Lib.rs

Static fractions

Static fractions, as introduced in this crate, are numeric data types that represent a fraction, store their numerator in memory and their denominator in code. They are a generalization of fixed-point numbers.

For example (and not all of this is implemented yet):

// The range 0-255 means voltages from 0V (0/1) to 1.25V (125/100).
StaticFractionType!(VoltageFromADC, 0u8, 255u8, 0, 1, 125, 100);

fn adc_read() -> VoltageFromADC {
    let adc_readout: u8 = lowlevel_adc_read();
    VoltageFromADC::new_from_stored(adc_readout)
}

let current = static_fraction(10, 1000); // 10mA
let resistance_at_zero = 100; // 100ohm
let resistance_per_deg = static_fraction(4, 100); // 0.04ohm/degC

let resistance = adc_read() / current;
let temperature = 0 + (resistance - resistance_at_zero) / resistance_per_deg; // in degC

if temperature > 30 { fan_on(); }
if temperature < 20 { fan_off(); }

The idea is that

• raw data can be stored in as compact a data type as it arrives
• any datum can be used in calculations without needing to know more than its unit
• all operations can be performed in integer arithmetic (so they don't pull floating point emulation onto devices without floating point support)
• possibly, intermediate results can be stored in a compact way (where it's as of now completely unclear how the tradeof between precision and storage will be decided)