From aa36d4df21113a36c2e368e0abb417480a6eebbd Mon Sep 17 00:00:00 2001 From: kosaki Date: Thu, 3 Feb 2011 16:54:52 +0000 Subject: * string.c (count_utf8_lead_bytes_with_word): wrote function comments. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30778 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- string.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'string.c') diff --git a/string.c b/string.c index 6628eb0aef..96b5d9cc7f 100644 --- a/string.c +++ b/string.c @@ -1038,13 +1038,30 @@ rb_enc_strlen_cr(const char *p, const char *e, rb_encoding *enc, int *cr) #ifdef NONASCII_MASK #define is_utf8_lead_byte(c) (((c)&0xC0) != 0x80) + +/* + * UTF-8 leading bytes have either 0xxxxxxx or 11xxxxxx + * bit represention. (see http://en.wikipedia.org/wiki/UTF-8) + * Therefore, following pseudo code can detect UTF-8 leading byte. + * + * if (!(byte & 0x80)) + * byte |= 0x40; // turn on bit6 + * return ((byte>>6) & 1); // bit6 represent it's leading byte or not. + * + * This function calculate every bytes in the argument word `s' + * using the above logic concurrently. and gather every bytes result. + */ static inline VALUE count_utf8_lead_bytes_with_word(const VALUE *s) { VALUE d = *s; + + /* Transform into bit0 represent UTF-8 leading or not. */ d |= ~(d>>1); d >>= 6; d &= NONASCII_MASK >> 7; + + /* Gather every bytes. */ d += (d>>8); d += (d>>16); #if SIZEOF_VALUE == 8 -- cgit v1.2.3