Inconsistency in integer quotient

[rishikesha]

sage: a=-17
sage: a//4
-5
sage: a.div(4)
-4
sage: a.mod(4)
3

I recommend we redefine

def div(self, other):
    q,_ = self.quo_rem(other)
    return q

Component: basic arithmetic

Issue created by migration from https://trac.sagemath.org/ticket/2579

[rishikesha]

comment:1

sage: a=-17

sage: a//4

-5

sage: a.div(4)

-4

sage: a.mod(4)

3

I recommend we redefine

def div(self, other):

q,_ = self.quo_rem(other) 

return q

[sagetrac-cwitty]

comment:3

If we want a.div(b) to be floor(a/b) (which I agree we probably do, if we want the method to exist at all), the correct fix is to change from mpz_tdiv_qr to mpz_fdiv_q.

[rishikesha]

I think the basis logic should be as below. Since this will make the remainder always positive.

if mpz_sgn(_other.value) == 1:
            mpz_fdiv_q(q.value, _self.value, _other.value)        
else:
            mpz_cdiv_q(q.value, _self.value, _other.value)

[rishikesha]

Attachment: integerdiv.patch.gz

[rishikesha]

comment:5

I used quo_rem to redefine div. I would have essentially copied and pasted quo_rem otherwise.

[mwhansen]

comment:6

Looks good to me.

[sagetrac-mabshoff]

comment:8

Merged in Sage 2.11.alpha0