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diff --git a/Build/source/texk/kpathsea/line.c b/Build/source/texk/kpathsea/line.c
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+/* line.c: return the next line from a file, or NULL.
+
+ Copyright 1992, 1993, 1995, 1996, 2008, 2013, 2014, 2020 Karl Berry.
+ Copyright 1998, 1999, 2001, 2005 Olaf Weber.
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with this library; if not, see <http://www.gnu.org/licenses/>. */
+
+#include <kpathsea/config.h>
+#include <kpathsea/line.h>
+
+#ifdef WIN32
+#undef getc
+#undef ungetc
+#define getc win32_getc
+#define ungetc win32_ungetc
+#define FLOCKFILE(x)
+#define FUNLOCKFILE(x)
+
+#else /* not WIN32 */
+/* By POSIX, getc() has to be thread-safe, which means (un)locking on
+ every character read. It is much faster to lock the stream (once),
+ use getc_unlocked to read, and then unlock the stream. We need to be
+ thread-safe especially for the sake of MPlib.
+
+ Perhaps we will be lucky enough to be able to do this
+ unconditionally, without checking in configure. We'll see. */
+#undef getc
+#define getc getc_unlocked
+#define FLOCKFILE(x) flockfile(x)
+#define FUNLOCKFILE(x) funlockfile(x)
+#endif /* not WIN32 */
+
+/* Allocate in increments of this size. */
+#define BLOCK_SIZE 75
+
+char *
+read_line (FILE *f)
+{
+ int c;
+ unsigned limit = BLOCK_SIZE;
+ unsigned loc = 0;
+ char *line = xmalloc (limit);
+
+ FLOCKFILE (f);
+
+ while ((c = getc (f)) != EOF && c != '\n' && c != '\r') {
+ /* Silently drop null bytes. */
+ if (c == 0) {
+ continue;
+ }
+
+ line[loc] = c;
+ loc++;
+
+ /* By testing after the assignment, we guarantee that we'll always
+ have space for the null we append below. We know we always
+ have room for the first char, since we start with BLOCK_SIZE. */
+ if (loc == limit) {
+ limit += BLOCK_SIZE;
+ line = xrealloc (line, limit);
+ }
+ }
+
+ /* If we read anything, return it, even a partial last-line-if-file
+ which is not properly terminated. */
+ if (loc == 0 && c == EOF) {
+ /* At end of file. */
+ free (line);
+ line = NULL;
+ } else {
+ /* Terminate the string. We can't represent nulls in the file,
+ but this doesn't matter. */
+ line[loc] = 0;
+ /* Absorb LF of a CRLF pair. */
+ if (c == '\r') {
+ c = getc (f);
+ if (c != '\n') {
+ ungetc (c, f);
+ }
+ }
+ }
+
+ FUNLOCKFILE (f);
+
+ return line;
+}