1 files changed, 47 insertions, 0 deletions
diff --git a/src/multibyte/decode.c b/src/multibyte/decode.c
new file mode 100644
index 00000000..8d3d3c0b
--- /dev/null
+++ b/src/multibyte/decode.c
@@ -0,0 +1,47 @@
+/* 
+ * This code was written by Rich Felker in 2010; no copyright is claimed.
+ * This code is in the public domain. Attribution is appreciated but
+ * unnecessary.
+ */
+
+#include <stdlib.h>
+#include <inttypes.h>
+#include <wchar.h>
+#include <errno.h>
+
+#include "internal.h"
+
+/* Decodes UTF-8 byte-by-byte. The c argument must be initialized to 0
+ * to begin decoding; when finished it will contain the Unicode scalar
+ * value decoded. Return value is 1 if finished, 0 if in-progress, and
+ * -1 if an invalid sequence was encountered. After an invalid sequence,
+ * the state (in c) automatically resets to 0 if a continuation byte was
+ * expected to facilitate a calling idiom of immediately retrying a
+ * failed decode call after processing the invalid sequence. If the
+ * second try fails, the byte is invalid as a starter as well.
+ *
+ * A trivial usage idiom is:
+ *       while (src<end && (n=decode(dst, *src))>=0) 1[dst+=n]=0, src++;
+ */
+
+int decode(unsigned *c, unsigned b)
+{
+	if (!*c) {
+		if (b < 0x80) {
+			*c = b;
+			return 1;
+		} else if (b-SA >= SB-SA) {
+			*c = FAILSTATE;
+			return -1;
+		}
+		*c = bittab[b-SA];
+		return 0;
+	}
+
+	if (OOB(*c,b)) {
+		*c = 0;
+		return -1;
+	}
+	*c = *c<<6 | b-0x80;
+	return !(*c&(1U<<31));
+}