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https://github.com/jart/cosmopolitan.git
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3e4fd4b0ad
This change also pays off some of the remaining technical debt with stdio, file descriptors, and memory managemnt polyfills.
61 lines
3 KiB
C
61 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/calls.h"
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#include "libc/errno.h"
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#include "libc/stdio/stdio.h"
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#include "libc/sysv/consts/o.h"
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/**
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* Repositions open file stream.
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*
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* This function flushes the buffer (unless it's currently in the EOF
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* state) and then calls lseek() on the underlying file. If the stream
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* is in the EOF state, this function can be used to restore it without
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* needing to reopen the file.
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*
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* @param f is a non-null stream handle
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* @param offset is the byte delta
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* @param whence can be SEET_SET, SEEK_CUR, or SEEK_END
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* @returns new offset or -1 on error
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*/
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long fseek(FILE *f, long offset, int whence) {
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int skew;
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int64_t newpos;
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if (f->fd != -1) {
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if (whence == SEEK_CUR && f->beg < f->end) {
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offset -= f->end - f->beg;
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}
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if (f->beg && !f->end) {
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f->writer(f);
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}
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if ((newpos = lseek(f->fd, offset, whence)) != -1) {
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f->state = 0;
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f->beg = 0;
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f->end = 0;
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return newpos;
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} else {
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f->state = errno == ESPIPE ? EBADF : errno;
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return -1;
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}
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} else {
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f->beg = offset % f->size;
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return -1;
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}
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}
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