Use SI-prefixes that make sense for the given unit
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Juhani Krekelä
parent
3dee08d6d4
commit
d77a84fef1
219
src/format.rs
219
src/format.rs
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@ -1,66 +1,37 @@
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use crate::units::{Metric, MetricQuantity};
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pub fn format(quantity: MetricQuantity) -> String {
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let (amount, prefix) = si_prefix(quantity.amount);
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let unit = abbreviation(quantity.unit);
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let SiUnit(multiplier, unit) = si_unit(quantity);
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let amount = quantity.amount / multiplier;
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format!("{amount} {prefix}{unit}")
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format!("{amount} {unit}")
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}
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#[derive(Clone, Copy)]
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struct SiPrefix {
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prefix: &'static str,
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size: f64,
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}
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#[derive(Debug, PartialEq)]
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struct SiUnit(f64, &'static str);
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const SI_PREFIXES: [SiPrefix; 16] = [
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SiPrefix { prefix: "z", size: 0.000_000_000_000_000_000_001 },
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SiPrefix { prefix: "a", size: 0.000_000_000_000_000_001 },
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SiPrefix { prefix: "f", size: 0.000_000_000_000_001 },
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SiPrefix { prefix: "p", size: 0.000_000_000_001 },
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SiPrefix { prefix: "n", size: 0.000_000_001 },
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SiPrefix { prefix: "µ", size: 0.000_001 },
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SiPrefix { prefix: "m", size: 0.001 },
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SiPrefix { prefix: "c", size: 0.01 }, // Included for cm
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SiPrefix { prefix: "", size: 1.0 },
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SiPrefix { prefix: "k", size: 1_000.0 },
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SiPrefix { prefix: "M", size: 1_000_000.0 },
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SiPrefix { prefix: "G", size: 1_000_000_000.0 },
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SiPrefix { prefix: "T", size: 1_000_000_000_000.0 },
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SiPrefix { prefix: "P", size: 1_000_000_000_000_000.0 },
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SiPrefix { prefix: "E", size: 1_000_000_000_000_000_000.0 },
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SiPrefix { prefix: "Z", size: 1_000_000_000_000_000_000_000.0 },
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// Yotta and above cannot be represented exactly as a f64
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];
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fn si_unit(quantity: MetricQuantity) -> SiUnit {
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let absolute = quantity.amount.abs();
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fn si_prefix(amount: f64) -> (f64, &'static str) {
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let absolute = amount.abs();
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if absolute < SI_PREFIXES[0].size {
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let prefix = SI_PREFIXES[0];
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return (amount / prefix.size, prefix.prefix);
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}
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if absolute >= SI_PREFIXES[SI_PREFIXES.len() - 1].size {
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let prefix = SI_PREFIXES[SI_PREFIXES.len() - 1];
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return (amount / prefix.size, prefix.prefix);
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}
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// Find the correct prefix SI_PREFIX[index] such that:
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// SI_PREFIXES[index].size ≤ absolute < SI_PREFIXES[index + 1].size
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for index in 0..SI_PREFIXES.len() {
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if SI_PREFIXES[index].size <= absolute &&
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absolute < SI_PREFIXES[index + 1].size {
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let prefix = SI_PREFIXES[index];
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return (amount / prefix.size, prefix.prefix);
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match quantity.unit {
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Metric::Metre => {
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if absolute >= 1000.0 {
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return SiUnit(1000.0, "km");
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} else if absolute >= 1.0 {
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return SiUnit(1.0, "m");
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} else if absolute >= 0.01 {
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return SiUnit(0.01, "cm");
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} else {
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return SiUnit(0.001, "mm");
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}
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}
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Metric::Gram => {
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if absolute >= 1000.0 {
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return SiUnit(1000.0, "kg");
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} else {
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return SiUnit(1.0, "g");
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}
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}
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}
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unreachable!();
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}
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fn abbreviation(unit: Metric) -> &'static str {
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match unit {
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Metric::Metre => "m",
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Metric::Gram => "g",
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}
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}
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@ -70,47 +41,121 @@ mod test {
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#[test]
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fn quantities() {
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assert_eq!("1 m", &format(MetricQuantity {
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amount: 1.0,
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assert_eq!("0.1 mm", &format(MetricQuantity {
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amount: 0.000_1,
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unit: Metric::Metre,
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}));
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assert_eq!("5 kg", &format(MetricQuantity {
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amount: 5_000.0,
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assert_eq!("-1 m", &format(MetricQuantity {
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amount: -1.0,
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unit: Metric::Metre,
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}));
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assert_eq!("1.5 m", &format(MetricQuantity {
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amount: 1.5,
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unit: Metric::Metre,
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}));
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assert_eq!("1000 km", &format(MetricQuantity {
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amount: 1_000_000.0,
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unit: Metric::Metre,
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}));
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assert_eq!("-5 g", &format(MetricQuantity {
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amount: -5.0,
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unit: Metric::Gram,
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}));
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assert_eq!("25.5 cm", &format(MetricQuantity {
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amount: 0.255,
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unit: Metric::Metre,
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assert_eq!("3.2 kg", &format(MetricQuantity {
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amount: 3_200.0,
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unit: Metric::Gram,
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}));
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}
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#[test]
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fn prefixes() {
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assert_eq!(si_prefix(0.000_000_000_000_000_000_0005), (0.5, "z"));
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assert_eq!(si_prefix(0.000_000_000_000_000_000_001), (1.0, "z"));
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assert_eq!(si_prefix(0.000_000_000_000_000_000_01), (10.0, "z"));
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assert_eq!(si_prefix(0.000_000_000_000_000_00_01), (100.0, "z"));
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assert_eq!(si_prefix(0.000_000_000_000_000_001), (1.0, "a"));
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assert_eq!(si_prefix(0.000_000_000_000_001), (1.0, "f"));
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assert_eq!(si_prefix(0.000_000_000_001), (1.0, "p"));
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assert_eq!(si_prefix(0.000_000_001), (1.0, "n"));
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assert_eq!(si_prefix(0.000_001), (1.0, "µ"));
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assert_eq!(si_prefix(0.001), (1.0, "m"));
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assert_eq!(si_prefix(0.01), (1.0, "c"));
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assert_eq!(si_prefix(1.0), (1.0, ""));
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assert_eq!(si_prefix(1_000.0), (1.0, "k"));
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assert_eq!(si_prefix(1_000_000.0), (1.0, "M"));
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assert_eq!(si_prefix(1_000_000_000.0), (1.0, "G"));
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assert_eq!(si_prefix(1_000_000_000_000.0), (1.0, "T"));
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assert_eq!(si_prefix(1_000_000_000_000_000.0), (1.0, "P"));
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assert_eq!(si_prefix(1_000_000_000_000_000_000.0), (1.0, "E"));
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assert_eq!(si_prefix(10_000_000_000_000_000_000.0), (10.0, "E"));
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assert_eq!(si_prefix(100_000_000_000_000_000_000.0), (100.0, "E"));
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assert_eq!(si_prefix(1_000_000_000_000_000_000_000.0), (1.0, "Z"));
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assert_eq!(si_prefix(2_000_000_000_000_000_000_000.0), (2.0, "Z"));
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fn units() {
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assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
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amount: 0.0001,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
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amount: 0.001,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
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amount: 0.01,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
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amount: 0.1,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
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amount: 1.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
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amount: 10.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
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amount: 100.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
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amount: 1000.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
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amount: 10_000.0,
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unit: Metric::Metre,
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}));
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assert_eq!(si_prefix(-0.000_000_000_000_000_000_0005), (-0.5, "z"));
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assert_eq!(si_prefix(-0.5), (-50.0, "c"));
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assert_eq!(si_prefix(-2_000_000_000_000_000_000_000.0), (-2.0, "Z"));
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assert_eq!(SiUnit(0.001, "mm"), si_unit(MetricQuantity {
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amount: -0.001,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(0.01, "cm"), si_unit(MetricQuantity {
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amount: -0.01,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1.0, "m"), si_unit(MetricQuantity {
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amount: -1.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1000.0, "km"), si_unit(MetricQuantity {
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amount: -1000.0,
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unit: Metric::Metre,
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}));
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assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
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amount: 0.1,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
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amount: 1.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
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amount: 10.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
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amount: 100.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
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amount: 1000.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
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amount: 10_1000.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1.0, "g"), si_unit(MetricQuantity {
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amount: -1.0,
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unit: Metric::Gram,
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}));
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assert_eq!(SiUnit(1000.0, "kg"), si_unit(MetricQuantity {
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amount: -1000.0,
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unit: Metric::Gram,
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}));
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}
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}
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@ -17,7 +17,7 @@ pub enum NonMetric {
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Stone,
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}
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#[derive(Debug, PartialEq)]
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#[derive(Clone, Copy, Debug, PartialEq)]
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pub struct MetricQuantity {
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pub amount: f64,
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pub unit: Metric,
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