auto import from //depot/cupcake/@135843
diff --git a/libc/stdlib/strtoumax.c b/libc/stdlib/strtoumax.c
new file mode 100644
index 0000000..ec45377
--- /dev/null
+++ b/libc/stdlib/strtoumax.c
@@ -0,0 +1,115 @@
+/* $OpenBSD: strtoumax.c,v 1.1 2006/01/13 17:58:09 millert Exp $ */
+
+/*-
+ * Copyright (c) 1992 The Regents of the University of California.
+ * All rights reserved.
+ *
+ * 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 <ctype.h>
+#include <errno.h>
+#include <inttypes.h>
+
+/*
+ * Convert a string to a uintmax_t.
+ *
+ * Ignores `locale' stuff. Assumes that the upper and lower case
+ * alphabets and digits are each contiguous.
+ */
+uintmax_t
+strtoumax(const char *nptr, char **endptr, int base)
+{
+ const char *s;
+ uintmax_t acc, cutoff;
+ int c;
+ int neg, any, cutlim;
+
+ /*
+ * See strtoq for comments as to the logic used.
+ */
+ s = nptr;
+ do {
+ c = (unsigned char) *s++;
+ } while (isspace(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')) {
+ c = s[1];
+ s += 2;
+ base = 16;
+ }
+ if (base == 0)
+ base = c == '0' ? 8 : 10;
+
+ /* BIONIC: avoid division and modulo for common cases */
+#define CASE_BASE(x) \
+ case x: cutoff = UINTMAX_MAX / x; \
+ cutlim = UINTMAX_MAX % x; \
+ break
+
+ switch (base) {
+ CASE_BASE(8);
+ CASE_BASE(10);
+ CASE_BASE(16);
+ default:
+ cutoff = UINTMAX_MAX / base;
+ cutlim = UINTMAX_MAX % base;
+ }
+
+ for (acc = 0, any = 0;; c = (unsigned char) *s++) {
+ if (isdigit(c))
+ c -= '0';
+ else if (isalpha(c))
+ c -= isupper(c) ? 'A' - 10 : 'a' - 10;
+ else
+ break;
+ if (c >= base)
+ break;
+ if (any < 0)
+ continue;
+ if (acc > cutoff || (acc == cutoff && c > cutlim)) {
+ any = -1;
+ acc = UINTMAX_MAX;
+ errno = ERANGE;
+ } else {
+ any = 1;
+ acc *= (uintmax_t)base;
+ acc += c;
+ }
+ }
+ if (neg && any > 0)
+ acc = -acc;
+ if (endptr != 0)
+ *endptr = (char *) (any ? s - 1 : nptr);
+ return (acc);
+}