diff --git a/lib/libc/strtoull.c b/lib/libc/strtoull.c
new file mode 100644
index 0000000..2e65a43
--- /dev/null
+++ b/lib/libc/strtoull.c
@@ -0,0 +1,112 @@
+/*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 1992, 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 long integer.
+ *
+ * Assumes that the upper and lower case
+ * alphabets and digits are each contiguous.
+ */
+unsigned long long strtoull(const char *nptr, char **endptr, int base)
+{
+	const char *s;
+	unsigned long long acc;
+	char c;
+	unsigned long long cutoff;
+	int neg, any, cutlim;
+
+	/*
+	 * See strtoq 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 = ULLONG_MAX / base;
+	cutlim = ULLONG_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 = ULLONG_MAX;
+	} else if (neg)
+		acc = -acc;
+	if (endptr != NULL)
+		*endptr = (char *)(any ? s - 1 : nptr);
+	return (acc);
+}