Add functions for encoding/decoding UTF-8/16

These will be needed to implement wide string literals.

1 files changed, 80 insertions, 0 deletions

diff --git a/utf.c b/utf.c
new file mode 100644
index 0000000..a8f5a49
--- /dev/null
+++ b/utf.c
@@ -0,0 +1,80 @@
+#include <uchar.h>
+#include "utf.h"
+
+size_t
+utf8enc(char32_t c, char *s)
+{
+	if (c < 0x80) {
+		s[0] = c;
+		return 1;
+	}
+	if (c < 0x800) {
+		s[0] = 0xc0 | c >> 6;
+		s[1] = 0x80 | c & 0x3f;
+		return 2;
+	}
+	if (c < 0xd800 || c - 0xe000 < 0x2000) {
+		s[0] = 0xe0 | c >> 12;
+		s[1] = 0x80 | c >> 6 & 0x3f;
+		s[2] = 0x80 | c & 0x3f;
+		return 3;
+	}
+	if (c - 0x10000 < 0x100000) {
+		s[0] = 0xf0 | c >> 18;
+		s[1] = 0x80 | c >> 12 & 0x3f;
+		s[2] = 0x80 | c >> 6 & 0x3f;
+		s[3] = 0x80 | c & 0x3f;
+		return 4;
+	}
+	return -1;
+}
+
+size_t
+utf8dec(const char *s, size_t n, char32_t *c)
+{
+	size_t i, l;
+	unsigned char b;
+	char32_t x;
+
+	b = s[0];
+	if (b < 0x80) {
+		*c = b;
+		return 1;
+	}
+	if ((b & 0xe0) == 0xc0) {
+		x = b & 0x1f;
+		l = 2;
+	} else if ((b & 0xf0) == 0xe0) {
+		x = b & 0x0f;
+		l = 3;
+	} else if ((b & 0xf8) == 0xf0) {
+		x = b & 0x07;
+		l = 4;
+	}
+	if (n < l)
+		return -1;
+	for (i = 1; i < l; ++i) {
+		b = *++s;
+		if ((b & 0xc0) != 0x80)
+			return -1;
+		x = x << 6 | b & 0x3f;
+	}
+	*c = x;
+	return l;
+}
+
+size_t
+utf16enc(char32_t c, char16_t *s)
+{
+	if (c < 0xd800 || c - 0xe000 < 0x2000) {
+		s[0] = c;
+		return 1;
+	}
+	c -= 0x10000;
+	if (c < 0x100000) {
+		s[0] = 0xd800 | c >> 10 & 0x3ff;
+		s[1] = 0xdc00 | c & 0x3ff;
+		return 2;
+	}
+	return -1;
+}