Re: 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.