The result could be up to 8 limbs, which is why you should allocate 8
limbs for c. The top limb might turn out to be zero of course.
The easiest way to print the result is to use gmp_printf with the %N
option for mpn's. You need to also give it the number of limbs, as
documented on pages 67-68 of our documentation.
Bill.
On 23 November 2012 00:55, mgundes <mg...@hotmail.com> wrote:
>
> Hi,
>
> I am not good at arithmetic but I need to calculate multiplication of big
> numbers. I will try to explain my need:
>
> For instance, if I have two 128 bit numbers represented with arrays below:
>
> unsigned int a[4] = {100, 20, 30, 40};
> unsigned int b[4] = {200, 10, 5, 120};
> unsigned int c[4] = {0,0,0,0};
>
> I want to multiply a and b, then assign the result to the c:
>
> mpn_mul_n((mp_limb_t *)c, (const mp_limb_t *)a, (const mp_limb_t *)b,
> 4);
>
> Since mpn_mul takes result pointer as mp_limb_t type, then what if result
> exceeds? I mean the result of two integer multiplication probably exceeds
> integer size. Is there any example for multiplication of big numbers? I
> tried mpn_mul_n() as above and used mpn_get_str to see the result but I
> guess I could not use correctly.
>
> Kind regards,
> Thanks
>
> --
> MahmutG
>
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