* rotate_left(): rewrite to help compiler make use of rol insns.

* golden_ratio_hash(): Fix comments.

diff --git a/ginac/utils.h b/ginac/utils.h
index 392efd40b70776437144e5cb8ec1b6983171216b..8a33be0ed6085ebfd32578a53e8560b3eabb8093 100644 (file)
--- a/ginac/utils.h
+++ b/ginac/utils.h
@@ -68,17 +68,14 @@ inline int compare_pointers(const void * a, const void * b)
 /** Rotate bits of unsigned value by one bit to the left. */
 inline unsigned rotate_left(unsigned n)
 {
-       if (n & 0x80000000U)
-               n = n << 1 | 0x00000001U;
-       else
-               n = n << 1;
-       return n;
+       return (n & 0x80000000U) ? (n << 1 | 0x00000001U) : (n << 1);
 }
 
 /** Truncated multiplication with golden ratio, for computing hash values. */
 inline unsigned golden_ratio_hash(unsigned n)
 {
-       // This function requires arithmetic with at least 64 significant bits
+       // This function works much better when fast arithmetic with at
+       // least 64 significant bits is available.
 #if SIZEOF_LONG >= 8
        // So 'long' has 64 bits.  Excellent!  We prefer it because it might be
        // more efficient than 'long long'.
@@ -91,8 +88,8 @@ inline unsigned golden_ratio_hash(unsigned n)
        unsigned long long l = n * 0x4f1bbcddULL;
        return (unsigned)l;
 #else
-       // Do the multiplication manually by splitting n up into the lower and
-       // upper two bytes.
+       // Without a type with 64 significant bits do the multiplication manually
+       // by splitting n up into the lower and upper two bytes.
        const unsigned n0 = (n & 0x0000ffffU);
        const unsigned n1 = (n & 0xffff0000U) >> 16;
        return (n0 * 0x0000bcddU) + ((n1 * 0x0000bcddU + n0 * 0x00004f1bU) << 16);