* Include the operators.h header file in the source files, not in ex.h.

[ginac.git] / ginac / utils.h

diff --git a/ginac/utils.h b/ginac/utils.h
index a161ee2bdf02390d4e406684d39f49be9435daae..8a33be0ed6085ebfd32578a53e8560b3eabb8093 100644 (file)
--- a/ginac/utils.h
+++ b/ginac/utils.h
@@ -65,46 +65,34 @@ inline int compare_pointers(const void * a, const void * b)
        return 0;
 }
 
-/** Rotate lower 31 bits of unsigned value by one bit to the left
- *  (upper bit gets cleared). */
-inline unsigned rotate_left_31(unsigned n)
+/** Rotate bits of unsigned value by one bit to the left. */
+inline unsigned rotate_left(unsigned n)
 {
-       // clear highest bit and shift 1 bit to the left
-       n = (n & 0x7FFFFFFFU) << 1;
-       
-       // overflow? clear highest bit and set lowest bit
-       if (n & 0x80000000U)
-               n = (n & 0x7FFFFFFFU) | 0x00000001U;
-       
-       GINAC_ASSERT(n<0x80000000U);
-       
-       return n;
+       return (n & 0x80000000U) ? (n << 1 | 0x00000001U) : (n << 1);
 }
 
-/** Golden ratio hash function for the 31 least significant bits. */
+/** 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'.
-       unsigned long l = n * 0x4f1bbcddL;
-       return (l & 0x7fffffffU) ^ (l >> 32);
+       unsigned long l = n * 0x4f1bbcddUL;
+       return (unsigned)l;
 #elif SIZEOF_LONG_LONG >= 8
        // This requires 'long long' (or an equivalent 64 bit type)---which is,
        // unfortunately, not ANSI-C++-compliant.
        // (Yet C99 demands it, which is reason for hope.)
-       unsigned long long l = n * 0x4f1bbcddL;
-       return (l & 0x7fffffffU) ^ (l >> 32);
-#elif SIZEOF_LONG_DOUBLE > 8
-       // If 'long double' is bigger than 64 bits, we assume that the mantissa
-       // has at least 64 bits. This is not guaranteed but it's a good guess.
-       // Unfortunately, it may lead to horribly slow code.
-       const static long double golden_ratio = .618033988749894848204586834370;
-       long double m = golden_ratio * n;
-       return unsigned((m - int(m)) * 0x80000000);
+       unsigned long long l = n * 0x4f1bbcddULL;
+       return (unsigned)l;
 #else
-#error "No 64 bit data type. You lose."
+       // 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);
 #endif
 }