> Or I guess we could leave this as you've written it and add support
> for a cast from money to numeric.
I tried rewriting my function to use numeric, but I discovered that numeric
division is not exact. (Otherwise SELECT 1::numeric / 3::numeric would result
in an infinite loop.) So I went back to my float8 version and wrote a cast from
money to numeric.
Here is my C source code now:
#include <postgres.h>
#include <fmgr.h>
#include <utils/cash.h>
#include <utils/numeric.h>
#include <utils/pg_locale.h>
PG_MODULE_MAGIC;
extern Datum int8_numeric(PG_FUNCTION_ARGS);
extern Datum numeric_div(PG_FUNCTION_ARGS);
extern Datum numeric_mul(PG_FUNCTION_ARGS);
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);
}
PG_FUNCTION_INFO_V1(cash_numeric);
/* cash_numeric()
* Convert cash to numeric.
*/
Datum
cash_numeric(PG_FUNCTION_ARGS)
{
Cash money = PG_GETARG_CASH(0);
int fpoint;
int64 scale;
int i;
Numeric result;
Datum amount;
Datum numeric_scale;
Datum one;
struct lconv *lconvert = PGLC_localeconv();
/*
* Find the number of digits after the decimal point.
* (These lines were copied from cash_in().)
*/
fpoint = lconvert->frac_digits;
if (fpoint < 0 || fpoint > 10)
fpoint = 2;
scale = 1;
for (i = 0; i < fpoint; i++)
scale *= 10;
amount = DirectFunctionCall1(&int8_numeric, Int64GetDatum(money));
one = DirectFunctionCall1(&int8_numeric, Int64GetDatum(1));
numeric_scale = DirectFunctionCall1(&int8_numeric, Int64GetDatum(scale));
numeric_scale = DirectFunctionCall2(&numeric_div, one, numeric_scale);
result = DatumGetNumeric(DirectFunctionCall2(&numeric_mul, amount,
numeric_scale));
result->n_sign_dscale = NUMERIC_SIGN(result) | fpoint; /* Display the right
number of decimal digits. */
PG_RETURN_NUMERIC(result);
}
------------------------------------------------------------------------------------
And here is the SQL it takes to load it:
CREATE FUNCTION cash_div_cash(money, money) RETURNS double precision
LANGUAGE c IMMUTABLE STRICT
AS '$libdir/divide_money', 'cash_div_cash';
CREATE FUNCTION cash_numeric(money) RETURNS numeric
LANGUAGE c IMMUTABLE STRICT
AS '$libdir/divide_money', 'cash_numeric';
CREATE OPERATOR / (
PROCEDURE = cash_div_cash,
LEFTARG = money,
RIGHTARG = money
);
CREATE CAST (money AS numeric) WITH FUNCTION cash_numeric(money) AS ASSIGNMENT;
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