Modulo Bug?

[Peter Alexander]

On Saturday, 11 August 2012 at 13:48:16 UTC, David wrote:
> -1 % 16 = -1
>
> Shouldn't that be 15? It seems like the sign is ignored for the 
> modulo.
>
> Is this a bug or intended behaviour? The Python implementation 
> returns here, as expected, 15.

 From the language spec:

"For integral operands of the / and % operators, the quotient 
rounds towards zero and the remainder has the same sign as the 
dividend."

http://dlang.org/expression.html

In your case, the dividend is -1, so the remainder has the same 
sign (-ve). The quotient rounds towards zero, so in this case the 
quotient is zero, so the remainder must be -1.

Different programming languages handle it differently. In C and 
C++ it is implementation defined! (C++11 makes it the same as in 
D)

See: http://en.wikipedia.org/wiki/Modulo_operation