |||
34 | /* |
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35 | * A High Speed, Low Precision Square Root |
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36 | * by Paul Lalonde and Robert Dawson |
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37 | * from "Graphics Gems", Academic Press, 1990 |
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38 | */ |
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39 | |||
40 | /* |
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41 | * SPARC implementation of a fast square root by table |
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42 | * lookup. |
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43 | * SPARC floating point format is as follows: |
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44 | * |
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45 | * BIT 31 30 23 22 0 |
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46 | * sign exponent mantissa |
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47 | */ |
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48 | static short sqrttab[0x100]; /* declare table of square roots */ |
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49 | |||
50 | static void init_sqrt(void) |
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51 | { |
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52 | #ifdef FAST_MATH |
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53 | unsigned short i; |
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54 | fi_type fi; /* to access the bits of a float in C quickly */ |
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55 | /* we use a union defined in glheader.h */ |
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56 | |||
57 | for(i=0; i<= 0x7f; i++) { |
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58 | fi.i = 0; |
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59 | |||
60 | /* |
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61 | * Build a float with the bit pattern i as mantissa |
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62 | * and an exponent of 0, stored as 127 |
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63 | */ |
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64 | |||
65 | fi.i = (i << 16) | (127 << 23); |
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66 | fi.f = _mesa_sqrt(fi.f); |
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67 | |||
68 | /* |
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69 | * Take the square root then strip the first 7 bits of |
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70 | * the mantissa into the table |
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71 | */ |
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72 | |||
73 | sqrttab[i] = (fi.i & 0x7fffff) >> 16; |
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74 | |||
75 | /* |
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76 | * Repeat the process, this time with an exponent of |
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77 | * 1, stored as 128 |
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78 | */ |
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79 | |||
80 | fi.i = 0; |
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81 | fi.i = (i << 16) | (128 << 23); |
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82 | fi.f = sqrt(fi.f); |
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83 | sqrttab[i+0x80] = (fi.i & 0x7fffff) >> 16; |
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84 | } |
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85 | #else |
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86 | (void) sqrttab; /* silence compiler warnings */ |
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87 | #endif /*FAST_MATH*/ |
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88 | } |
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89 | |||
90 | |||
91 | float gl_sqrt( float x ) |
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92 | { |
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93 | #ifdef FAST_MATH |
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94 | fi_type num; |
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95 | /* to access the bits of a float in C |
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96 | * we use a union from glheader.h */ |
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97 | |||
98 | short e; /* the exponent */ |
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99 | if (x == 0.0F) return 0.0F; /* check for square root of 0 */ |
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100 | num.f = x; |
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101 | e = (num.i >> 23) - 127; /* get the exponent - on a SPARC the */ |
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102 | /* exponent is stored with 127 added */ |
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103 | num.i &= 0x7fffff; /* leave only the mantissa */ |
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104 | if (e & 0x01) num.i |= 0x800000; |
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105 | /* the exponent is odd so we have to */ |
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106 | /* look it up in the second half of */ |
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107 | /* the lookup table, so we set the */ |
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108 | /* high bit */ |
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109 | e >>= 1; /* divide the exponent by two */ |
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110 | /* note that in C the shift */ |
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111 | /* operators are sign preserving */ |
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112 | /* for signed operands */ |
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113 | /* Do the table lookup, based on the quaternary mantissa, |
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114 | * then reconstruct the result back into a float |
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115 | */ |
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116 | num.i = ((sqrttab[num.i >> 16]) << 16) | ((e + 127) << 23); |
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117 | return num.f; |
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118 | #else |
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119 | return (GLfloat) _mesa_sqrt(x); |
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120 | #endif |
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121 | } |
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122 | |||
123 | |||
124 | /* ubyte -> float conversion */ |
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125 | float _mesa_ubyte_to_float_color_tab[256]; |
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126 | |||
127 | |||
128 | /* |
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129 | * Initialize tables, etc for fast math functions. |
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130 | */ |
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131 | void |
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132 | _mesa_init_math(void) |
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133 | { |
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134 | static GLboolean initialized = GL_FALSE; |
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135 | |||
136 | if (!initialized) { |
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137 | int i; |
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138 | for (i = 0; i < 256; i++) { |
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139 | _mesa_ubyte_to_float_color_tab[i] = (float) i / 255.0F; |
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140 | } |
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141 | |||
142 | init_sqrt(); |
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143 | |||
144 | initialized = GL_TRUE; |
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145 | in_fast_math = 0; |
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146 | |||
147 | #if defined(_FPU_GETCW) && defined(_FPU_SETCW) |
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148 | { |
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149 | const char *debug = _mesa_getenv("MESA_DEBUG"); |
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150 | if (debug && _mesa_strcmp(debug, "FP")==0) { |
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151 | /* die on FP exceptions */ |
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152 | fpu_control_t mask; |
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153 | _FPU_GETCW(mask); |
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154 | mask &= ~(_FPU_MASK_IM | _FPU_MASK_DM | _FPU_MASK_ZM |
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155 | | _FPU_MASK_OM | _FPU_MASK_UM); |
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156 | _FPU_SETCW(mask); |
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157 | } |
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158 | } |
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159 | #endif |
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160 | } |
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161 | } |
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162 | |||
163 | |||
164 | |||
165 | /* |
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166 | * Return number of bits set in given GLuint. |
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167 | */ |
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168 | GLuint |
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169 | _mesa_bitcount(GLuint n) |
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170 | { |
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171 | GLuint bits; |
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172 | for (bits = 0; n > 0; n = n >> 1) { |
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173 | if (n & 1) { |
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174 | bits++; |
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175 | } |
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176 | } |
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177 | return bits; |
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178 | } |