CODEWITHSUNDEEP
perlmodulo
Chas. Owens
Chas. Owens

Reputation: 64909

Is the behavior of % with negative operands defined in Perl 5?

Until recently (i.e. C99), the behavior of the modulo operator was implementation defined in C. Since Perl 5 is written in C, is it reliant on the behavior of the C compiler used to build it?

Upvotes: 5

Views: 722

Answers (2)

brian d foy
brian d foy

Reputation: 132773

Perl implements its own modulo operator, but you can get to the one from your C compiler by using the integer pragma. perlop says

Note that when use integer is in scope, "%" gives you direct access to the modulo operator as implemented by your C compiler. This operator is not as well defined for negative operands, but it will execute faster.

That is, you have to be careful when you are using integer because the modulo might give you different answers.

Upvotes: 2

Chas. Owens
Chas. Owens

Reputation: 64909

No, Perl 5 defines the modulo operator in perlop and even has tests to ensure it works as documented.

from perl/t/op/arith.t

tryeq $T++,  13 %  4, 1;
tryeq $T++, -13 %  4, 3;
tryeq $T++,  13 % -4, -3;
tryeq $T++, -13 % -4, -1;

However, if you use the integer pragma, you are at the mercies of the C compiler.

Upvotes: 10

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