Remap a number from one range to another range. For example, remap celsius to fahrenheit or remap kilometres to miles.

remapper.js

// To remap a value x in range [a, b] to [c, d], we can use:
//
//      y = (x - a) * ((d - c) / (b - a)) + c
//

function remapper(x, a, b, c, d) {
  let y = (x - a) * ((d - c) / (b - a)) + c;
  return y;
}

// Examples:
function celsiusToFahrenheit(celsius) {
  return remapper(celsius, 0, 100, 32, 212);
}

// In C, C++ or Java:
// double remapper(double x, double a, double b, double c, double d) {
//   double y = (x - a) * ((d - c) / (b - a)) + c;
//   return y;
// }