Clean up UTF-8 parsing and use CLZ if available

2 files changed, 34 insertions, 27 deletions

diff --git a/src/writer.c b/src/writer.c
index 6d9055e8..63b8d5af 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -158,42 +158,44 @@ sink(const void* buf, size_t len, SerdWriter* writer)
 	return serd_byte_sink_write(buf, len, &writer->byte_sink);
 }
 
-// Parse a UTF-8 character, set *size to the length, and return the code point
+// Return the number of bytes in a UTF-8 character
 static inline uint32_t
-parse_utf8_char(SerdWriter* writer, const uint8_t* utf8, size_t* size)
+utf8_num_bytes(const uint8_t* utf8)
 {
-	uint32_t c = 0;
 	if ((utf8[0] & 0x80) == 0) {  // Starts with `0'
-		*size = 1;
-		c     = utf8[0];
-	} else if ((utf8[0] & 0xE0) == 0xC0) {  // Starts with `110'
-		*size = 2;
-		c     = utf8[0] & 0x1F;
+		return 1;
+	}
+
+#ifdef HAVE_BUILTIN_CLZ
+	return __builtin_clz(~utf8[0] << 24);
+#else
+	if ((utf8[0] & 0xE0) == 0xC0) {  // Starts with `110'
+		return 2;
 	} else if ((utf8[0] & 0xF0) == 0xE0) {  // Starts with `1110'
-		*size = 3;
-		c     = utf8[0] & 0x0F;
+		return 3;
 	} else if ((utf8[0] & 0xF8) == 0xF0) {  // Starts with `11110'
-		*size = 4;
-		c     = utf8[0] & 0x07;
-	} else {
-		w_err(writer, SERD_ERR_BAD_ARG, "invalid UTF-8: %X\n", utf8[0]);
-		*size = 0;
-		return 0;
+		return 4;
 	}
+	return 0;
+#endif
+}
 
-	size_t  i  = 0;
-	uint8_t in = utf8[i++];
-
-#define READ_BYTE() \
-	in = utf8[i++] & 0x3F; \
-	c  = (c << 6) | in;
-
-	switch (*size) {
-	case 4: READ_BYTE();
-	case 3: READ_BYTE();
-	case 2: READ_BYTE();
+// Parse a UTF-8 character, set *size to the length, and return the code point
+static inline uint32_t
+parse_utf8_char(SerdWriter* writer, const uint8_t* utf8, size_t* size)
+{
+	switch (*size = utf8_num_bytes(utf8)) {
+	case 1: case 2: case 3: case 4:
+		break;
+	default:
+		return 0;
 	}
 
+	uint32_t c = utf8[0] & ((1 << (8 - *size)) - 1);
+	for (size_t i = 1; i < *size; ++i) {
+		const uint8_t in = utf8[i] & 0x3F;
+		c = (c << 6) | in;
+	}
 	return c;
 }
 
diff --git a/wscript b/wscript
index b39e43a8..3d60859c 100644
--- a/wscript
+++ b/wscript
@@ -78,6 +78,11 @@ def configure(conf):
                    defines       = ['_POSIX_C_SOURCE=200809L'],
                    mandatory     = False)
 
+    conf.check(fragment      = 'int main() { return __builtin_clz(1); }',
+               function_name = '__builtin_clz',
+               define_name   = 'HAVE_BUILTIN_CLZ',
+               mandatory     = False)
+
     autowaf.define(conf, 'SERD_VERSION', SERD_VERSION)
     autowaf.set_lib_env(conf, 'serd', SERD_VERSION)
     conf.write_config_header('serd_config.h', remove=False)