plotters/data/
float.rs

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

plotters/data/
float.rs
