Le vendredi 31 juillet 2015 10:16:10 UTC+2, Bill Hart a écrit :
>
>
>
> On 30 July 2015 at 22:10, <20100.d...@gmail.com <javascript:>> wrote:
>
>> Thanks for the answer! (and sorry for my very late reply)
>>
>> Le dimanche 3 mai 2015 18:54:43 UTC+2, Bill Hart a écrit :
>>>
>>>
>>>
>>> On 3 May 2015 at 12:51, <20100.d...@gmail.com> wrote:
>>>
>>>> Hello,
>>>>
>>>> I would like to know whether it it is possible to compare a mpz_t and a
>>>> mpq_t more efficiently than:
>>>> - creating a mpq_t with denominator 1
>>>> - swap the numerator with the mpz_t
>>>> - call mpq_cmp
>>>> - swap back the numerator with the mpz_t
>>>> - free the memory of the mpq_t
>>>>
>>>
>>> Sure. Take a look at the mpq_numref and mpq_denref functions. There is
>>> no need to create an mpq_t, though you do need a temporary mpz_t for the
>>> result of the multiplication.
>>>
>>> Of course, any function which performed such a comparison would have to
>>> create this internally anyway. So in terms of efficiency, it's about the
>>> best you can do. You can special case denominator = 1 or numerator = 0 and
>>> a few other cases like that. But it's about the best you can do.
>>>
>>
>> I asked the question after I had a look at mpq_cmp. This function first
>> tries some comparison based on the size of numerators and denominators. So
>> I deduced that calling mpq_cmp would be faster (in simple cases) rather
>> than direct cross multiplication even if I had to initialize an mpq_t with
>> a denominator 1.
>>
>>
>>>> If not, would it be useful to have this as a standalone function (like
>>>> "mpq_cmp_mpz")? There is a need within Sage [1,2] where often integer and
>>>> rational types are mixed.
>>>>
>>>
>>> I'd be inclined to just add such a thing as a macro if you need it
>>> often. It's only about four lines to implement.
>>>
>>
>> What would be this macro? Calling mpq_cmp? Cross multiplication?
>>
>
> Yes, I intended cross multiplication.
>
> You can special case it for denominator = 1, perhaps.
>
Pull request for a new function mpq_cmp_mpz at
https://github.com/wbhart/mpir/pull/157
It is essentially a copy/paste of mpq_cmp with a lot of simplification
since one denominator is just one.
Vincent
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