lib/charset: add u16_strlcat() function

Provide u16 string version of strlcat().

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

include/charset.h

@@ -261,6 +261,20 @@ u16 *u16_strcpy(u16 *dest, const u16 *src);
  */
 u16 *u16_strdup(const void *src);
 
+/**
+ * u16_strlcat() - Append a length-limited, %NUL-terminated string to another
+ *
+ * Append the source string @src to the destination string @dest, overwriting
+ * null word at the end of @dest adding  a terminating null word.
+ *
+ * @dest:		zero terminated u16 destination string
+ * @src:		zero terminated u16 source string
+ * @count:		size of buffer in u16 words including taling 0x0000
+ * Return:		required size including trailing 0x0000 in u16 words
+ *			If return value >= count, truncation occurred.
+ */
+size_t u16_strlcat(u16 *dest, const u16 *src, size_t size);
+
 /**
  * utf16_to_utf8() - Convert an utf16 string to utf8
  *

lib/charset.c

@@ -416,6 +416,22 @@ u16 *u16_strdup(const void *src)
 	return new;
 }
 
+size_t u16_strlcat(u16 *dest, const u16 *src, size_t count)
+{
+	size_t destlen = u16_strlen(dest);
+	size_t srclen = u16_strlen(src);
+	size_t ret = destlen + srclen + 1;
+
+	if (destlen >= count)
+		return ret;
+	if (ret > count)
+		srclen -= ret - count;
+	memcpy(&dest[destlen], src, 2 * srclen);
+	dest[destlen + srclen] = 0x0000;
+
+	return ret;
+}
+
 /* Convert UTF-16 to UTF-8.  */
 uint8_t *utf16_to_utf8(uint8_t *dest, const uint16_t *src, size_t size)
 {