The error handling form of the special functions always calculate an
error estimate along with the value of the result. Therefore,
structures are provided for amalgamating a value and error estimate.
These structures are declared in the header file ``gsl_sf_result.h'`.

The `gsl_sf_result`

struct contains value and error fields.

typedef struct { double val; double err; } gsl_sf_result;

The field `val` contains the value and the field `err` contains
an estimate of the absolute error in the value.

In some cases, an overflow or underflow can be detected and handled by a
function. In this case, it may be possible to return a scaling exponent
as well as an error/value pair in order to save the result from
exceeding the dynamic range of the built-in types. The
`gsl_sf_result_e10`

struct contains value and error fields as well
as an exponent field such that the actual result is obtained as
`result * 10^(e10)`

.

typedef struct { double val; double err; int e10; } gsl_sf_result_e10;

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