/*
- * Hyper-super-meta-alt-control-shift extra fast str_len() and hash_*()
- * routines
+ * UCW Library -- Hyper-super-meta-alt-control-shift extra fast
+ * str_len() and hash_*() routines
*
* It is always at least as fast as the classical strlen() routine and for
* strings longer than 100 characters, it is substantially faster.
*
* (c) 2002, Robert Spalek <robert@ucw.cz>
+ *
+ * This software may be freely distributed and used according to the terms
+ * of the GNU Lesser General Public License.
*/
#include "lib/lib.h"
/* The number of bits the hash in the function hash_*() is rotated by after
* every pass. It should be prime with the word size. */
-#define SHIFT_BITS 5
+#define SHIFT_BITS 7
/* A bit-mask which clears higher bytes than a given threshold. */
static uns mask_higher_bits[sizeof(uns)];
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);