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Overview
| Comment: | Use the __builtin_clzll() function of gcc to improve the performance and reduce the size of the sqlite3LogEst() routine. |
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| Downloads: | Tarball | ZIP archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
a42a438cbbd721765ca55e71c464552d |
| User & Date: | drh 2017-08-17 20:53:07.912 |
Context
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2017-08-18
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| 08:29 | Only use indexes on expressions to optimize ORDER BY and GROUP BY if the collation sequence matches. Possible fix for [e20dd54a]. (check-in: 37e1900880 user: dan tags: trunk) | |
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2017-08-17
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| 20:53 | Use the __builtin_clzll() function of gcc to improve the performance and reduce the size of the sqlite3LogEst() routine. (check-in: a42a438cbb user: drh tags: trunk) | |
| 19:23 | Small optimization in the Expr tree walker. (check-in: 264a5e1b75 user: drh tags: trunk) | |
Changes
Changes to src/util.c.
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LogEst sqlite3LogEst(u64 x){
static LogEst a[] = { 0, 2, 3, 5, 6, 7, 8, 9 };
LogEst y = 40;
if( x<8 ){
if( x<2 ) return 0;
while( x<8 ){ y -= 10; x <<= 1; }
}else{
while( x>255 ){ y += 40; x >>= 4; } /*OPTIMIZATION-IF-TRUE*/
while( x>15 ){ y += 10; x >>= 1; }
}
return a[x&7] + y - 10;
}
#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** Convert a double into a LogEst
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LogEst sqlite3LogEst(u64 x){
static LogEst a[] = { 0, 2, 3, 5, 6, 7, 8, 9 };
LogEst y = 40;
if( x<8 ){
if( x<2 ) return 0;
while( x<8 ){ y -= 10; x <<= 1; }
}else{
#if GCC_VERSION>=5004000
int i = 60 - __builtin_clzll(x);
y += i*10;
x >>= i;
#else
while( x>255 ){ y += 40; x >>= 4; } /*OPTIMIZATION-IF-TRUE*/
while( x>15 ){ y += 10; x >>= 1; }
#endif
}
return a[x&7] + y - 10;
}
#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** Convert a double into a LogEst
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