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diff --git a/lib/libc/strtoul.c b/lib/libc/strtoul.c
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+/*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 1990, 1993
+ * The Regents of the University of California. All rights reserved.
+ *
+ * Copyright (c) 2011 The FreeBSD Foundation
+ * All rights reserved.
+ * Portions of this software were developed by David Chisnall
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+/*
+ * Convert a string to an unsigned long integer.
+ *
+ * Assumes that the upper and lower case
+ * alphabets and digits are each contiguous.
+ */
+unsigned long strtoul(const char *nptr, char **endptr, int base)
+{
+ const char *s;
+ unsigned long acc;
+ char c;
+ unsigned long cutoff;
+ int neg, any, cutlim;
+
+ /*
+ * See strtol for comments as to the logic used.
+ */
+ s = nptr;
+ do {
+ c = *s++;
+ } while (isspace((unsigned char)c));
+ if (c == '-') {
+ neg = 1;
+ c = *s++;
+ } else {
+ neg = 0;
+ if (c == '+')
+ c = *s++;
+ }
+ if ((base == 0 || base == 16) &&
+ c == '0' && (*s == 'x' || *s == 'X') &&
+ ((s[1] >= '0' && s[1] <= '9') ||
+ (s[1] >= 'A' && s[1] <= 'F') ||
+ (s[1] >= 'a' && s[1] <= 'f'))) {
+ c = s[1];
+ s += 2;
+ base = 16;
+ }
+ if (base == 0)
+ base = c == '0' ? 8 : 10;
+ acc = any = 0;
+
+ cutoff = ULONG_MAX / base;
+ cutlim = ULONG_MAX % base;
+ for ( ; ; c = *s++) {
+ if (c >= '0' && c <= '9')
+ c -= '0';
+ else if (c >= 'A' && c <= 'Z')
+ c -= 'A' - 10;
+ else if (c >= 'a' && c <= 'z')
+ c -= 'a' - 10;
+ else
+ break;
+ if (c >= base)
+ break;
+ if (any < 0 || acc > cutoff || (acc == cutoff && c > cutlim))
+ any = -1;
+ else {
+ any = 1;
+ acc *= base;
+ acc += c;
+ }
+ }
+ if (any < 0) {
+ acc = ULONG_MAX;
+ } else if (neg)
+ acc = -acc;
+ if (endptr != NULL)
+ *endptr = (char *)(any ? s - 1 : nptr);
+ return (acc);
+}