c++ - Optimal way to choose less or greater operator before loop -

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i have 2 arrays comprising x,y vales y=f(x). provide function finds value of x corresponds either min or max sampled value of y.

what efficient way select proper comparison operator before looping on values in arrays?

for example, following:

double findextremum(const double* x, const double* y,                     const unsigned int n, const bool ismin) {    static std::less<double>    lt;    static std::greater<double> gt;    std::binary_function<double,double,bool>& isbeyond = ismin ? lt : gt;    double xm(*x), ym(*y);    (unsigned int i=0; i<n; ++i, ++x, ++y) {       if (isbeyond()(*y,ym)) {          ym = *y;          xm = *x;      }    } }

unfortunately, base class std::binary_function not define virtual operator().

will compiler g++ 4.8 able optimize straight forward implementation?

double findextremum(const double* x, const double* y,                     const unsigned int n, const bool ismin) {    double xm(*x), ym(*y);    (unsigned int i=0; i<n; ++i, ++x, ++y) {       if ( ( ismin && (*y<ym)) ||            (!ismin && (*y>ym)) ) {          ym = *y;          xm = *x;      }    } }

is there way arrange things make easy compiler optimize? there known algorithm doing this?

i prefer avoid using templated function, if possible.

you need pass comparison functor templated function parameter, e.g.

template <typename compare> double findextremum(const double* x, const double* y,                     const unsigned int n, compare compare) {    double xm(*x), ym(*y);    (unsigned int i=0; i<n; ++i, ++x, ++y) {       if (compare(*y,ym)) {          ym = *y;          xm = *x;      }    } }

then if need runtime choice, write this:

if (ismin) {     findextremum(x, y, n, std::less<double>()); } else {     findextremum(x, y, n, std::greater<double>()); }

avoiding templated function not possible in case. best performing code 1 embeds comparison operation directly in loop, avoiding function call - can either write template or write 2 copies of function. templated function better solution.


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