Re: [HACKERS] pow support for pgbench

Hello,

Sorry for the confusion, I wasn't aware that SQL pow changed types depending on the input value.

Indeed, this is quite strange...

  fabien=# SELECT i, POW(2, i) FROM generate_series(-2, 2) AS i;
   -2 | 0.25
   -1 | 0.5
    0 | 1
    1 | 2
    2 | 4

I've modified the function to match more closely the behaviour of SQL, except that 0^(negative) returns 'double inf'. Do you think there is any value in raising an error instead?

  fabien=# SELECT POW(0,-1);
  ERROR:  zero raised to a negative power is undefined

Hmmmm... I'm fine with double inf, because exception in pgbench means the end of the script, which is not desirable for benchmarking purposes.

I think that:

 - you can simplify the ipow function by removing handling of y<0 case,
   maybe add an assert to be sure to avoid it.

 - you should add more symmetry and simplify the evaluation:

   if (int & int)
   {
      i1, i2 = ...;
      if (i2 >= 0)
        setIntValue(retval, ipow(i1, i2));
      else
        // conversion is done by C, no need to coerce again
        setDoubleValue(retval, pow(i1, i2));
   }
   else
   {
     d1, d2 = ...;
     setDoubleValue(retval, pow(d1, d2));
   }

Add a test case to show what happens on NULL arguments, hopefully the result is NULL.

--
Fabien.