/*
 autoscale  V1.1
 Scales a variable from one range of numbers to another range using linear interpolation
 Paul Badger 2007
 Modified from code by Greg Shakar

 autoscale takes five parameters all integers, negative numbers will work with all parameters

 originaMin - the minimum value of the original range - this MUST be less than origninalMax
 originalMax - the maximum value of the original range - this MUST be greater than orginalMin

 newBegin - the end of the new range which maps to orginalMin - it can be smaller, or larger, than newEnd, to facilitate inverting the ranges
 newEnd - the end of the new range which maps to originalMax  - it can be larger, or smaller, than newBegin, to facilitate inverting the ranges

 inputValue - the variable for input that will mapped to the given ranges, this variable will be constrained to originaMin <= inputValue <= originalMax

 */

int j;
long scaledResult;

void setup() {
  Serial.begin(9600);
}

void loop(){    // all this does is tests the function
  for ( j=-60; j < 100; j++){
    scaledResult = autoScale( -50, 75, 50, -50, j);

    Serial.print(j, DEC);  
    Serial.print("    ");  
    Serial.println(scaledResult , DEC);
  }  
}

int autoScale( int originalMin, int originalMax, int newBegin, int
newEnd, int inputValue){

  long zeroRefOriginalMax = 0;
  long zeroRefnewEnd = 0;
  long zeroRefCurVal = 0;
  long rangedValue = 0;
  boolean invFlag = 0;

  // Check for out of range inputValues
  if (inputValue < originalMin) {
    inputValue = originalMin;
  }
  if (inputValue > originalMax) {
    inputValue = originalMax;
  }

  // Zero Refference the values
  zeroRefOriginalMax = originalMax - originalMin;

  if (newEnd > newBegin){
    zeroRefnewEnd = newEnd - newBegin;
  }
  else
  {
    zeroRefnewEnd = newBegin - newEnd;
    invFlag = 1;
  }

  zeroRefCurVal = inputValue - originalMin;


 // Check for originalMin > originalMax  - the math for all other cases i.e. negative numbers seems to work out fine
  if (originalMin > originalMax ) {
    return 0;
  }

   if (invFlag == 0){
    rangedValue =  ((zeroRefCurVal * zeroRefnewEnd) /
      zeroRefOriginalMax) + newBegin ;
  }
  else     // invert the ranges
  {  
    rangedValue =  newBegin - ((zeroRefCurVal * zeroRefnewEnd) /
      zeroRefOriginalMax)  ;
  }

  return rangedValue;
}