efi_loader: carve out utf_to_cp()

Carve out a function to translate a Unicode code point to an 8bit codepage.

Provide a unit test for the new function.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/charset.c

@@ -10,6 +10,7 @@
 #include <capitalization.h>
 #include <cp437.h>
 #include <efi_loader.h>
+#include <errno.h>
 #include <malloc.h>
 
 /**
@@ -472,3 +473,30 @@ uint8_t *utf16_to_utf8(uint8_t *dest, const uint16_t *src, size_t size)
 
 	return dest;
 }
+
+/**
+ * utf_to_cp() - translate Unicode code point to 8bit codepage
+ *
+ * Codepoints that do not exist in the codepage are rendered as question mark.
+ *
+ * @c:		pointer to Unicode code point to be translated
+ * @codepage:	Unicode to codepage translation table
+ * Return:	0 on success, -ENOENT if codepoint cannot be translated
+ */
+int utf_to_cp(s32 *c, const u16 *codepage)
+{
+	if (*c >= 0x80) {
+		int j;
+
+		/* Look up codepage translation */
+		for (j = 0; j < 0x80; ++j) {
+			if (*c == codepage[j]) {
+				*c = j + 0x80;
+				return 0;
+			}
+		}
+		*c = '?';
+		return -ENOENT;
+	}
+	return 0;
+}