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//! Temperature conversion table and lookup function

type TempPair = (u16, u16);

// this table contains a pair of temperatures and their 
// corresponding resistance values for a PT100 thermometer
// The first entry of each pair is the temperature multiplied by 10,
// while the second entry contains the temperature at that resistance
// value multiplied by 10, i.e. at 0 deg C, the probe should have a resistance
// of 100 ohms
static LOOKUP_TABLE : &[TempPair]= &[
    (0, 10000),
    (1000, 10390),
    (2000, 10779),
    (3000, 11167),
    (4000, 11554),
    (5000, 11940),
    (6000, 12324),
    (7000, 12708),
    (8000, 13090),
    (9000, 13471),
    (10000, 13851),
    (11000, 14229),
    (12000, 14607),
    (13000, 14983),
];


/// Convert the specified PT100 resistance value into a temperature.
/// 
/// # Arguments
/// 
/// * `val` - A 16 bit unsigned integer specifying the resistance in Ohms multiplied by 100, e.g. 
///           13851 would indicate 138.51 Ohms and convert to 100 degrees Celcius.
/// 
/// # Remarks
/// 
/// The output temperature will be in degrees Celcius multiplied by 100, e.g. 10000 would signify 100.00
/// degrees Celcius.
/// 
/// *Note*: This won't handle edge cases very well.
pub fn lookup_temperature(val : u16) -> u32 {
    let mut first = &(0, 10000);
    let mut second = &(1000, 10390);
    let mut iterator = LOOKUP_TABLE.iter();
    while let Some(a) = iterator.next() {
        first = second;
        second = &a;
        if a.1 > val { break; }
    }
    let second = iterator.next();

    if let Some(second) = second {
        let temp = (second.0 - first.0) as u32 * (val - first.1) as u32 / (second.1 - first.1) as u32 + first.0 as u32;
        temp
    } else {
        0
    }
}