1 | /* |
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2 | * Copyright (c) 1990 The Regents of the University of California. |
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3 | * All rights reserved. |
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4 | * |
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5 | * Redistribution and use in source and binary forms are permitted |
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6 | * provided that the above copyright notice and this paragraph are |
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7 | * duplicated in all such forms and that any documentation, |
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8 | * advertising materials, and other materials related to such |
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9 | * distribution and use acknowledge that the software was developed |
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10 | * by the University of California, Berkeley. The name of the |
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11 | * University may not be used to endorse or promote products derived |
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12 | * from this software without specific prior written permission. |
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13 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR |
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14 | * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
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15 | * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
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16 | */ |
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17 | |
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18 | /* |
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19 | FUNCTION |
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20 | <<fseek>>, <<fseeko>>---set file position |
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21 | |
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22 | INDEX |
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23 | fseek |
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24 | INDEX |
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25 | fseeko |
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26 | INDEX |
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27 | _fseek_r |
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28 | INDEX |
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29 | _fseeko_r |
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30 | |
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31 | SYNOPSIS |
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32 | #include <stdio.h> |
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33 | int fseek(FILE *<[fp]>, long <[offset]>, int <[whence]>) |
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34 | int fseeko(FILE *<[fp]>, off_t <[offset]>, int <[whence]>) |
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35 | int _fseek_r(struct _reent *<[ptr]>, FILE *<[fp]>, |
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36 | long <[offset]>, int <[whence]>) |
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37 | int _fseeko_r(struct _reent *<[ptr]>, FILE *<[fp]>, |
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38 | off_t <[offset]>, int <[whence]>) |
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39 | |
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40 | DESCRIPTION |
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41 | Objects of type <<FILE>> can have a ``position'' that records how much |
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42 | of the file your program has already read. Many of the <<stdio>> functions |
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43 | depend on this position, and many change it as a side effect. |
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44 | |
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45 | You can use <<fseek>>/<<fseeko>> to set the position for the file identified by |
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46 | <[fp]>. The value of <[offset]> determines the new position, in one |
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47 | of three ways selected by the value of <[whence]> (defined as macros |
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48 | in `<<stdio.h>>'): |
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49 | |
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50 | <<SEEK_SET>>---<[offset]> is the absolute file position (an offset |
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51 | from the beginning of the file) desired. <[offset]> must be positive. |
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52 | |
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53 | <<SEEK_CUR>>---<[offset]> is relative to the current file position. |
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54 | <[offset]> can meaningfully be either positive or negative. |
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55 | |
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56 | <<SEEK_END>>---<[offset]> is relative to the current end of file. |
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57 | <[offset]> can meaningfully be either positive (to increase the size |
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58 | of the file) or negative. |
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59 | |
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60 | See <<ftell>>/<<ftello>> to determine the current file position. |
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61 | |
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62 | RETURNS |
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63 | <<fseek>>/<<fseeko>> return <<0>> when successful. On failure, the |
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64 | result is <<EOF>>. The reason for failure is indicated in <<errno>>: |
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65 | either <<ESPIPE>> (the stream identified by <[fp]> doesn't support |
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66 | repositioning) or <<EINVAL>> (invalid file position). |
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67 | |
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68 | PORTABILITY |
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69 | ANSI C requires <<fseek>>. |
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70 | |
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71 | <<fseeko>> is defined by the Single Unix specification. |
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72 | |
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73 | Supporting OS subroutines required: <<close>>, <<fstat>>, <<isatty>>, |
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74 | <<lseek>>, <<read>>, <<sbrk>>, <<write>>. |
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75 | */ |
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76 | |
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77 | #include <_ansi.h> |
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78 | #include <reent.h> |
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79 | #include <stdio.h> |
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80 | #include <string.h> |
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81 | #include <time.h> |
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82 | #include <fcntl.h> |
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83 | #include <stdlib.h> |
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84 | #include <errno.h> |
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85 | #include <sys/stat.h> |
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86 | #include "local.h" |
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87 | |
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88 | #define POS_ERR (-(_fpos_t)1) |
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89 | |
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90 | /* |
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91 | * Seek the given file to the given offset. |
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92 | * `Whence' must be one of the three SEEK_* macros. |
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93 | */ |
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94 | |
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95 | int |
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96 | _fseeko_r (struct _reent *ptr, |
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97 | register FILE *fp, |
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98 | _off_t offset, |
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99 | int whence) |
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100 | { |
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101 | _fpos_t (*seekfn) (struct _reent *, void *, _fpos_t, int); |
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102 | _fpos_t target; |
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103 | _fpos_t curoff = 0; |
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104 | size_t n; |
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105 | #ifdef __USE_INTERNAL_STAT64 |
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106 | struct stat64 st; |
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107 | #else |
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108 | struct stat st; |
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109 | #endif |
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110 | int havepos; |
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111 | |
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112 | /* Make sure stdio is set up. */ |
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113 | |
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114 | CHECK_INIT (ptr, fp); |
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115 | |
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116 | _newlib_flockfile_start (fp); |
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117 | |
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118 | /* If we've been doing some writing, and we're in append mode |
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119 | then we don't really know where the filepos is. */ |
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120 | |
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121 | if (fp->_flags & __SAPP && fp->_flags & __SWR) |
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122 | { |
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123 | /* So flush the buffer and seek to the end. */ |
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124 | _fflush_r (ptr, fp); |
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125 | } |
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126 | |
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127 | /* Have to be able to seek. */ |
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128 | |
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129 | if ((seekfn = fp->_seek) == NULL) |
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130 | { |
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131 | ptr->_errno = ESPIPE; /* ??? */ |
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132 | _newlib_flockfile_exit (fp); |
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133 | return EOF; |
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134 | } |
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135 | |
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136 | /* |
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137 | * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. |
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138 | * After this, whence is either SEEK_SET or SEEK_END. |
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139 | */ |
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140 | |
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141 | switch (whence) |
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142 | { |
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143 | case SEEK_CUR: |
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144 | /* |
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145 | * In order to seek relative to the current stream offset, |
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146 | * we have to first find the current stream offset a la |
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147 | * ftell (see ftell for details). |
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148 | */ |
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149 | _fflush_r (ptr, fp); /* may adjust seek offset on append stream */ |
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150 | if (fp->_flags & __SOFF) |
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151 | curoff = fp->_offset; |
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152 | else |
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153 | { |
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154 | curoff = seekfn (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR); |
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155 | if (curoff == -1L) |
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156 | { |
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157 | _newlib_flockfile_exit (fp); |
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158 | return EOF; |
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159 | } |
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160 | } |
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161 | if (fp->_flags & __SRD) |
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162 | { |
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163 | curoff -= fp->_r; |
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164 | if (HASUB (fp)) |
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165 | curoff -= fp->_ur; |
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166 | } |
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167 | else if (fp->_flags & __SWR && fp->_p != NULL) |
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168 | curoff += fp->_p - fp->_bf._base; |
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169 | |
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170 | offset += curoff; |
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171 | whence = SEEK_SET; |
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172 | havepos = 1; |
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173 | break; |
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174 | |
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175 | case SEEK_SET: |
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176 | case SEEK_END: |
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177 | havepos = 0; |
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178 | break; |
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179 | |
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180 | default: |
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181 | ptr->_errno = EINVAL; |
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182 | _newlib_flockfile_exit (fp); |
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183 | return (EOF); |
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184 | } |
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185 | |
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186 | /* |
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187 | * Can only optimise if: |
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188 | * reading (and not reading-and-writing); |
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189 | * not unbuffered; and |
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190 | * this is a `regular' Unix file (and hence seekfn==__sseek). |
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191 | * We must check __NBF first, because it is possible to have __NBF |
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192 | * and __SOPT both set. |
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193 | */ |
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194 | |
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195 | if (fp->_bf._base == NULL) |
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196 | __smakebuf_r (ptr, fp); |
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197 | |
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198 | #ifdef _FSEEK_OPTIMIZATION |
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199 | if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) |
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200 | goto dumb; |
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201 | if ((fp->_flags & __SOPT) == 0) |
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202 | { |
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203 | if (seekfn != __sseek |
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204 | || fp->_file < 0 |
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205 | #ifdef __USE_INTERNAL_STAT64 |
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206 | || _fstat64_r (ptr, fp->_file, &st) |
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207 | #else |
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208 | || _fstat_r (ptr, fp->_file, &st) |
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209 | #endif |
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210 | || (st.st_mode & S_IFMT) != S_IFREG) |
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211 | { |
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212 | fp->_flags |= __SNPT; |
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213 | goto dumb; |
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214 | } |
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215 | #ifdef HAVE_BLKSIZE |
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216 | fp->_blksize = st.st_blksize; |
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217 | #else |
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218 | fp->_blksize = 1024; |
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219 | #endif |
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220 | fp->_flags |= __SOPT; |
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221 | } |
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222 | |
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223 | /* |
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224 | * We are reading; we can try to optimise. |
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225 | * Figure out where we are going and where we are now. |
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226 | */ |
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227 | |
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228 | if (whence == SEEK_SET) |
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229 | target = offset; |
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230 | else |
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231 | { |
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232 | #ifdef __USE_INTERNAL_STAT64 |
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233 | if (_fstat64_r (ptr, fp->_file, &st)) |
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234 | #else |
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235 | if (_fstat_r (ptr, fp->_file, &st)) |
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236 | #endif |
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237 | goto dumb; |
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238 | target = st.st_size + offset; |
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239 | } |
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240 | |
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241 | if (!havepos) |
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242 | { |
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243 | if (fp->_flags & __SOFF) |
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244 | curoff = fp->_offset; |
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245 | else |
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246 | { |
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247 | curoff = seekfn (ptr, fp->_cookie, 0L, SEEK_CUR); |
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248 | if (curoff == POS_ERR) |
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249 | goto dumb; |
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250 | } |
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251 | curoff -= fp->_r; |
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252 | if (HASUB (fp)) |
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253 | curoff -= fp->_ur; |
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254 | } |
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255 | |
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256 | /* |
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257 | * Compute the number of bytes in the input buffer (pretending |
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258 | * that any ungetc() input has been discarded). Adjust current |
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259 | * offset backwards by this count so that it represents the |
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260 | * file offset for the first byte in the current input buffer. |
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261 | */ |
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262 | |
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263 | if (HASUB (fp)) |
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264 | { |
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265 | curoff += fp->_r; /* kill off ungetc */ |
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266 | n = fp->_up - fp->_bf._base; |
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267 | curoff -= n; |
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268 | n += fp->_ur; |
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269 | } |
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270 | else |
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271 | { |
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272 | n = fp->_p - fp->_bf._base; |
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273 | curoff -= n; |
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274 | n += fp->_r; |
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275 | } |
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276 | |
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277 | /* |
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278 | * If the target offset is within the current buffer, |
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279 | * simply adjust the pointers, clear EOF, undo ungetc(), |
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280 | * and return. |
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281 | */ |
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282 | |
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283 | if (target >= curoff && target < curoff + n) |
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284 | { |
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285 | register int o = target - curoff; |
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286 | |
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287 | fp->_p = fp->_bf._base + o; |
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288 | fp->_r = n - o; |
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289 | if (HASUB (fp)) |
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290 | FREEUB (ptr, fp); |
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291 | fp->_flags &= ~__SEOF; |
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292 | memset (&fp->_mbstate, 0, sizeof (_mbstate_t)); |
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293 | _newlib_flockfile_exit (fp); |
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294 | return 0; |
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295 | } |
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296 | |
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297 | /* |
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298 | * The place we want to get to is not within the current buffer, |
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299 | * but we can still be kind to the kernel copyout mechanism. |
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300 | * By aligning the file offset to a block boundary, we can let |
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301 | * the kernel use the VM hardware to map pages instead of |
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302 | * copying bytes laboriously. Using a block boundary also |
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303 | * ensures that we only read one block, rather than two. |
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304 | */ |
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305 | |
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306 | curoff = target & ~(fp->_blksize - 1); |
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307 | if (seekfn (ptr, fp->_cookie, curoff, SEEK_SET) == POS_ERR) |
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308 | goto dumb; |
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309 | fp->_r = 0; |
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310 | fp->_p = fp->_bf._base; |
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311 | if (HASUB (fp)) |
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312 | FREEUB (ptr, fp); |
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313 | fp->_flags &= ~__SEOF; |
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314 | n = target - curoff; |
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315 | if (n) |
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316 | { |
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317 | if (__srefill_r (ptr, fp) || fp->_r < n) |
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318 | goto dumb; |
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319 | fp->_p += n; |
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320 | fp->_r -= n; |
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321 | } |
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322 | memset (&fp->_mbstate, 0, sizeof (_mbstate_t)); |
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323 | _newlib_flockfile_exit (fp); |
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324 | return 0; |
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325 | |
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326 | /* |
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327 | * We get here if we cannot optimise the seek ... just |
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328 | * do it. Allow the seek function to change fp->_bf._base. |
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329 | */ |
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330 | #endif |
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331 | |
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332 | dumb: |
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333 | if (_fflush_r (ptr, fp) |
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334 | || seekfn (ptr, fp->_cookie, offset, whence) == POS_ERR) |
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335 | { |
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336 | _newlib_flockfile_exit (fp); |
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337 | return EOF; |
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338 | } |
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339 | /* success: clear EOF indicator and discard ungetc() data */ |
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340 | if (HASUB (fp)) |
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341 | FREEUB (ptr, fp); |
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342 | fp->_p = fp->_bf._base; |
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343 | fp->_r = 0; |
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344 | /* fp->_w = 0; *//* unnecessary (I think...) */ |
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345 | fp->_flags &= ~__SEOF; |
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346 | /* Reset no-optimization flag after successful seek. The |
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347 | no-optimization flag may be set in the case of a read |
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348 | stream that is flushed which by POSIX/SUSv3 standards, |
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349 | means that a corresponding seek must not optimize. The |
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350 | optimization is then allowed if no subsequent flush |
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351 | is performed. */ |
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352 | fp->_flags &= ~__SNPT; |
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353 | memset (&fp->_mbstate, 0, sizeof (_mbstate_t)); |
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354 | _newlib_flockfile_end (fp); |
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355 | return 0; |
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356 | } |
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357 | |
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358 | #ifndef _REENT_ONLY |
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359 | |
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360 | int |
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361 | fseeko (register FILE *fp, |
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362 | _off_t offset, |
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363 | int whence) |
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364 | { |
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365 | return _fseeko_r (_REENT, fp, offset, whence); |
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366 | } |
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367 | |
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368 | #endif /* !_REENT_ONLY */ |
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