#7949: Bit-shifts in Z/(n)
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Reporter: spancratz | Owner: spancratz
Type: defect | Status: new
Priority: minor | Milestone: sage-4.3.1
Component: basic arithmetic | Keywords: bit shift, integer mod ring
Work_issues: | Author: spancratz
Upstream: N/A | Reviewer:
Merged: |
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Currently, some code for bit-shifts in Z/(n) looks like
{{{
def __lshift__(IntegerMod_gmp self, int right):
...
cdef IntegerMod_gmp x
x = self._new_c()
mpz_mul_2exp(x.value, self.value, right)
mpz_fdiv_r(x.value, x.value, self.__modulus.sageInteger.value)
return x
}}}
where the method ``mpz_mul_2exp`` expect an ``unsigned long``. Negative
values of ``right`` thus cause undesired integral promotion.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7949>
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