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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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libc/calls/hefty/filecmp.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/alg/alg.h"
#include "libc/bits/safemacros.h"
#include "libc/calls/calls.h"
#include "libc/errno.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/madv.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/prot.h"
static void *filecmp$mmap(int fd, size_t size) {
return size ? mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0) : NULL;
}
/**
* Compares contents of files with memcmp().
*
* @return ≤0, 0, or ≥0 based on comparison; or ≠0 on error, in which
* case we make our best effort to sift failing filenames rightward,
* and errno can be set to 0 beforehand to differentiate errors
*/
int filecmp(const char *pathname1, const char *pathname2) {
int res, olderr;
int fd1 = -1;
int fd2 = -1;
char *addr1 = MAP_FAILED;
char *addr2 = MAP_FAILED;
size_t size1 = 0;
size_t size2 = 0;
if ((fd1 = open(pathname1, O_RDONLY)) != -1 &&
(fd2 = open(pathname2, O_RDONLY)) != -1 &&
(size1 = getfiledescriptorsize(fd1)) != -1 &&
(size2 = getfiledescriptorsize(fd2)) != -1 &&
(addr1 = filecmp$mmap(fd1, size1)) != MAP_FAILED &&
(addr2 = filecmp$mmap(fd2, size2)) != MAP_FAILED) {
olderr = errno;
madvise(addr1, size1, MADV_WILLNEED | MADV_SEQUENTIAL);
madvise(addr2, size2, MADV_WILLNEED | MADV_SEQUENTIAL);
errno = olderr;
res = memcmp(addr1, addr2, min(size1, size2));
if (!res && size1 != size2) {
char kNul = '\0';
if (size1 > size2) {
res = cmpub(addr1 + size2, &kNul);
} else {
res = cmpub(addr2 + size1, &kNul);
}
}
} else {
res = cmpuq(&fd1, &fd2) | 1;
}
olderr = errno;
munmap(addr1, size1);
munmap(addr2, size2);
close(fd1);
close(fd2);
errno = olderr;
return res;
}