GNU Scientific Library – Reference Manual: Small integer powers

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### 4.4 Small integer powers

A common complaint about the standard C library is its lack of a function for calculating (small) integer powers. GSL provides some simple functions to fill this gap. For reasons of efficiency, these functions do not check for overflow or underflow conditions.

Function: double gsl_pow_int (double x, int n)
Function: double gsl_pow_uint (double x, unsigned int n)

  These routines computes the power x^n for integer n. The power is computed efficiently—for example, x^8 is computed as ((x^2)^2)^2, requiring only 3 multiplications. A version of this function which also computes the numerical error in the result is available as `gsl_sf_pow_int_e`.

Function: double gsl_pow_2 (const double x)
Function: double gsl_pow_3 (const double x)
Function: double gsl_pow_4 (const double x)
Function: double gsl_pow_5 (const double x)
Function: double gsl_pow_6 (const double x)
Function: double gsl_pow_7 (const double x)
Function: double gsl_pow_8 (const double x)
Function: double gsl_pow_9 (const double x)

  These functions can be used to compute small integer powers x^2, x^3, etc. efficiently. The functions will be inlined when `HAVE_INLINE` is defined, so that use of these functions should be as efficient as explicitly writing the corresponding product expression.

    #include <gsl/gsl_math.h>
    double y = gsl_pow_4 (3.141)  /* compute 3.141**4 */