macro_rules! implement {
($(#[$attribute:meta])* pub $name:ident($kind:ty | $fraction:literal)) => {
$(#[$attribute])*
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct $name(pub $kind);
impl From<$name> for f32 {
#[inline]
fn from(number: $name) -> Self {
const SCALE: f32 = (1 << $fraction) as f32;
(number.0 as f32) / SCALE
}
}
impl crate::value::Read for $name {
#[inline]
fn read<T: crate::tape::Read>(tape: &mut T) -> $crate::Result<Self> {
Ok($name(tape.take()?))
}
}
impl crate::value::Write for $name {
#[inline]
fn write<T: crate::tape::Write>(&self, tape: &mut T) -> $crate::Result<()> {
tape.give(&self.0)
}
}
}
}
implement! {
#[doc = "A fixed-point number in format Q2.14."]
#[allow(non_camel_case_types)]
pub q16(i16 | 14)
}
implement! {
#[doc = "A fixed-point number in format Q16.16."]
#[allow(non_camel_case_types)]
pub q32(i32 | 16)
}
#[cfg(test)]
mod tests {
use super::q16;
#[test]
fn from() {
use std::mem::transmute;
let cases: Vec<(i16, f32)> = vec![
(unsafe { transmute::<u16, i16>(0x7fff) }, 1.999939),
(unsafe { transmute::<u16, i16>(0x7000) }, 1.75),
(unsafe { transmute::<u16, i16>(0x0001) }, 0.000061),
(unsafe { transmute::<u16, i16>(0x0000) }, 0.0),
(unsafe { transmute::<u16, i16>(0xffff) }, -0.000061),
(unsafe { transmute::<u16, i16>(0x8000) }, -2.0),
];
for (input, output) in cases.into_iter() {
let input: f32 = q16(input).into();
assert!((input - output).abs() < 1e-4, "{} != {}", input, output);
}
}
}