yuurei/src/ext.rs

//! Extensions
use super::*;

pub trait VecExt<T>
{
    /// Insert many elements
    fn move_insert<Ex, I: IntoIterator<Item = T, IntoIter = Ex>>(&mut self, location: usize, slice: I)
    where Ex: ExactSizeIterator<Item = T> + std::panic::UnwindSafe;

    /// Insert many elements
    fn splice_insert<I: IntoIterator<Item =T>>(&mut self, location: usize, slice: I);
}


impl<T> VecExt<T> for Vec<T>
{
    fn move_insert<Ex, I: IntoIterator<Item = T, IntoIter = Ex>>(&mut self, location: usize, slice: I)
    where Ex: ExactSizeIterator<Item = T> + std::panic::UnwindSafe,
    {
	#[inline(never)]
	#[cold]
	fn panic_len(l1: usize, l2: usize) -> !
	{
	    panic!("Location must be in range 0..{}, got {}", l1,l2)
	}

	#[inline(never)]
	#[cold]
	fn inv_sz() -> !
	{
	    panic!("ExactSizeIterator returned invalid size");
	}

	if location >= self.len() {
	    panic_len(self.len(), location);
	}
	let mut slice = slice.into_iter();

	let slen = slice.len();
	match slen {
	    0 => return,
	    1 => {
		self.insert(location, slice.next().unwrap());
		return
	    },
	    _ => (),
	};
	self.reserve(slice.len());

	unsafe {
	    let this = self.as_mut_ptr().add(location);
	    let len = self.len();
	    let rest = std::mem::size_of::<T>() * (location..len).len();
	    
	    libc::memmove(this.add(slen) as *mut libc::c_void, this as *mut libc::c_void, rest);
	    let mut sent=0;
	    match std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
		let mut this = this;
		for item in slice {
		    if sent >= slen {
			inv_sz();
		    }
		    
		    this.write(item);
		    this = this.add(1);
		    sent+=1;
		}
		if sent != slen {
		    inv_sz();
		}
	    })) {
		Err(e) => {
		    // memory at (location+sent)..slen is now invalid, move the old one back before allowing unwind to contine
		    libc::memmove(this.add(sent) as *mut libc::c_void, this.add(slen) as *mut libc::c_void, rest);
		    std::panic::resume_unwind(e)
		},
		_ => (),
	    }
	    self.set_len(len + sent);
	}
    }
    fn splice_insert<I: IntoIterator<Item =T>>(&mut self, location: usize, slice: I)
    {
	let slice = slice.into_iter();
	match slice.size_hint() {
	    (0, Some(0)) | (0, None) => (),
	    (_, Some(bound)) | (bound, _) => self.reserve(bound),
	};
	// shift everything across, replacing with the new values
	let splice: Vec<_> = self.splice(location.., slice).collect();
	// add tail back
	self.extend(splice);
    }
}

#[cfg(test)]
mod tests
{
    use super::*;
    #[test]
    fn vec_move_insert()
    {
	let mut vec = vec![0,1,2,8,9,10];
	vec.move_insert(3, [3,4,5,6, 7].iter().copied());

	assert_eq!(&vec[..],
		   &[0,1,2,3,4,5,6,7,8,9,10]
	);
    }
    #[test]
    fn vec_move_insert_nt()
    {
	macro_rules! string {
	    ($str:literal) => (String::from($str));
	}
	let mut vec = vec![
	    string!("Hello"),
	    string!("world"),
	    string!("foo"),
	    string!("uhh"),
	];
	let vec2 = vec![
	    string!("Hello"),
	    string!("world"),
	    string!("hi"),
	    string!("hello"),
	    string!("foo"),
	    string!("uhh"),
	];

	vec.move_insert(2, vec![string!("hi"), string!("hello")]);

	assert_eq!(&vec[..], &vec2[..]);
    }
    
    #[cfg(nightly)]
    mod benchmatks
    {
	use super::super::*;
	use test::{
	    Bencher, black_box,
	};
	#[bench]
	fn move_via_splice(b: &mut Bencher)
	{
	    let mut vec = vec![0,10,11,12];
	    let span = [0,1,2,3];

	    b.iter(|| {
		black_box(vec.splice_insert(2, span.iter().copied()));
	    });
	}
	#[bench]
	fn move_via_unsafe(b: &mut Bencher)
	{
	    let mut vec = vec![0,10,11,12];
	    let span = [0,1,2,3];
	    b.iter(|| {
		black_box(vec.move_insert(2, span.iter().copied()));
	    });
	}
    }

}