## Names:

doubledouble, DD represents a number as the sum of two IEEE doubles.

## Library names:

sollya_obj_t sollya_lib_double_double(sollya_obj_t) sollya_obj_t sollya_lib_double_double_obj() int sollya_lib_is_double_double_obj(sollya_obj_t) sollya_obj_t sollya_lib_build_function_double_double(sollya_obj_t) #define SOLLYA_DD(x) sollya_lib_build_function_double_double(x)

## Description:

• doubledouble is both a function and a constant.
• As a function, it rounds its argument to the nearest number that can be written as the sum of two double precision numbers.
• The algorithm used to compute doubledouble(x) is the following: let xh = double(x) and let xl = double(x - xh). Return the number xh + xl. Note that if the current precision is not sufficient to exactly represent xh + xl, a rounding will occur and the result of doubledouble(x) will be useless.
• As a constant, it symbolizes the double-double precision format. It is used in contexts when a precision format is necessary, e.g. in the commands round, roundcoefficients and implementpoly. See the corresponding help pages for examples.

## Example 1:

> verbosity=1!;
> a = 1+ 2^(-100);
> DD(a);
Warning: For at least 1 of the constants displayed in decimal, rounding has happened.
1.0000000000000000000000000000007888609052210118054
> prec=50!;
> DD(a);
1.0000000000000000000000000000007888609052210118054117285652827862296732064351090230047702789306640625