fixed_wide_vectors/fixed_wide_traits/src/narrow.rs

pub trait Narrow{
	type Output;
	fn narrow(self)->Self::Output;
}
#[derive(Debug)]
pub enum Error{
	Overflow,
	Underflow,
}
impl std::fmt::Display for Error{
	fn fmt(&self,f:&mut std::fmt::Formatter<'_>)->std::fmt::Result{
		write!(f,"{self:?}")
	}
}
impl std::error::Error for Error{}
pub trait TryNarrow{
	type Output;
	fn try_narrow(self)->Result<Self::Output,Error>;
}
#[cfg(test)]
mod tests {
	use super::*;

	//TODO: use num_traits to do a blanket implementation (self<T::MIN as U)
	impl TryNarrow for i16{
		type Output=i8;
		fn try_narrow(self)->Result<Self::Output,Error>{
			if self<i8::MIN as i16{
				return Err(Error::Underflow);
			}
			if (i8::MAX as i16)<self{
				return Err(Error::Overflow);
			}
			Ok(self as i8)
		}
	}

	#[test]
	fn test_i16_i8(){
		assert!(matches!(257i16.try_narrow(),Err(Error::Overflow)));
		assert!(matches!(64i16.try_narrow(),Ok(64i8)));
		assert!(matches!((-257i16).try_narrow(),Err(Error::Underflow)));
	}

	impl Narrow for fixed::FixedI16<typenum::consts::U8>{
		type Output=i8;
		fn narrow(self)->Self::Output{
			(self.to_bits()>>8) as i8
		}
	}

	#[test]
	fn test_fixed_i16_i8(){
		let a=fixed::FixedI16::<typenum::consts::U8>::from(5)/2;
		assert_eq!(a.narrow(),2);
	}
}