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Use standard librart sqrt function in pg_stat_statements 

The stddev calculation included a faster but unportable sqrt function.
This is not worth the extra effort, and won't work everywhere. If the
standard library function is good enough for the SQL function it
should be good enough here too.
This commit is contained in:
Andrew Dunstan 2015-03-28 09:22:51 -04:00
parent 3a20b0e7b6
commit cfe12763c3
1 changed files with 2 additions and 19 deletions
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21
contrib/pg_stat_statements/pg_stat_statements.c
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@ -57,6 +57,7 @@
*/
#include "postgres.h"
#include <math.h>
#include <sys/stat.h>
#include <unistd.h>
@ -326,7 +327,6 @@ static char *generate_normalized_query(pgssJumbleState *jstate, const char *quer
int *query_len_p, int encoding);
static void fill_in_constant_lengths(pgssJumbleState *jstate, const char *query);
static int comp_location(const void *a, const void *b);
static inline double sqrtd(const double x);
/*
@ -1583,7 +1583,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
*/
if (tmp.calls > 1)
values[i++] =
Float8GetDatum(sqrtd(tmp.sum_var_time / tmp.calls));
Float8GetDatum(sqrt(tmp.sum_var_time / tmp.calls));
else
values[i++] = Float8GetDatum(0.0);
}
@ -2968,20 +2968,3 @@ comp_location(const void *a, const void *b)
else
return 0;
}
/*
* fast sqrt algorithm: reference from Fast inverse square root algorithms.
*/
static inline double
sqrtd(const double x)
{
double x_half = 0.5 * x;
long long int tmp = 0x5FE6EB50C7B537AAl - ( *(long long int*)&x >> 1);
double x_result = * (double*)&tmp;
x_result *= (1.5 - (x_half * x_result * x_result));
/* If retry this calculation, it becomes higher precision at sqrt */
x_result *= (1.5 - (x_half * x_result * x_result));
return x_result * x;
}