Have Geek Brain

MPFR rounding 0.9999 to 1?

I am trying to store the value 0.9999 in the mpfr_t variable using the mpfr_set_str () function

But 0.9999 is rounded to 1 (or some other value! = 0.9999) during storage, regardless of the rounded value (GMP_RNDD, GMP_RNDU, GMP_RNDN, GMP_RNDZ)

So what's the best way to store 0.9999 in the mpfr_t variable using mpfr_set_str ()? Is it possible?

Here is my test program, it prints "buffer is: 1" instead of the desired "buffer is: 0.9999":

int main()
{

    size_t precision = 4;
    mpfr_t mpfrValue;

    mpfr_init2(mpfrValue, precision);
    mpfr_set_str(mpfrValue, "0.9999", 10, GMP_RNDN);

    char *buffer = (char*)malloc((sizeof(char) * precision) + 3);
    mp_exp_t exponent;

    mpfr_get_str(buffer,
                 &exponent,
                 10,
                 precision,
                 mpfrValue,
                 GMP_RNDN);

    printf("buffer is: %s\n", buffer);

    free(buffer);
    mpfr_clear(mpfrValue);

    return 0;
}

thanks for the help

+2


a source to share


1 answer


the precision is given in bits , not decimal digits as you seem to assume. It seems that you can retype the correct value up to 4 decimal digits with 15 bit precision. Alternatively, you can print directly using mpfr_printf.

If you need to use mpfr_get_str I would pass null as the first parameter. If you do this, the line will be highlighted for you. Then, to free it, you call mpfr_free_str.



int main()
{
    size_t precision = 15;
    mpfr_t mpfrValue;

    mpfr_init2(mpfrValue, precision);
    mpfr_set_str(mpfrValue, "0.9999", 10, GMP_RNDN);

    mpfr_printf("Value is: %Rf\n", mpfrValue);
    mpfr_clear(mpfrValue);
    return 0;
}
+3


a source






More articles:


All Articles