Hi,
tested x86_64-linux, committed to mainline. See audit trail for details...
Thanks,
Paolo.
/////////////////////
2011-09-06 Paolo Carlini <[email protected]>
PR libstdc++/50257
* include/bits/hashtable_policy.h (_Prime_rehash_policy::
_M_next_bkt): Optimize for small argument.
Index: include/bits/hashtable_policy.h
===================================================================
--- include/bits/hashtable_policy.h (revision 178574)
+++ include/bits/hashtable_policy.h (working copy)
@@ -427,8 +427,15 @@
_Prime_rehash_policy::
_M_next_bkt(std::size_t __n) const
{
- const unsigned long __p = *std::lower_bound(__prime_list, __prime_list
- + _S_n_primes, __n);
+ // Optimize lookups involving the first elements of __prime_list.
+ // (useful to speed-up, eg, constructors)
+ static const unsigned char __fastbkt[12]
+ = { 2, 2, 2, 3, 5, 5, 7, 7, 11, 11, 11, 11 };
+
+ const unsigned long __p
+ = __n <= 11 ? __fastbkt[__n]
+ : *std::lower_bound(__prime_list + 5,
+ __prime_list + _S_n_primes, __n);
_M_next_resize =
static_cast<std::size_t>(__builtin_floor(__p * _M_max_load_factor));
return __p;
