PostgreSQL has a numeric exp() function and a numeric ln() function, so a numeric pow() function is trivial. pow(A,z) = exp(z*ln(A)) Probably, it could be made a bit more efficient if specially tuned so as to not require these functions. Newton's method (or something of that nature) could obviously be used to write a more generic version. The double C function can provide the starting estimate. > -----Original Message----- > From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general- > owner@xxxxxxxxxxxxxx] On Behalf Of Alvaro Herrera > Sent: Wednesday, May 18, 2005 8:33 PM > To: John Burger > Cc: pgsql-general@xxxxxxxxxxxxxx > Subject: Re: numeric precision when raising one numeric to > another. > > On Wed, May 18, 2005 at 10:46:50PM -0400, John Burger wrote: > > >>Considering that the SQL spec says the result of multiplication of > > >>exact > > >>numeric types is exact numeric types of precision S1+S2, and > > >>exponentiation is nothing more than repeated multiplication, > > > > > >... not when the exponent is non-integral. > > > > For one thing. For another, I believe the standard C library only has > > floating point exponentiation functions, not that there aren't plenty > > of numeric libraries with integral ones. Finally, exponentiated > > numbers get real big, real fast, and the floating point types can hold > > much larger magnitudes than the integer types, albeit inexactly. For > > example, on the Mac I'm using now, long long ints max out at about > > 10^19, while long doubles can represent 10^308. > > Well, we already have an interesting library of mathematical functions > for NUMERIC (which is an arbitrary precision type, so it wouldn't matter > how big the result would get). I think the only reason we don't have a > NUMERIC exponentiation function is that nobody has implemented it. > > -- > Alvaro Herrera (<alvherre[a]surnet.cl>) > "People get annoyed when you try to debug them." (Larry Wall) > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@xxxxxxxxxxxxxx ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
