Mercurial > hg > octave-nkf > gnulib-hg

annotate lib/freadseek.c @ 17605:23cb5b2fd95b

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relocatable-perl: like relocatable-script, but for Perl scripts * build-aux/relocatable.pl.in: Add. * doc/relocatable-maint.texi: Add documentation. * modules/relocatable-perl: Add.
author Reuben Thomas <rrt@sc3d.org>
date Thu, 09 Jan 2014 22:31:42 +0000
parents 344018b6e5d7
children ab58d4870664
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
9738
923434ebe936 New module 'freadseek'.
Bruno Haible <bruno@clisp.org>
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1 /* Skipping input from a FILE stream.
17587
344018b6e5d7 maint: update copyright
Eric Blake <eblake@redhat.com>
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2 Copyright (C) 2007-2014 Free Software Foundation, Inc.
9738
923434ebe936 New module 'freadseek'.
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3
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4 This program is free software: you can redistribute it and/or modify
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5 it under the terms of the GNU General Public License as published by
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6 the Free Software Foundation; either version 3 of the License, or
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7 (at your option) any later version.
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8
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9 This program is distributed in the hope that it will be useful,
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10 but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 GNU General Public License for more details.
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13
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14 You should have received a copy of the GNU General Public License
923434ebe936 New module 'freadseek'.
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15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
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16
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17 #include <config.h>
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18
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19 /* Specification. */
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20 #include "freadseek.h"
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21
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22 #include <stdlib.h>
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23 #include <unistd.h>
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24
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25 #include "freadahead.h"
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9ccce8a9bf52 Pass test-freadseek on cygwin.
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26 #include "freadptr.h"
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27
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28 #include "stdio-impl.h"
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29
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30 /* Increment the in-memory pointer. INCREMENT must be at most the buffer size
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31 returned by freadptr().
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32 This is very cheap (no system calls). */
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33 static void
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34 freadptrinc (FILE *fp, size_t increment)
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35 {
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36 /* Keep this code in sync with freadptr! */
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37 #if HAVE___FREADPTRINC /* musl libc */
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38 __freadptrinc (fp, increment);
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39 #elif defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
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40 fp->_IO_read_ptr += increment;
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41 #elif defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin */
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42 fp_->_p += increment;
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43 fp_->_r -= increment;
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e21211210418 Port the extended stdio functions to emx+gcc.
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44 #elif defined __EMX__ /* emx+gcc */
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45 fp->_ptr += increment;
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46 fp->_rcount -= increment;
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47 #elif defined __minix /* Minix */
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48 fp_->_ptr += increment;
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49 fp_->_count -= increment;
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50 #elif defined _IOERR /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, NonStop Kernel */
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c421fead68d3 Improve freadseek's efficiency after ungetc.
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51 fp_->_ptr += increment;
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52 fp_->_cnt -= increment;
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53 #elif defined __UCLIBC__ /* uClibc */
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54 # ifdef __STDIO_BUFFERS
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55 fp->__bufpos += increment;
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56 # else
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57 abort ();
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58 # endif
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59 #elif defined __QNX__ /* QNX */
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60 fp->_Next += increment;
11236
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61 #elif defined __MINT__ /* Atari FreeMiNT */
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62 fp->__bufp += increment;
16344
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63 #elif defined EPLAN9 /* Plan9 */
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64 fp->rp += increment;
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4611578c5669 Add conditional code for SLOW_BUT_NO_HACKS.
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65 #elif defined SLOW_BUT_NO_HACKS /* users can define this */
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66 #else
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67 #error "Please port gnulib freadseek.c to your platform! Look at the definition of getc, getc_unlocked on your system, then report this to bug-gnulib."
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68 #endif
9826
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69 }
9738
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70
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71 int
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72 freadseek (FILE *fp, size_t offset)
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73 {
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74 size_t total_buffered;
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75 int fd;
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76
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77 if (offset == 0)
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78 return 0;
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79
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80 /* Seek over the already read and buffered input as quickly as possible,
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81 without doing any system calls. */
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82 total_buffered = freadahead (fp);
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83 /* This loop is usually executed at most twice: once for ungetc buffer (if
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84 present) and once for the main buffer. */
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85 while (total_buffered > 0)
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86 {
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87 size_t buffered;
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88
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89 if (freadptr (fp, &buffered) != NULL && buffered > 0)
12421
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90 {
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91 size_t increment = (buffered < offset ? buffered : offset);
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92
12421
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93 freadptrinc (fp, increment);
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94 offset -= increment;
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95 if (offset == 0)
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96 return 0;
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97 total_buffered -= increment;
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98 if (total_buffered == 0)
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99 break;
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100 }
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101 /* Read one byte. If we were reading from the ungetc buffer, this
12421
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102 switches the stream back to the main buffer. */
9826
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103 if (fgetc (fp) == EOF)
12421
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104 goto eof;
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105 offset--;
9738
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106 if (offset == 0)
12421
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107 return 0;
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108 total_buffered--;
9738
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109 }
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110
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111 /* Test whether the stream is seekable or not. */
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112 fd = fileno (fp);
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113 if (fd >= 0 && lseek (fd, 0, SEEK_CUR) >= 0)
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114 {
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115 /* FP refers to a regular file. fseek is most efficient in this case. */
12255
83ddd76ac091 fflush, freadseek: use fseeko, not fseek
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116 return fseeko (fp, offset, SEEK_CUR);
9738
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117 }
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118 else
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119 {
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120 /* FP is a non-seekable stream, possibly not even referring to a file
12421
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121 descriptor. Read OFFSET bytes explicitly and discard them. */
9738
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122 char buf[4096];
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123
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124 do
12421
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125 {
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126 size_t count = (sizeof (buf) < offset ? sizeof (buf) : offset);
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127 if (fread (buf, 1, count, fp) < count)
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128 goto eof;
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129 offset -= count;
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130 }
9738
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131 while (offset > 0);
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132
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133 return 0;
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134 }
9826
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135
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136 eof:
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137 /* EOF, or error before or while reading. */
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138 if (ferror (fp))
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139 return EOF;
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diff changeset
140 else
c421fead68d3 Improve freadseek's efficiency after ungetc.
Bruno Haible <bruno@clisp.org>
parents: 9825
diff changeset
141 /* Encountered EOF. */
c421fead68d3 Improve freadseek's efficiency after ungetc.
Bruno Haible <bruno@clisp.org>
parents: 9825
diff changeset
142 return 0;
9738
923434ebe936 New module 'freadseek'.
Bruno Haible <bruno@clisp.org>
parents:
diff changeset
143 }