1 | |
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2 | /* @(#)s_lrint.c 5.1 93/09/24 */ |
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3 | /* |
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4 | * ==================================================== |
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5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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6 | * |
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7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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8 | * Permission to use, copy, modify, and distribute this |
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9 | * software is freely granted, provided that this notice |
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10 | * is preserved. |
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11 | * ==================================================== |
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12 | */ |
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13 | /* |
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14 | FUNCTION |
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15 | <<lrint>>, <<lrintf>>, <<llrint>>, <<llrintf>>---round to integer |
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16 | INDEX |
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17 | lrint |
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18 | INDEX |
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19 | lrintf |
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20 | INDEX |
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21 | llrint |
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22 | INDEX |
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23 | llrintf |
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24 | |
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25 | SYNOPSIS |
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26 | #include <math.h> |
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27 | long int lrint(double <[x]>); |
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28 | long int lrintf(float <[x]>); |
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29 | long long int llrint(double <[x]>); |
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30 | long long int llrintf(float <[x]>); |
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31 | |
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32 | DESCRIPTION |
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33 | The <<lrint>> and <<llrint>> functions round their argument to the nearest |
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34 | integer value, using the current rounding direction. If the rounded value is |
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35 | outside the range of the return type, the numeric result is unspecified. A |
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36 | range error may occur if the magnitude of <[x]> is too large. |
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37 | The "inexact" floating-point exception is raised in implementations that |
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38 | support it when the result differs in value from the argument (i.e., when |
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39 | a fraction actually has been truncated). |
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40 | |
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41 | RETURNS |
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42 | <[x]> rounded to an integral value, using the current rounding direction. |
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43 | |
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44 | SEEALSO |
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45 | <<lround>> |
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46 | |
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47 | PORTABILITY |
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48 | ANSI C, POSIX |
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49 | |
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50 | */ |
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51 | |
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52 | /* |
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53 | * lrint(x) |
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54 | * Return x rounded to integral value according to the prevailing |
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55 | * rounding mode. |
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56 | * Method: |
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57 | * Using floating addition. |
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58 | * Exception: |
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59 | * Inexact flag raised if x not equal to lrint(x). |
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60 | */ |
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61 | |
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62 | #include "fdlibm.h" |
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63 | |
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64 | #ifndef _DOUBLE_IS_32BITS |
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65 | |
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66 | #ifdef __STDC__ |
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67 | static const double |
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68 | #else |
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69 | static double |
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70 | #endif |
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71 | |
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72 | /* Adding a double, x, to 2^52 will cause the result to be rounded based on |
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73 | the fractional part of x, according to the implementation's current rounding |
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74 | mode. 2^52 is the smallest double that can be represented using all 52 significant |
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75 | digits. */ |
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76 | TWO52[2]={ |
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77 | 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ |
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78 | -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ |
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79 | }; |
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80 | |
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81 | #ifdef __STDC__ |
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82 | long int lrint(double x) |
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83 | #else |
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84 | long int lrint(x) |
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85 | double x; |
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86 | #endif |
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87 | { |
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88 | __int32_t i0,j0,sx; |
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89 | __uint32_t i1; |
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90 | double t; |
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91 | volatile double w; |
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92 | long int result; |
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93 | |
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94 | EXTRACT_WORDS(i0,i1,x); |
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95 | |
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96 | /* Extract sign bit. */ |
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97 | sx = (i0>>31)&1; |
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98 | |
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99 | /* Extract exponent field. */ |
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100 | j0 = ((i0 & 0x7ff00000) >> 20) - 1023; |
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101 | /* j0 in [-1023,1024] */ |
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102 | |
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103 | if(j0 < 20) |
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104 | { |
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105 | /* j0 in [-1023,19] */ |
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106 | if(j0 < -1) |
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107 | return 0; |
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108 | else |
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109 | { |
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110 | /* j0 in [0,19] */ |
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111 | /* shift amt in [0,19] */ |
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112 | w = TWO52[sx] + x; |
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113 | t = w - TWO52[sx]; |
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114 | GET_HIGH_WORD(i0, t); |
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115 | /* Detect the all-zeros representation of plus and |
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116 | minus zero, which fails the calculation below. */ |
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117 | if ((i0 & ~(1L << 31)) == 0) |
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118 | return 0; |
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119 | /* After round: j0 in [0,20] */ |
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120 | j0 = ((i0 & 0x7ff00000) >> 20) - 1023; |
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121 | i0 &= 0x000fffff; |
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122 | i0 |= 0x00100000; |
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123 | /* shift amt in [20,0] */ |
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124 | result = i0 >> (20 - j0); |
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125 | } |
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126 | } |
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127 | else if (j0 < (int)(8 * sizeof (long int)) - 1) |
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128 | { |
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129 | /* 32bit return: j0 in [20,30] */ |
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130 | /* 64bit return: j0 in [20,62] */ |
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131 | if (j0 >= 52) |
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132 | /* 64bit return: j0 in [52,62] */ |
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133 | /* 64bit return: left shift amt in [32,42] */ |
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134 | result = ((long int) ((i0 & 0x000fffff) | 0x0010000) << (j0 - 20)) | |
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135 | /* 64bit return: right shift amt in [0,10] */ |
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136 | (i1 << (j0 - 52)); |
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137 | else |
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138 | { |
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139 | /* 32bit return: j0 in [20,30] */ |
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140 | /* 64bit return: j0 in [20,51] */ |
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141 | w = TWO52[sx] + x; |
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142 | t = w - TWO52[sx]; |
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143 | EXTRACT_WORDS (i0, i1, t); |
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144 | j0 = ((i0 & 0x7ff00000) >> 20) - 1023; |
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145 | i0 &= 0x000fffff; |
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146 | i0 |= 0x00100000; |
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147 | /* After round: |
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148 | * 32bit return: j0 in [20,31]; |
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149 | * 64bit return: j0 in [20,52] */ |
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150 | /* 32bit return: left shift amt in [0,11] */ |
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151 | /* 64bit return: left shift amt in [0,32] */ |
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152 | /* ***32bit return: right shift amt in [32,21] */ |
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153 | /* ***64bit return: right shift amt in [32,0] */ |
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154 | result = ((long int) i0 << (j0 - 20)) |
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155 | | SAFE_RIGHT_SHIFT (i1, (52 - j0)); |
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156 | } |
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157 | } |
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158 | else |
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159 | { |
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160 | return (long int) x; |
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161 | } |
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162 | |
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163 | return sx ? -result : result; |
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164 | } |
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165 | |
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166 | #endif /* _DOUBLE_IS_32BITS */ |
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