plotters/data/
float.rs

1// The code that is related to float number handling
2fn find_minimal_repr(n: f64, eps: f64) -> (f64, usize) {
3    if eps >= 1.0 {
4        return (n, 0);
5    }
6    if n - n.floor() < eps {
7        (n.floor(), 0)
8    } else if n.ceil() - n < eps {
9        (n.ceil(), 0)
10    } else {
11        let (rem, pre) = find_minimal_repr((n - n.floor()) * 10.0, eps * 10.0);
12        (n.floor() + rem / 10.0, pre + 1)
13    }
14}
15
16#[allow(clippy::never_loop)]
17fn float_to_string(n: f64, max_precision: usize, min_decimal: usize) -> String {
18    let (mut result, mut count) = loop {
19        let (sign, n) = if n < 0.0 { ("-", -n) } else { ("", n) };
20        let int_part = n.floor();
21
22        let dec_part =
23            ((n.abs() - int_part.abs()) * (10.0f64).powi(max_precision as i32)).round() as u64;
24
25        if dec_part == 0 || max_precision == 0 {
26            break (format!("{}{:.0}", sign, int_part), 0);
27        }
28
29        let mut leading = "".to_string();
30        let mut dec_result = format!("{}", dec_part);
31
32        for _ in 0..(max_precision - dec_result.len()) {
33            leading.push('0');
34        }
35
36        while let Some(c) = dec_result.pop() {
37            if c != '0' {
38                dec_result.push(c);
39                break;
40            }
41        }
42
43        break (
44            format!("{}{:.0}.{}{}", sign, int_part, leading, dec_result),
45            leading.len() + dec_result.len(),
46        );
47    };
48
49    if count == 0 && min_decimal > 0 {
50        result.push('.');
51    }
52
53    while count < min_decimal {
54        result.push('0');
55        count += 1;
56    }
57    result
58}
59
60/// Handles printing of floating point numbers
61pub struct FloatPrettyPrinter {
62    /// Whether scientific notation is allowed
63    pub allow_scientific: bool,
64    /// Minimum allowed number of decimal digits
65    pub min_decimal: i32,
66    /// Maximum allowed number of decimal digits
67    pub max_decimal: i32,
68}
69
70impl FloatPrettyPrinter {
71    /// Handles printing of floating point numbers
72    pub fn print(&self, n: f64) -> String {
73        let (tn, p) = find_minimal_repr(n, (10f64).powi(-self.max_decimal));
74        let d_repr = float_to_string(tn, p, self.min_decimal as usize);
75        if !self.allow_scientific {
76            d_repr
77        } else {
78            if n == 0.0 {
79                return "0".to_string();
80            }
81
82            let mut idx = n.abs().log10().floor();
83            let mut exp = (10.0f64).powf(idx);
84
85            if n.abs() / exp + 1e-5 >= 10.0 {
86                idx += 1.0;
87                exp *= 10.0;
88            }
89
90            if idx.abs() < 3.0 {
91                return d_repr;
92            }
93
94            let (sn, sp) = find_minimal_repr(n / exp, 1e-5);
95            let s_repr = format!(
96                "{}e{}",
97                float_to_string(sn, sp, self.min_decimal as usize),
98                float_to_string(idx, 0, 0)
99            );
100            if s_repr.len() + 1 < d_repr.len() || (tn == 0.0 && n != 0.0) {
101                s_repr
102            } else {
103                d_repr
104            }
105        }
106    }
107}
108
109/// The function that pretty prints the floating number
110/// Since rust doesn't have anything that can format a float with out appearance, so we just
111/// implement a float pretty printing function, which finds the shortest representation of a
112/// floating point number within the allowed error range.
113///
114/// - `n`: The float number to pretty-print
115/// - `allow_sn`: Should we use scientific notation when possible
116/// - **returns**: The pretty printed string
117pub fn pretty_print_float(n: f64, allow_sn: bool) -> String {
118    (FloatPrettyPrinter {
119        allow_scientific: allow_sn,
120        min_decimal: 0,
121        max_decimal: 10,
122    })
123    .print(n)
124}
125
126#[cfg(test)]
127mod test {
128    use super::*;
129    #[test]
130    fn test_pretty_printing() {
131        assert_eq!(pretty_print_float(0.99999999999999999999, false), "1");
132        assert_eq!(pretty_print_float(0.9999, false), "0.9999");
133        assert_eq!(
134            pretty_print_float(-1e-5 - 0.00000000000000001, true),
135            "-1e-5"
136        );
137        assert_eq!(
138            pretty_print_float(-1e-5 - 0.00000000000000001, false),
139            "-0.00001"
140        );
141        assert_eq!(pretty_print_float(1e100, true), "1e100");
142        assert_eq!(pretty_print_float(1234567890f64, true), "1234567890");
143        assert_eq!(pretty_print_float(1000000001f64, true), "1e9");
144    }
145}
plotters/data/float.rs

plotters/data/
float.rs
