Document integer pragma effect on % operator

Jon Orwant <orwant@media.mit.edu> writes:

> Of course I expect "use integer" to use integers for everything.  
> I don't see why that should change the value of -534 % 210.  
> 
> Here's what perlmod says:
>  
>    Binary "%" computes the modulus of two numbers.  Given integer operands $a
>    and $b: If $b is positive, then $a % $b is $a minus the largest multiple of
>    $b that is not greater than $a.  If $b is negative, then $a % $b is $a
>    minus the smallest multiple of $b that is not less than $a (i.e. the result
>    will be less than or equal to zero).
> 
> $a is -534.  $b is 210.  The largest multiple of 210 not greater than -534
> is -630.  Ergo, -534 % 210 is -534 - -630, or 96.  
> 
> But if you "use integer", you get -114.  Arithmetic Most Foul.

I think it should stay the way it is.  Perhaps we should apply this
documentation patch.

p5p-msgid: m3yawjmzhx.fsf@furu.g.aas.no

1 files changed, 5 insertions, 0 deletions

diff --git a/pod/perlop.pod b/pod/perlop.pod
index e4088ec9c4..538745dd6a 100644
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -186,6 +186,11 @@ C<$a>.  If C<$b> is negative, then C<$a % $b> is C<$a> minus the
 smallest multiple of C<$b> that is not less than C<$a> (i.e. the
 result will be less than or equal to zero).
 
+Note than when C<use integer> is in scope "%" give you direct access
+to the modulus operator as implemented by your C compiler.  This
+operator is not as well defined for negative operands, but it will
+execute faster.
+
 Binary "x" is the repetition operator.  In a scalar context, it
 returns a string consisting of the left operand repeated the number of
 times specified by the right operand.  In a list context, if the left