Given two ranges, [a1,a2] and [b1,b2]; then a value s in range [a1,a2] is linearly mapped to a value t in range [b1,b2] when:
The task is to write a function/subroutine/… that takes two ranges and a real number, and returns the mapping of the real number from the first to the second range. Use this function to map values from the range [0, 10]
to the range [-1, 0]
.
This example defines a template function to handle the mapping, using two std::pair objects to define the source and destination ranges. It returns the provided value mapped into the target range.
It’s not written efficiently; certainly, there can be fewer explicit temporary variables. The use of the template offers a choice in types for precision and accuracy considerations, though one area for improvement might be to allow a different type for intermediate calculations.
#include <iostream> #include <utility> template<typename tVal> tVal map_value(std::pair<tVal,tVal> a, std::pair<tVal, tVal> b, tVal inVal) { tVal inValNorm = inVal - a.first; tVal aUpperNorm = a.second - a.first; tVal normPosition = inValNorm / aUpperNorm; tVal bUpperNorm = b.second - b.first; tVal bValNorm = normPosition * bUpperNorm; tVal outVal = b.first + bValNorm; return outVal; } int main() { std::pair<float,float> a(0,10), b(-1,0); for(float value = 0.0; 10.0 >= value; ++value) std::cout << "map_value(" << value << ") = " << map_value(a, b, value) << std::endl; return 0; }
Output:
map_value(0) = -1 map_value(1) = -0.9 map_value(2) = -0.8 map_value(3) = -0.7 map_value(4) = -0.6 map_value(5) = -0.5 map_value(6) = -0.4 map_value(7) = -0.3 map_value(8) = -0.2 map_value(9) = -0.1 map_value(10) = 0
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