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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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41
include/my_bit.h
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@ -130,6 +130,47 @@ static inline uchar last_byte_mask(uint bits)
/* Return bitmask for the significant bits */
return ((2U << used) - 1);
}
#ifdef _MSC_VER
#include <intrin.h>
#endif
#define MY_FIND_FIRST_BIT_END sizeof(ulonglong)*8
/*
Find the position of the first(least significant) bit set in
the argument. Returns 64 if the argument was 0.
*/
static inline uint my_find_first_bit(ulonglong n)
{
if(!n)
return MY_FIND_FIRST_BIT_END;
#if defined(__GNUC__)
return __builtin_ctzll(n);
#elif defined(_MSC_VER)
#if defined(_M_IX86)
unsigned long bit;
if( _BitScanForward(&bit, (uint)n))
return bit;
_BitScanForward(&bit, (uint)(n>>32));
return bit + 32;
#else
unsigned long bit;
_BitScanForward64(&bit, n);
return bit;
#endif
#else
/* Generic case */
uint shift= 0;
static const uchar 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[(n >> shift) & 0xF]) == 32)
shift+= 4;
return shift+bit;
#endif
}
C_MODE_END
#endif /* MY_BIT_INCLUDED */

27
sql/sql_bitmap.h
View File

@ -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 };