wow! i have optimized str_len_uns() yet more :-) now it is not slowed

down when a 0x80 byte is present.  a slight simple change.

diff --git a/lib/hashfunc.c b/lib/hashfunc.c
index 980b4077f673b339386ed7a30e0b4e696d818531..2f951c6977ab5725e49281fa5135bfcb4d9d4592 100644 (file)
--- a/lib/hashfunc.c
+++ b/lib/hashfunc.c
@@ -37,19 +37,21 @@ hashfunc_init(void)
 static inline uns CONST
 str_len_uns(uns x)
 {
-       const uns sub = ((uns) -1) / 0xff;
+       const uns sub = ~0U / 0xff;
        const uns and = sub * 0x80;
        uns a, i;
        byte *bytes;
-       a = (x ^ (x - sub)) & and;
+       a = ~x & (x - sub) & and;
        /* 
         * x_2 = x - 0x01010101;
-        * x_3 = x ^ x_2;
+        * x_3 = ~x & x_2;
         * a = x_3 & 0x80808080;
         *
-        * If no byte of x is in {0, 0x80}, then the highest bit of each byte
-        * of x_2 is the same as of x.  Hence x_3 has all these highest bits
-        * cleared.  If a == 0, then we are sure there is no zero byte in x.
+        * If all bytes of x are nonzero, then the highest bit of each byte of
+        * x_2 is lower or equal to the corresponding bit of x.  Hence x_3 has
+        * all these highest bits cleared (the target bit is set iff the source
+        * bit has changed from 0 to 1).  If a == 0, then we are sure there is
+        * no zero byte in x.
         */
        if (!a)
                return sizeof(uns);