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7.27 Power Function

The following functions are equivalent to the function gsl_pow_int (see Small integer powers) with an error estimate. These functions are declared in the header file gsl_sf_pow_int.h.

— Function: double gsl_sf_pow_int (double x, int n)
— Function: int gsl_sf_pow_int_e (double x, int n, gsl_sf_result * result)

These routines compute the power x^n for integer n. The power is computed using the minimum number of multiplications. For example, x^8 is computed as ((x^2)^2)^2, requiring only 3 multiplications. For reasons of efficiency, these functions do not check for overflow or underflow conditions. 

     #include <gsl/gsl_sf_pow_int.h>
     /* compute 3.0**12 */
     double y = gsl_sf_pow_int(3.0, 12);