Math

map() [value tranformation]

// EXAMPLE USAGE

// Map an analog value to 8 bits (0 to 255)
void setup() {
  pinMode(D1, OUTPUT);
}

void loop()
{
  int val = analogRead(A0);
  val = map(val, 0, 4095, 0, 255);
  analogWrite(D1, val);
}

Re-maps a number from one range to another. That is, a value of fromLow would get mapped to toLow, a value of fromHigh to toHigh, values in-between to values in-between, etc.

map(value, fromLow, fromHigh, toLow, toHigh);

Does not constrain values to within the range, because out-of-range values are sometimes intended and useful. The constrain() function may be used either before or after this function, if limits to the ranges are desired.

Note that the "lower bounds" of either range may be larger or smaller than the "upper bounds" so the map() function may be used to reverse a range of numbers, for example

y = map(x, 1, 50, 50, 1);

The function also handles negative numbers well, so that this example

y = map(x, 1, 50, 50, -100);

is also valid and works well.

When called with integers, the map() function uses integer math so will not generate fractions, when the math might indicate that it should do so. Fractional remainders are truncated, not rounded.

Parameters can either be integers or floating point numbers:

• value: the number to map
• fromLow: the lower bound of the value's current range
• fromHigh: the upper bound of the value's current range
• toLow: the lower bound of the value's target range
• toHigh: the upper bound of the value's target range

The function returns the mapped value, as integer or floating point depending on the arguments.

Appendix: For the mathematically inclined, here's the whole function

int map(int value, int fromStart, int fromEnd, int toStart, int toEnd)
{
    if (fromEnd == fromStart) {
        return value;
    }
    return (value - fromStart) * (toEnd - toStart) / (fromEnd - fromStart) + toStart;
}