integer operations

wannabeboy has asked for the wisdom of the Perl Monks concerning the following question:

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Re: integer operations by Thilosophy (Curate) on Mar 01, 2005 at 09:49 UTC
Try `ceil` in the POSIX module: `use POSIX qw(ceil); print ceil (15/2);` [download] For positive numbers `int(15/2) + 1` probably also works, but the docs for `int` discourage this use. Update: Actually, `int(15/2) + 1` will not work very well at all, because `int(14/2)+1` also produces `8`, whereas you want `7` (I guess). Sorry to have brought it up...	[reply] [d/l] [select]
Re: integer operations by Jasper (Chaplain) on Mar 01, 2005 at 10:23 UTC
Rounding function, I did a search for 'rounding' Edit by BazB: fix link to node.	[reply]
Re: integer operations by ambrus (Abbot) on Mar 01, 2005 at 18:58 UTC
POSIX::ceil is the solution, but if you know that the numerator is always an integer, and the denominator is a positive integer, then you can use this too: `$numerator = 15; $denominator = 2; print int(($numerator $denominator + - 1) / $denominator), $/;` [download] or `$numerator = 15; $denominator = 2; print do{ use integer; ($numerator ++ $denominator - 1) / $denominator }, $/;` [download]	[reply] [d/l] [select]
Re: integer operations by DrHyde (Prior) on Mar 01, 2005 at 10:09 UTC
There's also the `integer` pragma. You don't want it in this case because it will throw away the 0.5 giving you 7, but I expect some other monks looking at this will find it useful: `$ perl -Minteger -e 'print 15/2' 7` [download]	[reply] [d/l] [select]
Re^2: integer operations by tphyahoo (Vicar) on Mar 01, 2005 at 10:30 UTC
obvious but... `perl -Minteger -e 'print 15/2 + 1'` [download] prints 8... or `use strict; use warnings; my $eight = int (15 / 2 ) +1; print $eight;` [download]	[reply] [d/l] [select]
Re^3: integer operations by Jasper (Chaplain) on Mar 01, 2005 at 11:53 UTC
Untested: `my @integers = 1..50000; print $integer[15/2];` [download] Yes, I'm just being silly. Also, this won't work for negative numbers. At all.	[reply] [d/l]
Re: integer operations by Roy Johnson (Monsignor) on Mar 01, 2005 at 14:14 UTC
Here's a little ceiling function, if you don't feel like using POSIX: `sub ceil { my $n = shift; int($n) + ($n > int($n)); }` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^2: integer operations by DrHyde (Prior) on Mar 02, 2005 at 09:28 UTC
Why would anyone not want to `use POSIX`? It's a core module, and is damned useful. It's also woefully underused.	[reply] [d/l]
Re^3: integer operations by Anonymous Monk on Mar 02, 2005 at 10:02 UTC
Indeed. Writing your own is more typing, and it's slower as well. About the only reason I can think of is wanting to avoid the loading of POSIX. But if that's significant, you probably want to inline your ceiling functionality anyway. `#!/usr/bin/perl use strict; use warnings; use POSIX 'ceil'; use Benchmark 'cmpthese'; sub my_ceil { my $n = shift; int($n) + ($n > int($n)) } our @tries = map {-100 + rand 50} 1 .. 1_000; cmpthese -1, { ceil => '@a = map { ceil($_)} @tries', own => '@b = map {my_ceil($_)} @tries', inline => '@c = map {int($_) + ($_ > int($_))} @tries', }; __END__ Rate own ceil inline own 355/s -- -52% -54% ceil 737/s 107% -- -4% inline 767/s 116% 4% --` [download]	[reply] [d/l]