1 files changed, 97 insertions, 0 deletions
diff --git a/src/unicode.cpp b/src/unicode.cpp
index 83aa8deef..e33fb793b 100644
--- a/src/unicode.cpp
+++ b/src/unicode.cpp
@@ -65,3 +65,100 @@ bool rune_is_whitespace(Rune r) {
 	}
 	return false;
 }
+
+
+gb_global u8 const global__utf8_first[256] = {
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x00-0x0F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x10-0x1F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x20-0x2F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x30-0x3F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x40-0x4F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x50-0x5F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x60-0x6F
+	0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, // 0x70-0x7F
+	0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, // 0x80-0x8F
+	0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, // 0x90-0x9F
+	0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, // 0xA0-0xAF
+	0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, // 0xB0-0xBF
+	0xf1, 0xf1, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, // 0xC0-0xCF
+	0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, // 0xD0-0xDF
+	0x13, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x23, 0x03, 0x03, // 0xE0-0xEF
+	0x34, 0x04, 0x04, 0x04, 0x44, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, 0xf1, // 0xF0-0xFF
+};
+
+typedef struct Utf8AcceptRange {
+	u8 lo, hi;
+} Utf8AcceptRange;
+
+gb_global Utf8AcceptRange const global__utf8_accept_ranges[] = {
+	{0x80, 0xbf},
+	{0xa0, 0xbf},
+	{0x80, 0x9f},
+	{0x90, 0xbf},
+	{0x80, 0x8f},
+};
+
+
+isize utf8_decode(u8 const *str, isize str_len, Rune *codepoint_out) {
+	isize width = 0;
+	Rune codepoint = GB_RUNE_INVALID;
+
+	if (str_len > 0) {
+		u8 s0 = str[0];
+		u8 x = global__utf8_first[s0], sz;
+		u8 b1, b2, b3;
+		Utf8AcceptRange accept;
+		if (x >= 0xf0) {
+			Rune mask = (cast(Rune)x << 31) >> 31;
+			codepoint = (cast(Rune)s0 & (~mask)) | (GB_RUNE_INVALID & mask);
+			width = 1;
+			goto end;
+		}
+		if (s0 < 0x80) {
+			codepoint = s0;
+			width = 1;
+			goto end;
+		}
+
+		sz = x&7;
+		accept = global__utf8_accept_ranges[x>>4];
+		if (str_len < gb_size_of(sz))
+			goto invalid_codepoint;
+
+		b1 = str[1];
+		if (b1 < accept.lo || accept.hi < b1)
+			goto invalid_codepoint;
+
+		if (sz == 2) {
+			codepoint = (cast(Rune)s0&0x1f)<<6 | (cast(Rune)b1&0x3f);
+			width = 2;
+			goto end;
+		}
+
+		b2 = str[2];
+		if (!gb_is_between(b2, 0x80, 0xbf))
+			goto invalid_codepoint;
+
+		if (sz == 3) {
+			codepoint = (cast(Rune)s0&0x1f)<<12 | (cast(Rune)b1&0x3f)<<6 | (cast(Rune)b2&0x3f);
+			width = 3;
+			goto end;
+		}
+
+		b3 = str[3];
+		if (!gb_is_between(b3, 0x80, 0xbf))
+			goto invalid_codepoint;
+
+		codepoint = (cast(Rune)s0&0x07)<<18 | (cast(Rune)b1&0x3f)<<12 | (cast(Rune)b2&0x3f)<<6 | (cast(Rune)b3&0x3f);
+		width = 4;
+		goto end;
+
+	invalid_codepoint:
+		codepoint = GB_RUNE_INVALID;
+		width = 1;
+	}
+
+end:
+	if (codepoint_out) *codepoint_out = codepoint;
+	return width;
+}