Unroll the loop in decode_utf8() to improve perf

diff --git a/eglib/src/giconv.c b/eglib/src/giconv.c
index 824d72dc4ae6c4621a80c01327fc0facfc6bb6c3..7a413c08d073fc808f617f5325c5c897593de33d 100644 (file)
--- a/eglib/src/giconv.c
+++ b/eglib/src/giconv.c
@@ -501,47 +501,54 @@ decode_utf8 (char **inbytes, size_t *inbytesleft, gunichar *outchar)
 {
        unsigned char *inptr = (unsigned char *) *inbytes;
        size_t inleft = *inbytesleft;
-       size_t i, len = 0;
-       unsigned char c;
        gunichar u;
+       size_t n;
        
-       c = *inptr++;
+       u = *inptr++;
        
-       if (c < 0x80) {
+       if (u < 0x80) {
                /* simple ascii case */
-               len = 1;
-       } else if (c < 0xe0) {
-               c &= 0x1f;
-               len = 2;
-       } else if (c < 0xf0) {
-               c &= 0x0f;
-               len = 3;
-       } else if (c < 0xf8) {
-               c &= 0x07;
-               len = 4;
-       } else if (c < 0xfc) {
-               c &= 0x03;
-               len = 5;
-       } else if (c < 0xfe) {
-               c &= 0x01;
-               len = 6;
+               *inbytesleft = inleft - 1;
+               *inbytes = (char *) inptr;
+               *outchar = u;
+               return 0;
+       } else if (u < 0xc2) {
+               errno = EILSEQ;
+               return -1;
+       } else if (u < 0xe0) {
+               u &= 0x1f;
+               n = 2;
+       } else if (u < 0xf0) {
+               u &= 0x0f;
+               n = 3;
+       } else if (u < 0xf8) {
+               u &= 0x07;
+               n = 4;
+       } else if (u < 0xfc) {
+               u &= 0x03;
+               n = 5;
+       } else if (u < 0xfe) {
+               u &= 0x01;
+               n = 6;
        } else {
                errno = EILSEQ;
                return -1;
        }
        
-       if (len > inleft) {
+       if (n > inleft) {
                errno = EINVAL;
                return -1;
        }
        
-       u = c;
-       for (i = 1; i < len; i++) {
-               u = (u << 6) | ((*inptr) & 0x3f);
-               inptr++;
+       switch (n) {
+       case 6: u = (u << 6) | (*inptr++ ^ 0x80);
+       case 5: u = (u << 6) | (*inptr++ ^ 0x80);
+       case 4: u = (u << 6) | (*inptr++ ^ 0x80);
+       case 3: u = (u << 6) | (*inptr++ ^ 0x80);
+       case 2: u = (u << 6) | (*inptr++ ^ 0x80);
        }
        
-       *inbytesleft = inleft - len;
+       *inbytesleft = inleft - n;
        *inbytes = (char *) inptr;
        *outchar = u;