113 lines
3.7 KiB
Rust
113 lines
3.7 KiB
Rust
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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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format!("{amount} {prefix}{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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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_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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}
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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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#[cfg(test)]
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mod test {
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use super::*;
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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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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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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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}));
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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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}
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}
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