Re: dividing money by money

On Mar 31, 2010, at 7:07 AM, Kevin Grittner wrote:

> (I was going to mark the TODO as an easy one.)

I thought it would be pretty simple, too, so I decided to go ahead and write and test it as an external module.

I think the function definition could be pasted directly into an appropriate place in src/backend/utils/adt/cash.c, if someone wants to add it to the main code base. The SQL to load it would need to be modified somewhat to fit into postgres.bki.

Here is the C source:

#include <postgres.h>
#include <fmgr.h>
#include <utils/cash.h>

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(cash_div_cash);

/* cash_div_cash()
* Divide cash by cash, returning float8.
*/
Datum
cash_div_cash(PG_FUNCTION_ARGS)
{
Cash dividend = PG_GETARG_CASH(0);
Cash divisor = PG_GETARG_CASH(1);
float8 quotient;

if (divisor == 0)
ereport(ERROR,
(errcode(ERRCODE_DIVISION_BY_ZERO),
errmsg("division by zero")));

quotient = (float8)dividend / (float8)divisor;
PG_RETURN_FLOAT8(quotient);
}

-------------------------------------------------------------------------------------

And here is the SQL to load it (assuming it has been compiled as a dynamically loadable module named divide_money and placed in the library directory on the server):

CREATE FUNCTION cash_div_cash(money, money) RETURNS double precision
LANGUAGE c IMMUTABLE
AS '$libdir/divide_money', 'cash_div_cash';

CREATE OPERATOR / (
PROCEDURE = cash_div_cash,
LEFTARG = money,
RIGHTARG = money
);