Re: [HACKERS] Warning!!

Should I add this to the TODO list?

> "Thomas G. Lockhart" <lockhart(at)alumni(dot)caltech(dot)edu> writes:
> > tgl=> select cash_mul_flt8('$1', '123.77');
> > cash_mul_flt8
> > -------------
> > $123.76
> > (1 row)
> > That's annoying; it's non-symmetric too.
>
> And hardware-dependent, evidently, because I get the right thing on HP:
>
> play=> select cash_mul_flt8('$1', '123.77');
> cash_mul_flt8
> -------------
> $123.77
> (1 row)
>
>
> > The money type is stored as an
> > integer, and the float type is an IEEE double; looks like we have an LSB
> > rounding problem. Not sure what to do about it other than remove the
> > function, which isn't desirable I'm sure...
>
> What's needed is explicit rounding. Instead of letting the compiler do
> the rounding during its implicit float-to-int conversion (which
> generally truncates towards 0 or towards -infinity), do
>
> *** cash.c~ Wed Nov 4 10:11:57 1998
> --- cash.c Wed Nov 4 10:13:06 1998
> ***************
> *** 17,22 ****
> --- 17,23 ----
> #include <limits.h>
> #include <ctype.h>
> #include <locale.h>
> + #include <math.h>
>
> #include "postgres.h"
> #include "miscadmin.h"
> ***************
> *** 419,425 ****
> if (!PointerIsValid(result = palloc(sizeof(Cash))))
> elog(ERROR, "Memory allocation failed, can't multiply cash", NULL);
>
> ! *result = ((*f) * (*c));
>
> return result;
> } /* cash_mul_flt8() */
> --- 420,426 ----
> if (!PointerIsValid(result = palloc(sizeof(Cash))))
> elog(ERROR, "Memory allocation failed, can't multiply cash", NULL);
>
> ! *result = floor((*f) * (*c) + 0.5);
>
> return result;
> } /* cash_mul_flt8() */
>
>
> (Alternatively you could do it with rint(), although I distrust rint()
> because it's context-dependent...)
>
> The other cash functions also need to be looked at for rounding
> sloppiness, so I see no point in committing this fix by its lonesome.
>
> Lessee, who's the author of cash.c ... looks like it's D'Arcy ...
> D'Arcy, you wanna put this on your to-do list?
>
> regards, tom lane
>
>

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