askama/filters/
humansize.rs

1use core::convert::Infallible;
2use core::fmt;
3use core::mem::MaybeUninit;
4
5use super::FastWritable;
6use crate::ascii_str::{AsciiChar, AsciiStr};
7
8/// Returns adequate string representation (in KB, ..) of number of bytes
9///
10/// ## Example
11/// ```
12/// # use askama::Template;
13/// #[derive(Template)]
14/// #[template(
15///     source = "Filesize: {{ size_in_bytes|filesizeformat }}.",
16///     ext = "html"
17/// )]
18/// struct Example {
19///     size_in_bytes: u64,
20/// }
21///
22/// let tmpl = Example { size_in_bytes: 1_234_567 };
23/// assert_eq!(tmpl.to_string(),  "Filesize: 1.23 MB.");
24/// ```
25#[inline]
26pub fn filesizeformat(b: f32) -> Result<FilesizeFormatFilter, Infallible> {
27    Ok(FilesizeFormatFilter(b))
28}
29
30#[derive(Debug, Clone, Copy)]
31pub struct FilesizeFormatFilter(f32);
32
33impl fmt::Display for FilesizeFormatFilter {
34    #[inline]
35    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
36        Ok(self.write_into(f)?)
37    }
38}
39
40impl FastWritable for FilesizeFormatFilter {
41    fn write_into<W: fmt::Write + ?Sized>(&self, dest: &mut W) -> crate::Result<()> {
42        if self.0 < 1e3 {
43            (self.0 as u32).write_into(dest)?;
44            Ok(dest.write_str(" B")?)
45        } else if let Some((prefix, factor)) = SI_PREFIXES
46            .iter()
47            .copied()
48            .find_map(|(prefix_factor, max)| (self.0 < max).then_some(prefix_factor))
49        {
50            // u32 is big enough to hold the number 999_999
51            let scaled = (self.0 * factor) as u32;
52            (scaled / 100).write_into(dest)?;
53            format_frac(&mut MaybeUninit::uninit(), prefix, scaled).write_into(dest)
54        } else {
55            too_big(self.0, dest)
56        }
57    }
58}
59
60/// Formats `buffer` to contain the decimal point, decimal places and unit
61fn format_frac(buffer: &mut MaybeUninit<[AsciiChar; 8]>, prefix: AsciiChar, scaled: u32) -> &str {
62    // LLVM generates better byte code for register sized buffers
63    let buffer = buffer.write(AsciiStr::new_sized("..0 kB"));
64    buffer[4] = prefix;
65
66    let frac = scaled % 100;
67    let buffer = if frac == 0 {
68        &buffer[3..6]
69    } else {
70        let digits = AsciiChar::two_digits(frac);
71        if digits[1] == AsciiChar::new(b'0') {
72            // the decimal separator '.' is already contained in buffer[1]
73            buffer[2] = digits[0];
74            &buffer[1..6]
75        } else {
76            // the decimal separator '.' is already contained in buffer[0]
77            [buffer[1], buffer[2]] = digits;
78            &buffer[0..6]
79        }
80    };
81    AsciiStr::from_slice(buffer).as_str()
82}
83
84#[cold]
85fn too_big<W: fmt::Write + ?Sized>(value: f32, dest: &mut W) -> crate::Result<()> {
86    // the value exceeds 999 QB, so we omit the decimal places
87    Ok(write!(dest, "{:.0} QB", value / 1e30)?)
88}
89
90/// `((si_prefix, factor), limit)`, the factor is offset by 10**2 to account for 2 decimal places
91const SI_PREFIXES: &[((AsciiChar, f32), f32)] = &[
92    ((AsciiChar::new(b'k'), 1e-1), 1e6),
93    ((AsciiChar::new(b'M'), 1e-4), 1e9),
94    ((AsciiChar::new(b'G'), 1e-7), 1e12),
95    ((AsciiChar::new(b'T'), 1e-10), 1e15),
96    ((AsciiChar::new(b'P'), 1e-13), 1e18),
97    ((AsciiChar::new(b'E'), 1e-16), 1e21),
98    ((AsciiChar::new(b'Z'), 1e-19), 1e24),
99    ((AsciiChar::new(b'Y'), 1e-22), 1e27),
100    ((AsciiChar::new(b'R'), 1e-25), 1e30),
101    ((AsciiChar::new(b'Q'), 1e-28), 1e33),
102];
103
104#[test]
105#[cfg(feature = "alloc")]
106fn test_filesizeformat() {
107    use alloc::string::ToString;
108
109    assert_eq!(filesizeformat(0.).unwrap().to_string(), "0 B");
110    assert_eq!(filesizeformat(999.).unwrap().to_string(), "999 B");
111    assert_eq!(filesizeformat(1000.).unwrap().to_string(), "1 kB");
112    assert_eq!(filesizeformat(1023.).unwrap().to_string(), "1.02 kB");
113    assert_eq!(filesizeformat(1024.).unwrap().to_string(), "1.02 kB");
114    assert_eq!(filesizeformat(1100.).unwrap().to_string(), "1.1 kB");
115    assert_eq!(filesizeformat(9_499_014.).unwrap().to_string(), "9.49 MB");
116    assert_eq!(
117        filesizeformat(954_548_589.2).unwrap().to_string(),
118        "954.54 MB"
119    );
120}
askama/filters/humansize.rs

askama/filters/
humansize.rs
