One problem is that you are using unsigned int, instead of mp_limb_t
(which is probably unsigned long or unsigned long long on your
machine).
Bill.
On 23 November 2012 13:12, mgundes <mg...@hotmail.com> wrote:
>
> 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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>
>
>
> --
> MahmutG
>
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