lib: provide function hextoull()

We often convert hexadecimal strings to hextoull(). Provide a wrapper
function to simple_strtoull() that does not require specifying the radix.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/include/vsprintf.h b/include/vsprintf.h
index fe95147..9da6ce7 100644
--- a/include/vsprintf.h
+++ b/include/vsprintf.h
@@ -45,6 +45,19 @@
 unsigned long hextoul(const char *cp, char **endp);
 
 /**
+ * hex_strtoull - convert a string in hex to an unsigned long long
+ *
+ * @cp: The string to be converted
+ * @endp: Updated to point to the first character not converted
+ * Return: value decoded from string (0 if invalid)
+ *
+ * Converts a hex string to an unsigned long long. If there are invalid
+ * characters at the end these are ignored. In the worst case, if all characters
+ * are invalid, 0 is returned
+ */
+unsigned long long hextoull(const char *cp, char **endp);
+
+/**
  * dec_strtoul - convert a string in decimal to an unsigned long
  *
  * @cp: The string to be converted
diff --git a/lib/strto.c b/lib/strto.c
index f83ac67..206d1e9 100644
--- a/lib/strto.c
+++ b/lib/strto.c
@@ -78,6 +78,11 @@
 	return simple_strtoul(cp, endp, 16);
 }
 
+unsigned long long hextoull(const char *cp, char **endp)
+{
+	return simple_strtoull(cp, endp, 16);
+}
+
 ulong dectoul(const char *cp, char **endp)
 {
 	return simple_strtoul(cp, endp, 10);