Re: Proper monetary rounding

The built-in sprintf implements round-to-even already:

for (qw(1.0049 1.0050 1.0051 1.0149 1.0150 1.0151 1.0249 1.0250 1.0251
+)) {
  printf "%s => %0.2f\n", $_, $_;
}
...
1.0049 => 1.00
1.0050 => 1.00
1.0051 => 1.01
1.0149 => 1.01
1.0150 => 1.01
1.0151 => 1.02
1.0249 => 1.02
1.0250 => 1.02
1.0251 => 1.03
[download]

Hmm. Why didn't that work? {grin}

-- Randal L. Schwartz, Perl hacker

Comment on Re: Proper monetary rounding Download Code

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Re^2: Proper monetary rounding by blogical (Pilgrim) on Mar 05, 2007 at 03:43 UTC
That's what I had been doing, until I heard that accountants are actually picky about this sort of thing. "Round to even" considers the case where the number just past the least significant is a 5, followed only by zeroes. It then rounds odd LSDs up to the nearest even, rounding off even LSDs.	[reply]
Re: Proper monetary rounding by jonadab (Parson) on Mar 05, 2007 at 12:49 UTC
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` [download] "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? -- We're working on a six-year set of freely redistributable Vacation Bible School materials.	[reply] [d/l]
Re^2: Proper monetary rounding by monarch (Priest) on Mar 05, 2007 at 16:00 UTC
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.	[reply]
Re: Proper monetary rounding by jonadab (Parson) on Mar 06, 2007 at 16:29 UTC
Re^2: Proper monetary rounding by eric256 (Parson) on Mar 05, 2007 at 18:35 UTC
`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? ___________ Eric Hodges	[reply] [d/l]