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use std::{sync::Arc};
const INLINE_CAP: usize = 22;
const WS_TAG: u8 = (INLINE_CAP + 1) as u8;
#[derive(Clone, Debug)]
pub(crate) enum SmolStr {
Heap(Arc<str>),
Inline {
len: u8,
buf: [u8; INLINE_CAP],
},
}
impl SmolStr {
pub fn new(text: &str) -> SmolStr {
let len = text.len();
if len <= INLINE_CAP {
let mut buf = [0; INLINE_CAP];
buf[..len].copy_from_slice(text.as_bytes());
return SmolStr::Inline { len: len as u8, buf };
}
let newlines = text.bytes().take_while(|&b| b == b'\n').count();
let spaces = text[newlines..].bytes().take_while(|&b| b == b' ').count();
if newlines + spaces == len && newlines <= N_NEWLINES && spaces <= N_SPACES {
let mut buf = [0; INLINE_CAP];
buf[0] = newlines as u8;
buf[1] = spaces as u8;
return SmolStr::Inline { len: WS_TAG, buf };
}
SmolStr::Heap(
text.to_string().into_boxed_str().into()
)
}
pub fn as_str(&self) -> &str {
match self {
SmolStr::Heap(data) => &*data,
SmolStr::Inline { len, buf } => {
if *len == WS_TAG {
let newlines = buf[0] as usize;
let spaces = buf[1] as usize;
assert!(newlines <= N_NEWLINES && spaces <= N_SPACES);
return &WS[N_NEWLINES - newlines..N_NEWLINES + spaces]
}
let len = *len as usize;
let buf = &buf[..len];
unsafe { ::std::str::from_utf8_unchecked(buf) }
}
}
}
}
const N_NEWLINES: usize = 32;
const N_SPACES: usize = 128;
const WS: &str =
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n ";
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[cfg(target_pointer_width = "64")]
fn smol_str_is_smol() {
assert_eq!(::std::mem::size_of::<SmolStr>(), 8 + 8 + 8)
}
#[test]
fn test_round_trip() {
let mut text = String::new();
for n in 0..256 {
let smol = SmolStr::new(&text);
assert_eq!(smol.as_str(), text.as_str());
text.push_str(&n.to_string());
}
}
}
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