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MDEV-19787 Speedup Table_map_iterator, via compiler intrinsics

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Use __builtin_ctzll on GCC/Clang and _BitScanForward/_BitScanForward64 on
MSVC to speed up Table_map_iterator::next_bit(), up to 3 times in benchmarks
This commit is contained in:
Vladislav Vaintroub
2019-06-17 15:50:59 +01:00
parent 4594d68d10
commit 16ac8404ac
2 changed files with 50 additions and 18 deletions
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27
sql/sql_bitmap.h
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@ -27,29 +27,20 @@
#include <my_bitmap.h>
#include <my_bit.h>
/* An iterator to quickly walk over bits in unlonglong bitmap. */
/* An iterator to quickly walk over bits in ulonglong bitmap. */
class Table_map_iterator
{
ulonglong bmp;
uint no;
public:
Table_map_iterator(ulonglong t) : bmp(t), no(0) {}
int next_bit()
Table_map_iterator(ulonglong t): bmp(t){}
uint next_bit()
{
static const char last_bit[16] = { 32, 0, 1, 0,
2, 0, 1, 0,
3, 0, 1, 0,
2, 0, 1, 0 };
uint bit;
while ((bit= last_bit[bmp & 0xF]) == 32)
{
no += 4;
bmp= bmp >> 4;
if (!bmp)
return BITMAP_END;
}
bmp &= ~(1LL << bit);
return no + bit;
if (!bmp)
return BITMAP_END;
uint bit= my_find_first_bit(bmp);
bmp &= ~(1ULL << bit);
return bit;
}
int operator++(int) { return next_bit(); }
enum { BITMAP_END= 64 };