Hi Bill, thanks for reply.
I run simple code below for different lengths of array muıltiplication
and I got weird results with gmp_printf(). I also printed c array and it
seems true but printed result is weird. What is wrong or missing in
function below?
int main() {
unsigned int a[4] = {100, 20, 30, 40};
unsigned int b[4] = {200, 10, 5, 120};
unsigned int c[8];
memset(c, 0, 8 * sizeof(unsigned int));
mpn_mul((mp_limb_t *) c,
(mp_limb_t *) a, 1,
(mp_limb_t *) b, 1);
for (int i=0; i<8; i++)
printf("c[%d]: %u\n", i, c[i]);
gmp_printf("\nresult: %Nu\n\n\n", c, 8);
memset(c, 0, 8 * sizeof(unsigned int));
mpn_mul((mp_limb_t *) c,
(mp_limb_t *) a, 2,
(mp_limb_t *) b, 3);
for (int i=0; i<8; i++)
printf("c[%d]: %u\n", i, c[i]);
gmp_printf("\nresult: %Nu\n\n\n", c, 8);
memset(c, 0, 8 * sizeof(unsigned int));
mpn_mul((mp_limb_t *) c,
(mp_limb_t *) a, 4,
(mp_limb_t *) b, 4);
for (int i=0; i<8; i++)
printf("c[%d]: %u\n", i, c[i]);
gmp_printf("\nresult: %Nu\n\n\n", c, 8);
return 0;
}
Kind Regards,
Thanks
MahmutG
On Fri, Nov 23, 2012 at 3:09 AM, Bill Hart <goodwillh...@googlemail.com>wrote:
> 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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--
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