Re: Proper monetary rounding

[jonadab]

in reply to Re^2: Proper monetary rounding
in thread Proper monetary rounding

I think he's saying that sprintf actually does that, in just that way:

perl -e 'my $x = 1.5050; my $y = 1.5150; my $s = sprintf "%0.2f\n%0.2f
+\n", $x, $y; print $s;'
1.50
1.52

"Normal" (gradeschool) rounding would produce 1.51 and 1.52 there, but sprintf says 1.50 and 1.52, which seems an aweful lot like round-to-even to me. How does it differ from what you wanted?

As far as accountants being picky about this... have you ever seen the movie Superman 3?

[monarch]

Are you sure that's sprintf behaviour, or is there a limitation in the IEEE floating point representation of 1.5050 that has it leaning on the low side of 0.0050? That's the only explanation I can think of as to why sprintf would be broken like this.

[jonadab]

Are you sure that's sprintf behaviour, or is there a limitation in the IEEE floating point representation of 1.5050 that has it leaning on the low side of 0.0050?

I'm not personally sure of any of this, no. As far as I know it could depend on the C compiler perl was compiled with, the C library it was compiled against, and the day of the week it was compiled. I was just asking how the other poster's explanation of sprintf's behavior differed from the desired rounding behavior.

On closer inspection, I think I see a difference I didn't notice before, though.

[eric256]

printf("%0.2f\n", $_) for 1.4050, 1.5050, 1.6050, 1.7050; seems to indicate this only works for 1.5... or am i missing a bigger picture here?